Drugs for infections

Drugs for infections

Drugs used for infections include antibacterials, antifungals, antivirals, antimycobacterials and antiparasitic drugs.

Antibacterials which act to kill or inhibit the growth of bacteria, target essential bacterial molecular pathways not shared with the host (e.g. inhibiting nucleic acid precursor synthesis, protein synthesis, and cell membrane integrity). Antifungal drugs utilize similar mechanisms, targeting fungal cell wall-synthesizing enzymes for example. The machinery of viral replication are targets for antiviral drugs including HIV, and drugs used in treating mycobacterial infections represent another spectrum of action of drugs for infections.

 

Parts of this module are under construction. If you have relevant content you are willing to share, we would appreciate your contribution. Contact admin@pharmacologyeducation.org, or complete the webform on the Contribute to the Project page.

Anti-malarial drugs

The learning resources at the bottom of this page provide links to reliable online materials that present current information about both the Plasmodium species responsible for malaria in humans, and the parasite's lifecycle. These are useful as refreshers for learners.

Non-drug based interventions are effective and include bite-prevention strategies such as protective clothing, mosquito nets, vaporised insecticides and insect repellents that are applied to the skin.

Pharmaceutical treatment and prophylaxis of malaria relies on drugs that target the parasite at crucial stages of its lifecycle. Current drugs kill the asexual blood stage (a.k.a. erythrocytic forms, or schizonts) of the parasite in the blood, the primary and latent liver stages, or gametocytes.

The artemisinins (artesunate, artemether, lumefantrine), chloroquine, mefloquine, quinolones (quinine, quinidine), and antibacterial anti-malarials (pyrimethamine, sulfadoxine, doxycycline, clindamycin) all kill plasmodium parasites during the asexual blood stage.

Atovaquone + proguanil provides additional activity against the primary liver stages of P. falciparum.

Primaquine is effective against primary and latent liver stages as well as gametocytes, and it is most commonly used to eradicate the intrahepatic hypnozoites of P. vivax and P. ovale that are responsible for relapsing infections.

Prophylaxis and Treatment of Malaria
Selecting appropriate drug or drug combination for prophylaxis or treatment is based on the susceptibility of the infecting parasite as determined by the geographical area where the infection was acquired. This map from the US Centers for Disease Control and Prevention (CDC) shows an approximation of the parts of the world where malaria transmission occurs. A map showing an approximation of the parts of the world where malaria transmission occurs

 

Drug based prophylaxis (chemoprophylaxis):

Short-term prophylaxis is recommended for residents from non-malarious countries who are travelling into areas where malaria is endemic. Best practice is to commence treatment before travel into a malaria zone, and to continue for a prescribed period of time after leaving the area.

The drugs used include chloroquine, mefloquine, atovaquone+proguanil and doxycycline. These drugs can be used for long-term prophylaxis and the choice of drug depends upon the extent of anti-malarial drug resistance in the destination area. 

Treating Falciparum malaria (caused by Plasmodium falciparum):

All patients with Falciparum malaria should be admitted for hospital treatment, as there is a high risk of rapid deterioration, even once treatment has been initiated.

First-line treatment for uncomplicated Falciparum malaria is combination artemisinin drugs:  Artemether with lumefantrine is the primary option, with artenimol with piperaquine phosphate as an alternative.  Oral quinine or atovaquone + proguanil hydrochloride is suitable if an artemisinin combination is not available. Quinine is highly effective but poorly tolerated if treatment is prolonged, and this is usually prescribed in combination with oral doxycycline.

If the infection becomes severe or complicated, high dependency or intensive care is necessary, patients should be treated using Intravenous artesunate. If artesunate is temporarily unavailable, i.v. quinine can be administered until the artesunate  arrives. If the patient responds to the initial artesunate, they should be switched to a full course of artemisinin combination therapy (oral quinine + doxycycline, or atovaquone + proguanil hydrochloride are suitable alternatives as described above).

Most P. falciparum is resistant to chloroquine, voiding its use. Due to concerns about adverse effects of mefloquine, the drug is used only when no other treatment options are available.

Treating non-falciparum malaria (caused by Plasmodium vivax, P. ovale, P. malariae,  or P. knowlesi, dependent on geographic location):

The first-line options for P. vivax infections are artemisinin combination therapies, or chloroquine. Artemisinin combinations might offer better coverage in some regions due to chloroquine-resistant strains of P. vivax.

Because of its high activity against hypnozoites, primaquine is used for terminal chemoprophylaxis and radical cure of P. vivax and P. ovale infection.

 

 

This webpage provides information about the species of Plasmodium that are recognised as causing malaria in humans around the globe. It is regularly updated.

Average: 1 (1 vote)

The learning resources at the bottom of this page provide links to reliable online materials that present current information about both the Plasmodium species responsible for malaria in humans, and the parasite's lifecycle. These are useful as refreshers for learners.

Non-drug based interventions are effective and include bite-prevention strategies such as protective clothing, mosquito nets, vaporised insecticides and insect repellents that are applied to the skin.

Pharmaceutical treatment and prophylaxis of malaria relies on drugs that target the parasite at crucial stages of its lifecycle. Current drugs kill the asexual blood stage (a.k.a. erythrocytic forms, or schizonts) of the parasite in the blood, the primary and latent liver stages, or gametocytes.

The artemisinins (artesunate, artemether, lumefantrine), chloroquine, mefloquine, quinolones (quinine, quinidine), and antibacterial anti-malarials (pyrimethamine, sulfadoxine, doxycycline, clindamycin) all kill plasmodium parasites during the asexual blood stage.

Atovaquone + proguanil provides additional activity against the primary liver stages of P. falciparum.

Primaquine is effective against primary and latent liver stages as well as gametocytes, and it is most commonly used to eradicate the intrahepatic hypnozoites of P. vivax and P. ovale that are responsible for relapsing infections.

Prophylaxis and Treatment of Malaria
Selecting appropriate drug or drug combination for prophylaxis or treatment is based on the susceptibility of the infecting parasite as determined by the geographical area where the infection was acquired. This map from the US Centers for Disease Control and Prevention (CDC) shows an approximation of the parts of the world where malaria transmission occurs. A map showing an approximation of the parts of the world where malaria transmission occurs

 

Drug based prophylaxis (chemoprophylaxis):

Short-term prophylaxis is recommended for residents from non-malarious countries who are travelling into areas where malaria is endemic. Best practice is to commence treatment before travel into a malaria zone, and to continue for a prescribed period of time after leaving the area.

The drugs used include chloroquine, mefloquine, atovaquone+proguanil and doxycycline. These drugs can be used for long-term prophylaxis and the choice of drug depends upon the extent of anti-malarial drug resistance in the destination area. 

Treating Falciparum malaria (caused by Plasmodium falciparum):

All patients with Falciparum malaria should be admitted for hospital treatment, as there is a high risk of rapid deterioration, even once treatment has been initiated.

First-line treatment for uncomplicated Falciparum malaria is combination artemisinin drugs:  Artemether with lumefantrine is the primary option, with artenimol with piperaquine phosphate as an alternative.  Oral quinine or atovaquone + proguanil hydrochloride is suitable if an artemisinin combination is not available. Quinine is highly effective but poorly tolerated if treatment is prolonged, and this is usually prescribed in combination with oral doxycycline.

If the infection becomes severe or complicated, high dependency or intensive care is necessary, patients should be treated using Intravenous artesunate. If artesunate is temporarily unavailable, i.v. quinine can be administered until the artesunate  arrives. If the patient responds to the initial artesunate, they should be switched to a full course of artemisinin combination therapy (oral quinine + doxycycline, or atovaquone + proguanil hydrochloride are suitable alternatives as described above).

Most P. falciparum is resistant to chloroquine, voiding its use. Due to concerns about adverse effects of mefloquine, the drug is used only when no other treatment options are available.

Treating non-falciparum malaria (caused by Plasmodium vivax, P. ovale, P. malariae,  or P. knowlesi, dependent on geographic location):

The first-line options for P. vivax infections are artemisinin combination therapies, or chloroquine. Artemisinin combinations might offer better coverage in some regions due to chloroquine-resistant strains of P. vivax.

Because of its high activity against hypnozoites, primaquine is used for terminal chemoprophylaxis and radical cure of P. vivax and P. ovale infection.

 

 

This wepage provides links to an animated PowerPoint slide and short animated movies that describe the lifecycle of the Plasmodium parasite. It was developed in collaboration with the Medicines for Malaria Venture (MMV).

No votes yet

Drugs for SARS-CoV-2 infection (COVID-19)

COVID-19 is the disease caused by infection by SARS-CoV-2 (severe acute respiratory syndrome virus 2), the airbourne, respiratory coronavirus that was first detected in China’s city of Wuhan in late 2019. The spread of this virus rapidly became a global pandemic that has resulted in millions of deaths. The pace of the subsequent response by the medical, pharmacology, scientific and pharmaceutical research communities has been unprecedented and delvered significant advances in both vaccinations and therapeutic interventions.

Whilst vaccinations that stimulate an immune response against SARS-CoV-2 have proved effective in preventing severe respiratory complications, this section will focus on the drugs that alter disease pathology or inhibit virus infection. A huge effort has been made to understand the host factors that may affect the severity of disease experienced by individual patients, and therefore provide pharmaclogical targets with potential to modify the disease progression. Thousands of clinical trials have evaluated both existing drugs, repurposed for SARS-CoV-2 infection, or drugs that were in development for other diseases.

Initially, medical interventions for hospitalised COVID-19 patients was supportive and aimed to improve oxygenation in the face of infection-induced lung damage. In patients that progressed to acute respiratory distress syndrome (ARDS) this could extend to CPAP, intubation or extracorporeal membrane oxygenation (ECMO; although this is very limited in availability). It soon became apparent that severe COVID-19 might be accompanied by hyper-inflammation and microvascular clotting abnormalities that extended beyond the respiratory system, and that patients could experience rapid deterioration of pulmonary, cardiac, and/or neurological function. This emerging understanding of severe COVID-19 pathology led to the urgent search more targeted treatment options.

The University of Oxford-led “Randomised Evaluation of COVID-19 Therapy” (RECOVERY) trial has been instrumental in identifying therapeutic options for COVID-19 patients. RECOVERY is an international study, and as of April 2022 had provided evidence for 4 drugs that are effective COVID-19 treatments*. This page from the RECOVERY website shows the timeline of discoveries, and also (importantly) indicates some of the drugs that have shown no clinical benefit.

 

Therapies that are host-directed

Dexamethasone* is a widely available and relatively cheap corticosteroid (glucocorticoid receptor agonist) that targets the over-active immune response in patients with severe COVID-19. It has become the primary addition to standard care for critically ill COVID-19 patients.

Tocilizumab* is an anti-IL-6 receptor mAb, with immunosuppressive action that is approved for chronic autoimmune indications. Following many clinical studies, tocilizumab was found to decrease COVID-19 mortality, and in the UK can be used to treat critically ill COVID-19 patients in ICUs. In this setting, it is used in addition to corticosteroid therapy.

Baricitinib* is an oral Janus kinase inhibitor that has powerful anti-inflammatory activity. It is already used to treat severe rheumatoid arthritis, so its safety profile is well established. Baricitinib is indicated for hospitalised COVID-19 patients in addition to standard of care therapies such as immunomodulatory treatments (e.g. dexamethasone, tocilizumab) or the antiviral drug remdesivir.

To date the drugs that have demonstrated clinical benefit that holds up under RCT evaluation are those that modulate the inflammatory component of SARS-CoV-2 infection.

 

Therapies that target the virus

Anti-spike monoclonal antibodies

Several such mAbs were rapidly generated, either via analysis of plasma from recovered COVID-19 patients, and/or other mAb generation/optimisation strategies. A number of these have been authorised in different jurisdictions as COVID-19 therapies. Some are used in combinations, and work is ongoing to determine how effective they are in view of evolving SARS-CoV-2 variants.  Monoclonal antibodies are particularly useful for patients who either cannot be vaccinated or who don’t develop a strong vaccine response.

Regdanvimab is EMA authorised to treat SARS-CoV-2 positive patients with mild-moderate symptoms, who don’t require supplemental oxygen therapy, but who are at increased risk of progressing to severe disease.

Sotrovimab retains activity against the omicron (B.1.1.529) SARS-CoV-2 variant

Casirivimab + imdevimab (Ronapreve*) is a cocktail of two mAbs that have non-overlapping epitopes on the SARS-CoV-2 spike protein. Like regdanvimab, approval indicates Ronapreve use in confirmed COVID-19 patents with mild-moderate disease who are at high risk of progressing to severe disease.

A list of some other anti-spike mAbs is available on the Guide to PHARMACOLOGY

Mpro (main protease; 3CLpro)  inhibitors

Nirmatrelvir is the Mpro inhibitor component of Pfizer’s Paxlovid. Inhibiting Mpro blocks replication at an early stage in the virus' life cycle, so Paxlovid should be administered within 5 days of symptom onset. There is provisional evidence that nirmatrelvir retains activity against SARS-CoV-2 variants including delta and omicron. Paxlovid contains low dose ritonavir to inhibit CYP450-mediated metabolic clearance of nirmatrelvir.

RdRp (RNA-dependent RNA polymerase)  inhibitors

The conservation of RdRP catalytic domain between different RNA virus families means that inhibitors that were designed against other viral pathogens have some activity against the SARS coronaviruses.

One such inhibitor is remdesivir, which is a broad spectrum antiviral that was originally evaluated for anti-Ebola and anti-Marburg virus activity. In vitro activity against SARS and MERS coronaviruses had been demonstrated, so remdesivir was quickly tested for anti-SARS-CoV-2 activity. Anti-SARS-CoV-2 activity in in vitro systems and in animal models is low, and its clinical efficacy is not robust. However remdesivir was the first direct-acting antiviral to be FDA approved for COVID-19 (October 2020), in the rush to address the need for drug treatments for SARS-CoV-2 infections.  

This webpage provides information about drugs that are used to treat patients with COVID-19, as well as addressing both novel clinical candidates and alternative host and viral targets that under investigation. You can also use the search box (top right) to retrieve the full set of ligands and targets that have curated SARS-CoV-2 or COVID-19 related information, using the search terms SARS-CoV-2 or COVID-19.   

No votes yet

COVID-19 is the disease caused by infection by SARS-CoV-2 (severe acute respiratory syndrome virus 2), the airbourne, respiratory coronavirus that was first detected in China’s city of Wuhan in late 2019. The spread of this virus rapidly became a global pandemic that has resulted in millions of deaths. The pace of the subsequent response by the medical, pharmacology, scientific and pharmaceutical research communities has been unprecedented and delvered significant advances in both vaccinations and therapeutic interventions.

Whilst vaccinations that stimulate an immune response against SARS-CoV-2 have proved effective in preventing severe respiratory complications, this section will focus on the drugs that alter disease pathology or inhibit virus infection. A huge effort has been made to understand the host factors that may affect the severity of disease experienced by individual patients, and therefore provide pharmaclogical targets with potential to modify the disease progression. Thousands of clinical trials have evaluated both existing drugs, repurposed for SARS-CoV-2 infection, or drugs that were in development for other diseases.

Initially, medical interventions for hospitalised COVID-19 patients was supportive and aimed to improve oxygenation in the face of infection-induced lung damage. In patients that progressed to acute respiratory distress syndrome (ARDS) this could extend to CPAP, intubation or extracorporeal membrane oxygenation (ECMO; although this is very limited in availability). It soon became apparent that severe COVID-19 might be accompanied by hyper-inflammation and microvascular clotting abnormalities that extended beyond the respiratory system, and that patients could experience rapid deterioration of pulmonary, cardiac, and/or neurological function. This emerging understanding of severe COVID-19 pathology led to the urgent search more targeted treatment options.

The University of Oxford-led “Randomised Evaluation of COVID-19 Therapy” (RECOVERY) trial has been instrumental in identifying therapeutic options for COVID-19 patients. RECOVERY is an international study, and as of April 2022 had provided evidence for 4 drugs that are effective COVID-19 treatments*. This page from the RECOVERY website shows the timeline of discoveries, and also (importantly) indicates some of the drugs that have shown no clinical benefit.

 

Therapies that are host-directed

Dexamethasone* is a widely available and relatively cheap corticosteroid (glucocorticoid receptor agonist) that targets the over-active immune response in patients with severe COVID-19. It has become the primary addition to standard care for critically ill COVID-19 patients.

Tocilizumab* is an anti-IL-6 receptor mAb, with immunosuppressive action that is approved for chronic autoimmune indications. Following many clinical studies, tocilizumab was found to decrease COVID-19 mortality, and in the UK can be used to treat critically ill COVID-19 patients in ICUs. In this setting, it is used in addition to corticosteroid therapy.

Baricitinib* is an oral Janus kinase inhibitor that has powerful anti-inflammatory activity. It is already used to treat severe rheumatoid arthritis, so its safety profile is well established. Baricitinib is indicated for hospitalised COVID-19 patients in addition to standard of care therapies such as immunomodulatory treatments (e.g. dexamethasone, tocilizumab) or the antiviral drug remdesivir.

To date the drugs that have demonstrated clinical benefit that holds up under RCT evaluation are those that modulate the inflammatory component of SARS-CoV-2 infection.

 

Therapies that target the virus

Anti-spike monoclonal antibodies

Several such mAbs were rapidly generated, either via analysis of plasma from recovered COVID-19 patients, and/or other mAb generation/optimisation strategies. A number of these have been authorised in different jurisdictions as COVID-19 therapies. Some are used in combinations, and work is ongoing to determine how effective they are in view of evolving SARS-CoV-2 variants.  Monoclonal antibodies are particularly useful for patients who either cannot be vaccinated or who don’t develop a strong vaccine response.

Regdanvimab is EMA authorised to treat SARS-CoV-2 positive patients with mild-moderate symptoms, who don’t require supplemental oxygen therapy, but who are at increased risk of progressing to severe disease.

Sotrovimab retains activity against the omicron (B.1.1.529) SARS-CoV-2 variant

Casirivimab + imdevimab (Ronapreve*) is a cocktail of two mAbs that have non-overlapping epitopes on the SARS-CoV-2 spike protein. Like regdanvimab, approval indicates Ronapreve use in confirmed COVID-19 patents with mild-moderate disease who are at high risk of progressing to severe disease.

A list of some other anti-spike mAbs is available on the Guide to PHARMACOLOGY

Mpro (main protease; 3CLpro)  inhibitors

Nirmatrelvir is the Mpro inhibitor component of Pfizer’s Paxlovid. Inhibiting Mpro blocks replication at an early stage in the virus' life cycle, so Paxlovid should be administered within 5 days of symptom onset. There is provisional evidence that nirmatrelvir retains activity against SARS-CoV-2 variants including delta and omicron. Paxlovid contains low dose ritonavir to inhibit CYP450-mediated metabolic clearance of nirmatrelvir.

RdRp (RNA-dependent RNA polymerase)  inhibitors

The conservation of RdRP catalytic domain between different RNA virus families means that inhibitors that were designed against other viral pathogens have some activity against the SARS coronaviruses.

One such inhibitor is remdesivir, which is a broad spectrum antiviral that was originally evaluated for anti-Ebola and anti-Marburg virus activity. In vitro activity against SARS and MERS coronaviruses had been demonstrated, so remdesivir was quickly tested for anti-SARS-CoV-2 activity. Anti-SARS-CoV-2 activity in in vitro systems and in animal models is low, and its clinical efficacy is not robust. However remdesivir was the first direct-acting antiviral to be FDA approved for COVID-19 (October 2020), in the rush to address the need for drug treatments for SARS-CoV-2 infections.  

This article summarises the predicted efficacy of the clinically available anti-spike mAbs against the BA.2 omicrom subvariant.

No votes yet

COVID-19 is the disease caused by infection by SARS-CoV-2 (severe acute respiratory syndrome virus 2), the airbourne, respiratory coronavirus that was first detected in China’s city of Wuhan in late 2019. The spread of this virus rapidly became a global pandemic that has resulted in millions of deaths. The pace of the subsequent response by the medical, pharmacology, scientific and pharmaceutical research communities has been unprecedented and delvered significant advances in both vaccinations and therapeutic interventions.

Whilst vaccinations that stimulate an immune response against SARS-CoV-2 have proved effective in preventing severe respiratory complications, this section will focus on the drugs that alter disease pathology or inhibit virus infection. A huge effort has been made to understand the host factors that may affect the severity of disease experienced by individual patients, and therefore provide pharmaclogical targets with potential to modify the disease progression. Thousands of clinical trials have evaluated both existing drugs, repurposed for SARS-CoV-2 infection, or drugs that were in development for other diseases.

Initially, medical interventions for hospitalised COVID-19 patients was supportive and aimed to improve oxygenation in the face of infection-induced lung damage. In patients that progressed to acute respiratory distress syndrome (ARDS) this could extend to CPAP, intubation or extracorporeal membrane oxygenation (ECMO; although this is very limited in availability). It soon became apparent that severe COVID-19 might be accompanied by hyper-inflammation and microvascular clotting abnormalities that extended beyond the respiratory system, and that patients could experience rapid deterioration of pulmonary, cardiac, and/or neurological function. This emerging understanding of severe COVID-19 pathology led to the urgent search more targeted treatment options.

The University of Oxford-led “Randomised Evaluation of COVID-19 Therapy” (RECOVERY) trial has been instrumental in identifying therapeutic options for COVID-19 patients. RECOVERY is an international study, and as of April 2022 had provided evidence for 4 drugs that are effective COVID-19 treatments*. This page from the RECOVERY website shows the timeline of discoveries, and also (importantly) indicates some of the drugs that have shown no clinical benefit.

 

Therapies that are host-directed

Dexamethasone* is a widely available and relatively cheap corticosteroid (glucocorticoid receptor agonist) that targets the over-active immune response in patients with severe COVID-19. It has become the primary addition to standard care for critically ill COVID-19 patients.

Tocilizumab* is an anti-IL-6 receptor mAb, with immunosuppressive action that is approved for chronic autoimmune indications. Following many clinical studies, tocilizumab was found to decrease COVID-19 mortality, and in the UK can be used to treat critically ill COVID-19 patients in ICUs. In this setting, it is used in addition to corticosteroid therapy.

Baricitinib* is an oral Janus kinase inhibitor that has powerful anti-inflammatory activity. It is already used to treat severe rheumatoid arthritis, so its safety profile is well established. Baricitinib is indicated for hospitalised COVID-19 patients in addition to standard of care therapies such as immunomodulatory treatments (e.g. dexamethasone, tocilizumab) or the antiviral drug remdesivir.

To date the drugs that have demonstrated clinical benefit that holds up under RCT evaluation are those that modulate the inflammatory component of SARS-CoV-2 infection.

 

Therapies that target the virus

Anti-spike monoclonal antibodies

Several such mAbs were rapidly generated, either via analysis of plasma from recovered COVID-19 patients, and/or other mAb generation/optimisation strategies. A number of these have been authorised in different jurisdictions as COVID-19 therapies. Some are used in combinations, and work is ongoing to determine how effective they are in view of evolving SARS-CoV-2 variants.  Monoclonal antibodies are particularly useful for patients who either cannot be vaccinated or who don’t develop a strong vaccine response.

Regdanvimab is EMA authorised to treat SARS-CoV-2 positive patients with mild-moderate symptoms, who don’t require supplemental oxygen therapy, but who are at increased risk of progressing to severe disease.

Sotrovimab retains activity against the omicron (B.1.1.529) SARS-CoV-2 variant

Casirivimab + imdevimab (Ronapreve*) is a cocktail of two mAbs that have non-overlapping epitopes on the SARS-CoV-2 spike protein. Like regdanvimab, approval indicates Ronapreve use in confirmed COVID-19 patents with mild-moderate disease who are at high risk of progressing to severe disease.

A list of some other anti-spike mAbs is available on the Guide to PHARMACOLOGY

Mpro (main protease; 3CLpro)  inhibitors

Nirmatrelvir is the Mpro inhibitor component of Pfizer’s Paxlovid. Inhibiting Mpro blocks replication at an early stage in the virus' life cycle, so Paxlovid should be administered within 5 days of symptom onset. There is provisional evidence that nirmatrelvir retains activity against SARS-CoV-2 variants including delta and omicron. Paxlovid contains low dose ritonavir to inhibit CYP450-mediated metabolic clearance of nirmatrelvir.

RdRp (RNA-dependent RNA polymerase)  inhibitors

The conservation of RdRP catalytic domain between different RNA virus families means that inhibitors that were designed against other viral pathogens have some activity against the SARS coronaviruses.

One such inhibitor is remdesivir, which is a broad spectrum antiviral that was originally evaluated for anti-Ebola and anti-Marburg virus activity. In vitro activity against SARS and MERS coronaviruses had been demonstrated, so remdesivir was quickly tested for anti-SARS-CoV-2 activity. Anti-SARS-CoV-2 activity in in vitro systems and in animal models is low, and its clinical efficacy is not robust. However remdesivir was the first direct-acting antiviral to be FDA approved for COVID-19 (October 2020), in the rush to address the need for drug treatments for SARS-CoV-2 infections.  

This webpage is regularly updated with best proctice guidelines and a wealth of useful information for clinicians that covers diagnosis, management and follow-up for COVID-19.

No votes yet

Introduction to Antimicrobials

Antibacterial drugs may be grouped according to how they alter bacterial cell function/structure, e.g.

  • nucleic acid precursor synthesis;
  • DNA replication and structure;
  • protein synthesis;
  • cell wall peptidoglycan synthesis;
  • cell membrane integrity

Class II & III reactions in the bacteria are targets for antibacterial drugs since these reactions are unique in bacterial cells. Class II reactions include those responsible for synthesis of molecular building blocks (i.e. precursors of DNA, proteins, etc.). Bacteria rely on synthesis of folate by themselves rather than intake from other sources. Thus, interference with the folate biosynthesis pathway is one mechanism employed by antibacterial drugs. Class III reactions make use of the aforementioned building blocks to replicate DNA, synthesise proteins and cell wall components and maintain cell membrane structure. Mechanisms involved are very different between humans and bacteria, thereby favouring the actions of many antibacterial drugs.

Part of this video (from 5:14 to 8:05), describes different classes of antibiotics with their sites and mechanisms of actions briefly introduced.  This information is useful for the learner to gain an understanding of the different modes of antibacterial drug actions.

Beginner level

Author: Eric Strong/ Strong Medicine

Average: 3 (10 votes)

Aminoglycosides

Aminoglycosides are bactericidal in function, and are named after the amino-modified glycoside (sugar) that is part of their chemical structure. The primary mode of action of aminoglycosides is by inhibition of protein synthesis. Commonly-used drugs in this class include amikacin, gentamicin, neomycin sulfate, streptomycin, and tobramycin. All are bactericidal and active against some Gram-positive and many Gram-negative organisms. Amikacin, gentamicin, and tobramycin are also active against Pseudomonas aeruginosa. Streptomycin is active against Mycobacterium tuberculosis and is now almost entirely reserved for tuberculosis.

This short video (7:11) is part of an introductory series of videos on antibiotic classes produced by Ryan Sheehy of Kansas City University. It uses a narrated animation to introduce you to the basic structure, mechanisms of action and clinical uses of aminoglycosides. Aminoglycosides act by inhibiting bacterial protein synthesis.

Average: 5 (1 vote)

Cephalosporins

Cephalosporins are a class of β-lactam antibiotics derived from the fungus Cephalosporium.  This class of antibiotics works by inhibiting bacterial cell wall synthesis by binding to penicillin binding proteins, causing bacterial cell lysis.  Specific examples of penicillin binding proteins include carboxypeptidases and endopeptidases; these penicillin binding protein enzymes normally form the peptide cross links between peptidoglycans in bacterial cell walls.  However, in the presence of beta-lactam antibiotics, formation of these cross-links is disrupted, the cell wall becomes osmotically unstable, and bacteria burst from osmotic pressure.  Cephalosporins are both bactericidal and time dependent, meaning that they effectively kill susceptible bacteria as long as the plasma concentration of the antibiotic remains above the minimum inhibitory concentration between doses. 

The structures of the agents in this class vary greatly, but they generally share commonalities around a β-lactam ring (e.g. the “square” four membered ring).  In the figure, the functional group R2 determines both the anti-bacterial spectrum coverage and β-lactamase resistance, while R1 determines metabolism and pharmacokinetic parameters of the cephalosporin.

These drugs are renally eliminated and doses must be adjusted when renal dysfunction is present.  The most common adverse reactions to cephalosporins are gastrointestinal upset and an allergic reaction in the form of a rash.  Due to their structural similarities with penicillins, there is a slight chance individuals with penicillin allergies may experience cross-reactivity with cephalosporins.  What was once thought to be a 10% risk of cross-reactivity is now thought to be attributed to cross-contamination during manufacturing processes and is now believed to be closer to 1% with first generation cephalosporins and less likely with other generations.  The third and fourth generation cephalosporins have side chains that generally render them dissimilar enough to penicillins so as to not lead to cross-sensitivity; thus, individuals with a history of hives to penicillins can usually tolerate the newer cephalosporins without any problems.  However, to be on the safe side, in general, all cephalosporins are usually avoided in individuals that report a history of anaphylactic reactions to penicillins.

Resistance to cephalosporins arises via two different mechanisms.  Target-mediated resistance occurs when bacteria have alterations in penicillin binding proteins that reduce a cephalosporin’s affinity for binding to penicillin binding proteins.  Another mechanism of resistance occurs if the bacteria acquire β-lactamase enzymes, known as cephalosporinases, capable of lysing and opening the β-lactam ring, rendering the molecule inactive. 

There are various cephalosporins available on the market today.  They are commonly divided into different groups, called generations, based on the structure of their side chains, and thus their antimicrobial activities.

 

1st Generation Cephalosporins

First generation cephalosporins have good activity against gram-positive bacteria including penicillinase-producing streptococci and staphylococci and modest activity against gram-negative rods such as K. pneumonia, P. mirabilis, and E. coli.  However, they offer no reliable anaerobic coverage.   They, along with some penicillins, are often drugs of choice for methicillin-susceptible Staphylococcus aureus (MSSA).  Agents in this class include cephalexin, cefazolin, and cefadroxil.  Cephalexin is often used orally to treat skin infections and cellulitis. Cefazolin is commonly administered during surgery to prevent infections of the surgical site.    Chemically, cefazolin contains a N-methyl thiotetrazole (NMTT) functional group which has been linked to specific adverse effects.  Specifically, when alcohol is consumed, a disulfiram-like reaction characterized by unpleasant side effects like severe nausea and vomiting can occur when drugs with NMTT side chains are taken.  The NMTT chemical ring also interferes with vitamin K formation and can lead to an increased bleeding risk in some patients. 

 

2nd Generation Cephalosporins

Second generation agents include cefuroxime, cefoxitin, cefotetan, cefprozil, and cefaclor.  As a group, the second generation cephalosporins sacrifice some activity against gram-positive bacteria in favor of gaining more gram-negative coverage.  These drugs possess gram-negative coverage for H. influenza and M. catarrhalis, organisms that commonly cause upper respiratory tract infections as well as coverage for E. coli and other gram negative bacteria that cause uncomplicated urinary tract infections.  The drugs cefoxitin and cefotetan have added benefits of possessing anaerobic coverage for B. fragilis, a cause of intra-abdominal infections.  Cefotetan also has the NMTT functional group mentioned above with cefazolin and may produce a disulfiram-like reaction if alcohol is consumed; this side chain may also increase bleeding risk.  Cefaclor has been associated with a non-allergic rash caused by reactive intermediates that acetylate proteins and produce immunogenic complexes; however, this reaction is not a contraindication to use of other cephalosporins or penicillins.

 

3rd Generation Cephalosporins

Ceftriaxone, cefotaxime, ceftazidime, cefixime, cefpodoxime, cefdinir, and ceftibuten are considered third generation cephalosporins.  Third generation cephalosporins cannot be used to treat staphylococcal or anaerobic infections, but do possess coverage against pneumococcal organisms.  Furthermore, third generation cephalosporins exhibit enhanced gram-negative activity and are useful for treating infections caused by Enterobacteriaceae, Serratia spp., and N. gonorrhea.  Ceftriaxone is often used to treat serious community-acquired pneumonia infections, but since it does not cover pseudomonas, it is not be an appropriate choice for health-care acquired pneumonia.   On the other hand, ceftazidime is a drug of choice for treating infections caused by P. aeruginosa including lung infections.  In the presence of central nervous system inflammation, ceftriaxone and cefotaxime can cross the blood brain barrier and can be used in combination with other drugs to treat meningitis.  Although most third generation drugs are eliminated predominantly by the kidneys, ceftriaxone has dual elimination with the kidneys and liver and can cause pseudocholelithiasis, which is a feeling like a person has a gall stone -- a situation that usually resolves after the medication is stopped.  In addition, ceftriaxone can precipitate in the gall bladder and lead to stone formation; in attempt to avoid this, the drug should never be administered with intravenous calcium.  Due to their relatively broad spectrum against normal gut bacterial flora, the agents in this generation are commonly implicated in causing C. difficile-associated diarrhea.

4th Generation Cephalosporin

Cefepime is considered to be a fourth generation cephalosporin.  It combines the gram-positive coverage of the first generation cephalosporins with the gram-negative coverage of the third generation cephalosporins.  Like ceftazidime of the third generation agents, cefepime lacks anaerobic coverage but is active against P. aeruginosa.  It is the broadest spectrum cephalosporin and is the drug of choice for Enterobacter spp.  Its use is often reserved for empiric treatment in hospitalized patients when coverage for gram-positive organisms, Enterobacteriaceae, or Pseudomonas spp is needed.

Rebecca Kramer, Kelly Karpa

This 12 minute video discusses cephalosporins by generation, including spectrum coverage and clinical uses.

Beginner level.

Author: Roger Seheult, MD

No votes yet

Cephalosporins are a class of β-lactam antibiotics derived from the fungus Cephalosporium.  This class of antibiotics works by inhibiting bacterial cell wall synthesis by binding to penicillin binding proteins, causing bacterial cell lysis.  Specific examples of penicillin binding proteins include carboxypeptidases and endopeptidases; these penicillin binding protein enzymes normally form the peptide cross links between peptidoglycans in bacterial cell walls.  However, in the presence of beta-lactam antibiotics, formation of these cross-links is disrupted, the cell wall becomes osmotically unstable, and bacteria burst from osmotic pressure.  Cephalosporins are both bactericidal and time dependent, meaning that they effectively kill susceptible bacteria as long as the plasma concentration of the antibiotic remains above the minimum inhibitory concentration between doses. 

The structures of the agents in this class vary greatly, but they generally share commonalities around a β-lactam ring (e.g. the “square” four membered ring).  In the figure, the functional group R2 determines both the anti-bacterial spectrum coverage and β-lactamase resistance, while R1 determines metabolism and pharmacokinetic parameters of the cephalosporin.

These drugs are renally eliminated and doses must be adjusted when renal dysfunction is present.  The most common adverse reactions to cephalosporins are gastrointestinal upset and an allergic reaction in the form of a rash.  Due to their structural similarities with penicillins, there is a slight chance individuals with penicillin allergies may experience cross-reactivity with cephalosporins.  What was once thought to be a 10% risk of cross-reactivity is now thought to be attributed to cross-contamination during manufacturing processes and is now believed to be closer to 1% with first generation cephalosporins and less likely with other generations.  The third and fourth generation cephalosporins have side chains that generally render them dissimilar enough to penicillins so as to not lead to cross-sensitivity; thus, individuals with a history of hives to penicillins can usually tolerate the newer cephalosporins without any problems.  However, to be on the safe side, in general, all cephalosporins are usually avoided in individuals that report a history of anaphylactic reactions to penicillins.

Resistance to cephalosporins arises via two different mechanisms.  Target-mediated resistance occurs when bacteria have alterations in penicillin binding proteins that reduce a cephalosporin’s affinity for binding to penicillin binding proteins.  Another mechanism of resistance occurs if the bacteria acquire β-lactamase enzymes, known as cephalosporinases, capable of lysing and opening the β-lactam ring, rendering the molecule inactive. 

There are various cephalosporins available on the market today.  They are commonly divided into different groups, called generations, based on the structure of their side chains, and thus their antimicrobial activities.

 

1st Generation Cephalosporins

First generation cephalosporins have good activity against gram-positive bacteria including penicillinase-producing streptococci and staphylococci and modest activity against gram-negative rods such as K. pneumonia, P. mirabilis, and E. coli.  However, they offer no reliable anaerobic coverage.   They, along with some penicillins, are often drugs of choice for methicillin-susceptible Staphylococcus aureus (MSSA).  Agents in this class include cephalexin, cefazolin, and cefadroxil.  Cephalexin is often used orally to treat skin infections and cellulitis. Cefazolin is commonly administered during surgery to prevent infections of the surgical site.    Chemically, cefazolin contains a N-methyl thiotetrazole (NMTT) functional group which has been linked to specific adverse effects.  Specifically, when alcohol is consumed, a disulfiram-like reaction characterized by unpleasant side effects like severe nausea and vomiting can occur when drugs with NMTT side chains are taken.  The NMTT chemical ring also interferes with vitamin K formation and can lead to an increased bleeding risk in some patients. 

 

2nd Generation Cephalosporins

Second generation agents include cefuroxime, cefoxitin, cefotetan, cefprozil, and cefaclor.  As a group, the second generation cephalosporins sacrifice some activity against gram-positive bacteria in favor of gaining more gram-negative coverage.  These drugs possess gram-negative coverage for H. influenza and M. catarrhalis, organisms that commonly cause upper respiratory tract infections as well as coverage for E. coli and other gram negative bacteria that cause uncomplicated urinary tract infections.  The drugs cefoxitin and cefotetan have added benefits of possessing anaerobic coverage for B. fragilis, a cause of intra-abdominal infections.  Cefotetan also has the NMTT functional group mentioned above with cefazolin and may produce a disulfiram-like reaction if alcohol is consumed; this side chain may also increase bleeding risk.  Cefaclor has been associated with a non-allergic rash caused by reactive intermediates that acetylate proteins and produce immunogenic complexes; however, this reaction is not a contraindication to use of other cephalosporins or penicillins.

 

3rd Generation Cephalosporins

Ceftriaxone, cefotaxime, ceftazidime, cefixime, cefpodoxime, cefdinir, and ceftibuten are considered third generation cephalosporins.  Third generation cephalosporins cannot be used to treat staphylococcal or anaerobic infections, but do possess coverage against pneumococcal organisms.  Furthermore, third generation cephalosporins exhibit enhanced gram-negative activity and are useful for treating infections caused by Enterobacteriaceae, Serratia spp., and N. gonorrhea.  Ceftriaxone is often used to treat serious community-acquired pneumonia infections, but since it does not cover pseudomonas, it is not be an appropriate choice for health-care acquired pneumonia.   On the other hand, ceftazidime is a drug of choice for treating infections caused by P. aeruginosa including lung infections.  In the presence of central nervous system inflammation, ceftriaxone and cefotaxime can cross the blood brain barrier and can be used in combination with other drugs to treat meningitis.  Although most third generation drugs are eliminated predominantly by the kidneys, ceftriaxone has dual elimination with the kidneys and liver and can cause pseudocholelithiasis, which is a feeling like a person has a gall stone -- a situation that usually resolves after the medication is stopped.  In addition, ceftriaxone can precipitate in the gall bladder and lead to stone formation; in attempt to avoid this, the drug should never be administered with intravenous calcium.  Due to their relatively broad spectrum against normal gut bacterial flora, the agents in this generation are commonly implicated in causing C. difficile-associated diarrhea.

4th Generation Cephalosporin

Cefepime is considered to be a fourth generation cephalosporin.  It combines the gram-positive coverage of the first generation cephalosporins with the gram-negative coverage of the third generation cephalosporins.  Like ceftazidime of the third generation agents, cefepime lacks anaerobic coverage but is active against P. aeruginosa.  It is the broadest spectrum cephalosporin and is the drug of choice for Enterobacter spp.  Its use is often reserved for empiric treatment in hospitalized patients when coverage for gram-positive organisms, Enterobacteriaceae, or Pseudomonas spp is needed.

Rebecca Kramer, Kelly Karpa

This 9.5-minute video discusses cephalosporins by generation and individual agents, as well as spectrum of coverage and clinical uses.

Beginner level.

Author: iMedicalSchool

No votes yet

Cephalosporins are a class of β-lactam antibiotics derived from the fungus Cephalosporium.  This class of antibiotics works by inhibiting bacterial cell wall synthesis by binding to penicillin binding proteins, causing bacterial cell lysis.  Specific examples of penicillin binding proteins include carboxypeptidases and endopeptidases; these penicillin binding protein enzymes normally form the peptide cross links between peptidoglycans in bacterial cell walls.  However, in the presence of beta-lactam antibiotics, formation of these cross-links is disrupted, the cell wall becomes osmotically unstable, and bacteria burst from osmotic pressure.  Cephalosporins are both bactericidal and time dependent, meaning that they effectively kill susceptible bacteria as long as the plasma concentration of the antibiotic remains above the minimum inhibitory concentration between doses. 

The structures of the agents in this class vary greatly, but they generally share commonalities around a β-lactam ring (e.g. the “square” four membered ring).  In the figure, the functional group R2 determines both the anti-bacterial spectrum coverage and β-lactamase resistance, while R1 determines metabolism and pharmacokinetic parameters of the cephalosporin.

These drugs are renally eliminated and doses must be adjusted when renal dysfunction is present.  The most common adverse reactions to cephalosporins are gastrointestinal upset and an allergic reaction in the form of a rash.  Due to their structural similarities with penicillins, there is a slight chance individuals with penicillin allergies may experience cross-reactivity with cephalosporins.  What was once thought to be a 10% risk of cross-reactivity is now thought to be attributed to cross-contamination during manufacturing processes and is now believed to be closer to 1% with first generation cephalosporins and less likely with other generations.  The third and fourth generation cephalosporins have side chains that generally render them dissimilar enough to penicillins so as to not lead to cross-sensitivity; thus, individuals with a history of hives to penicillins can usually tolerate the newer cephalosporins without any problems.  However, to be on the safe side, in general, all cephalosporins are usually avoided in individuals that report a history of anaphylactic reactions to penicillins.

Resistance to cephalosporins arises via two different mechanisms.  Target-mediated resistance occurs when bacteria have alterations in penicillin binding proteins that reduce a cephalosporin’s affinity for binding to penicillin binding proteins.  Another mechanism of resistance occurs if the bacteria acquire β-lactamase enzymes, known as cephalosporinases, capable of lysing and opening the β-lactam ring, rendering the molecule inactive. 

There are various cephalosporins available on the market today.  They are commonly divided into different groups, called generations, based on the structure of their side chains, and thus their antimicrobial activities.

 

1st Generation Cephalosporins

First generation cephalosporins have good activity against gram-positive bacteria including penicillinase-producing streptococci and staphylococci and modest activity against gram-negative rods such as K. pneumonia, P. mirabilis, and E. coli.  However, they offer no reliable anaerobic coverage.   They, along with some penicillins, are often drugs of choice for methicillin-susceptible Staphylococcus aureus (MSSA).  Agents in this class include cephalexin, cefazolin, and cefadroxil.  Cephalexin is often used orally to treat skin infections and cellulitis. Cefazolin is commonly administered during surgery to prevent infections of the surgical site.    Chemically, cefazolin contains a N-methyl thiotetrazole (NMTT) functional group which has been linked to specific adverse effects.  Specifically, when alcohol is consumed, a disulfiram-like reaction characterized by unpleasant side effects like severe nausea and vomiting can occur when drugs with NMTT side chains are taken.  The NMTT chemical ring also interferes with vitamin K formation and can lead to an increased bleeding risk in some patients. 

 

2nd Generation Cephalosporins

Second generation agents include cefuroxime, cefoxitin, cefotetan, cefprozil, and cefaclor.  As a group, the second generation cephalosporins sacrifice some activity against gram-positive bacteria in favor of gaining more gram-negative coverage.  These drugs possess gram-negative coverage for H. influenza and M. catarrhalis, organisms that commonly cause upper respiratory tract infections as well as coverage for E. coli and other gram negative bacteria that cause uncomplicated urinary tract infections.  The drugs cefoxitin and cefotetan have added benefits of possessing anaerobic coverage for B. fragilis, a cause of intra-abdominal infections.  Cefotetan also has the NMTT functional group mentioned above with cefazolin and may produce a disulfiram-like reaction if alcohol is consumed; this side chain may also increase bleeding risk.  Cefaclor has been associated with a non-allergic rash caused by reactive intermediates that acetylate proteins and produce immunogenic complexes; however, this reaction is not a contraindication to use of other cephalosporins or penicillins.

 

3rd Generation Cephalosporins

Ceftriaxone, cefotaxime, ceftazidime, cefixime, cefpodoxime, cefdinir, and ceftibuten are considered third generation cephalosporins.  Third generation cephalosporins cannot be used to treat staphylococcal or anaerobic infections, but do possess coverage against pneumococcal organisms.  Furthermore, third generation cephalosporins exhibit enhanced gram-negative activity and are useful for treating infections caused by Enterobacteriaceae, Serratia spp., and N. gonorrhea.  Ceftriaxone is often used to treat serious community-acquired pneumonia infections, but since it does not cover pseudomonas, it is not be an appropriate choice for health-care acquired pneumonia.   On the other hand, ceftazidime is a drug of choice for treating infections caused by P. aeruginosa including lung infections.  In the presence of central nervous system inflammation, ceftriaxone and cefotaxime can cross the blood brain barrier and can be used in combination with other drugs to treat meningitis.  Although most third generation drugs are eliminated predominantly by the kidneys, ceftriaxone has dual elimination with the kidneys and liver and can cause pseudocholelithiasis, which is a feeling like a person has a gall stone -- a situation that usually resolves after the medication is stopped.  In addition, ceftriaxone can precipitate in the gall bladder and lead to stone formation; in attempt to avoid this, the drug should never be administered with intravenous calcium.  Due to their relatively broad spectrum against normal gut bacterial flora, the agents in this generation are commonly implicated in causing C. difficile-associated diarrhea.

4th Generation Cephalosporin

Cefepime is considered to be a fourth generation cephalosporin.  It combines the gram-positive coverage of the first generation cephalosporins with the gram-negative coverage of the third generation cephalosporins.  Like ceftazidime of the third generation agents, cefepime lacks anaerobic coverage but is active against P. aeruginosa.  It is the broadest spectrum cephalosporin and is the drug of choice for Enterobacter spp.  Its use is often reserved for empiric treatment in hospitalized patients when coverage for gram-positive organisms, Enterobacteriaceae, or Pseudomonas spp is needed.

Rebecca Kramer, Kelly Karpa

This learning resource includes links to a set of short videos (all <4 minutes) that are part of an introductory series of videos on antibiotic classes produced by Ryan Sheehy of Kansas City University. They use narrated animation to introduce you to the basic structure, mechanisms of action and resistance, spectrum and adverse effects of the evolving generations cephalosporins.

The 1st generation cephalosporins (including cefazolin and cephalexin among others) inhibit transpeptidase and cell wall synthesis similar the other cephalosporins. The drugs in this generation are active against gram-positive cocci except MRSA, enterococci and Staphylococcus epidermidis. They have modest activity against gram-negative bacteria. The introductory video on cephalosporins (https://www.youtube.com/watch?v=FBnvhZT2TXo) should be viewed before watching these videos.

Second generation cephalosporins

The 2nd generation cephalosporins include cefuroxime, cefaclor, and cefprozil, and the cephamycins cefoxitin and cefotetan among others. This group are generally active against the same organisms as the 1st generation drugs but have expanded gram-negative coverage.

Third generation cephalosporins

The 3rd generation cephalosporins (including cefoxatime and ceftriaxone among others) are more active against gram-negative organisms but they have less activity against gram-positive organisms compared to the 1st generation cephalosporins.

Fourth generation cephalosporins

Cefepime expands the gram-negative coverage of the 3rd generation cephalosporins. It has similar coverage to that of the 3rd generation drug, ceftriaxone, which includes gram-negative and gram-positive organisms.

Fifth generation cephalosporins

The 5th generation cephalosporins, ceftaroline and ceftolozane, are noteworthy for their enhanced effects against methicillin-resistant Staphylococcus aureus and Pseudomonas.

See also Christopher Duplessis, MD, MPH and Nancy Crum-Cianflone, MD, MPH. Ceftaroline: A New Cephalosporin with Activity against Methicillin-Resistant Staphylococcus aureus (MRSA). Clin Med Rev Ther. 2011 Feb 10; 3: a2466. doi:10.4137/CMRT.S1637; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3140339/. This is an article describing the cephalosporin ceftaroline including its coverage against multidrug-resistant strains of bacteria, mechanism of action, and pharmacokinetic and pharmacodynamics properties. Safety and efficacy studies are also discussed along with its low propensity for inducing resistance among bacteria.

Level: Intermediate/advanced

Average: 2.8 (11 votes)

Cephalosporins are a class of β-lactam antibiotics derived from the fungus Cephalosporium.  This class of antibiotics works by inhibiting bacterial cell wall synthesis by binding to penicillin binding proteins, causing bacterial cell lysis.  Specific examples of penicillin binding proteins include carboxypeptidases and endopeptidases; these penicillin binding protein enzymes normally form the peptide cross links between peptidoglycans in bacterial cell walls.  However, in the presence of beta-lactam antibiotics, formation of these cross-links is disrupted, the cell wall becomes osmotically unstable, and bacteria burst from osmotic pressure.  Cephalosporins are both bactericidal and time dependent, meaning that they effectively kill susceptible bacteria as long as the plasma concentration of the antibiotic remains above the minimum inhibitory concentration between doses. 

The structures of the agents in this class vary greatly, but they generally share commonalities around a β-lactam ring (e.g. the “square” four membered ring).  In the figure, the functional group R2 determines both the anti-bacterial spectrum coverage and β-lactamase resistance, while R1 determines metabolism and pharmacokinetic parameters of the cephalosporin.

These drugs are renally eliminated and doses must be adjusted when renal dysfunction is present.  The most common adverse reactions to cephalosporins are gastrointestinal upset and an allergic reaction in the form of a rash.  Due to their structural similarities with penicillins, there is a slight chance individuals with penicillin allergies may experience cross-reactivity with cephalosporins.  What was once thought to be a 10% risk of cross-reactivity is now thought to be attributed to cross-contamination during manufacturing processes and is now believed to be closer to 1% with first generation cephalosporins and less likely with other generations.  The third and fourth generation cephalosporins have side chains that generally render them dissimilar enough to penicillins so as to not lead to cross-sensitivity; thus, individuals with a history of hives to penicillins can usually tolerate the newer cephalosporins without any problems.  However, to be on the safe side, in general, all cephalosporins are usually avoided in individuals that report a history of anaphylactic reactions to penicillins.

Resistance to cephalosporins arises via two different mechanisms.  Target-mediated resistance occurs when bacteria have alterations in penicillin binding proteins that reduce a cephalosporin’s affinity for binding to penicillin binding proteins.  Another mechanism of resistance occurs if the bacteria acquire β-lactamase enzymes, known as cephalosporinases, capable of lysing and opening the β-lactam ring, rendering the molecule inactive. 

There are various cephalosporins available on the market today.  They are commonly divided into different groups, called generations, based on the structure of their side chains, and thus their antimicrobial activities.

 

1st Generation Cephalosporins

First generation cephalosporins have good activity against gram-positive bacteria including penicillinase-producing streptococci and staphylococci and modest activity against gram-negative rods such as K. pneumonia, P. mirabilis, and E. coli.  However, they offer no reliable anaerobic coverage.   They, along with some penicillins, are often drugs of choice for methicillin-susceptible Staphylococcus aureus (MSSA).  Agents in this class include cephalexin, cefazolin, and cefadroxil.  Cephalexin is often used orally to treat skin infections and cellulitis. Cefazolin is commonly administered during surgery to prevent infections of the surgical site.    Chemically, cefazolin contains a N-methyl thiotetrazole (NMTT) functional group which has been linked to specific adverse effects.  Specifically, when alcohol is consumed, a disulfiram-like reaction characterized by unpleasant side effects like severe nausea and vomiting can occur when drugs with NMTT side chains are taken.  The NMTT chemical ring also interferes with vitamin K formation and can lead to an increased bleeding risk in some patients. 

 

2nd Generation Cephalosporins

Second generation agents include cefuroxime, cefoxitin, cefotetan, cefprozil, and cefaclor.  As a group, the second generation cephalosporins sacrifice some activity against gram-positive bacteria in favor of gaining more gram-negative coverage.  These drugs possess gram-negative coverage for H. influenza and M. catarrhalis, organisms that commonly cause upper respiratory tract infections as well as coverage for E. coli and other gram negative bacteria that cause uncomplicated urinary tract infections.  The drugs cefoxitin and cefotetan have added benefits of possessing anaerobic coverage for B. fragilis, a cause of intra-abdominal infections.  Cefotetan also has the NMTT functional group mentioned above with cefazolin and may produce a disulfiram-like reaction if alcohol is consumed; this side chain may also increase bleeding risk.  Cefaclor has been associated with a non-allergic rash caused by reactive intermediates that acetylate proteins and produce immunogenic complexes; however, this reaction is not a contraindication to use of other cephalosporins or penicillins.

 

3rd Generation Cephalosporins

Ceftriaxone, cefotaxime, ceftazidime, cefixime, cefpodoxime, cefdinir, and ceftibuten are considered third generation cephalosporins.  Third generation cephalosporins cannot be used to treat staphylococcal or anaerobic infections, but do possess coverage against pneumococcal organisms.  Furthermore, third generation cephalosporins exhibit enhanced gram-negative activity and are useful for treating infections caused by Enterobacteriaceae, Serratia spp., and N. gonorrhea.  Ceftriaxone is often used to treat serious community-acquired pneumonia infections, but since it does not cover pseudomonas, it is not be an appropriate choice for health-care acquired pneumonia.   On the other hand, ceftazidime is a drug of choice for treating infections caused by P. aeruginosa including lung infections.  In the presence of central nervous system inflammation, ceftriaxone and cefotaxime can cross the blood brain barrier and can be used in combination with other drugs to treat meningitis.  Although most third generation drugs are eliminated predominantly by the kidneys, ceftriaxone has dual elimination with the kidneys and liver and can cause pseudocholelithiasis, which is a feeling like a person has a gall stone -- a situation that usually resolves after the medication is stopped.  In addition, ceftriaxone can precipitate in the gall bladder and lead to stone formation; in attempt to avoid this, the drug should never be administered with intravenous calcium.  Due to their relatively broad spectrum against normal gut bacterial flora, the agents in this generation are commonly implicated in causing C. difficile-associated diarrhea.

4th Generation Cephalosporin

Cefepime is considered to be a fourth generation cephalosporin.  It combines the gram-positive coverage of the first generation cephalosporins with the gram-negative coverage of the third generation cephalosporins.  Like ceftazidime of the third generation agents, cefepime lacks anaerobic coverage but is active against P. aeruginosa.  It is the broadest spectrum cephalosporin and is the drug of choice for Enterobacter spp.  Its use is often reserved for empiric treatment in hospitalized patients when coverage for gram-positive organisms, Enterobacteriaceae, or Pseudomonas spp is needed.

Rebecca Kramer, Kelly Karpa

This 7 minute video showcases bacterial cell wall synthesis, the mechanism of action of cephalosporins (starting at 2:33), and the mechanisms by which bacteria develop resistance to cephalosporins (starting at 3:38). 

Intermediate level.

Author: Mechanisms in Medicine

Average: 3 (1 vote)

Cephalosporins are a class of β-lactam antibiotics derived from the fungus Cephalosporium.  This class of antibiotics works by inhibiting bacterial cell wall synthesis by binding to penicillin binding proteins, causing bacterial cell lysis.  Specific examples of penicillin binding proteins include carboxypeptidases and endopeptidases; these penicillin binding protein enzymes normally form the peptide cross links between peptidoglycans in bacterial cell walls.  However, in the presence of beta-lactam antibiotics, formation of these cross-links is disrupted, the cell wall becomes osmotically unstable, and bacteria burst from osmotic pressure.  Cephalosporins are both bactericidal and time dependent, meaning that they effectively kill susceptible bacteria as long as the plasma concentration of the antibiotic remains above the minimum inhibitory concentration between doses. 

The structures of the agents in this class vary greatly, but they generally share commonalities around a β-lactam ring (e.g. the “square” four membered ring).  In the figure, the functional group R2 determines both the anti-bacterial spectrum coverage and β-lactamase resistance, while R1 determines metabolism and pharmacokinetic parameters of the cephalosporin.

These drugs are renally eliminated and doses must be adjusted when renal dysfunction is present.  The most common adverse reactions to cephalosporins are gastrointestinal upset and an allergic reaction in the form of a rash.  Due to their structural similarities with penicillins, there is a slight chance individuals with penicillin allergies may experience cross-reactivity with cephalosporins.  What was once thought to be a 10% risk of cross-reactivity is now thought to be attributed to cross-contamination during manufacturing processes and is now believed to be closer to 1% with first generation cephalosporins and less likely with other generations.  The third and fourth generation cephalosporins have side chains that generally render them dissimilar enough to penicillins so as to not lead to cross-sensitivity; thus, individuals with a history of hives to penicillins can usually tolerate the newer cephalosporins without any problems.  However, to be on the safe side, in general, all cephalosporins are usually avoided in individuals that report a history of anaphylactic reactions to penicillins.

Resistance to cephalosporins arises via two different mechanisms.  Target-mediated resistance occurs when bacteria have alterations in penicillin binding proteins that reduce a cephalosporin’s affinity for binding to penicillin binding proteins.  Another mechanism of resistance occurs if the bacteria acquire β-lactamase enzymes, known as cephalosporinases, capable of lysing and opening the β-lactam ring, rendering the molecule inactive. 

There are various cephalosporins available on the market today.  They are commonly divided into different groups, called generations, based on the structure of their side chains, and thus their antimicrobial activities.

 

1st Generation Cephalosporins

First generation cephalosporins have good activity against gram-positive bacteria including penicillinase-producing streptococci and staphylococci and modest activity against gram-negative rods such as K. pneumonia, P. mirabilis, and E. coli.  However, they offer no reliable anaerobic coverage.   They, along with some penicillins, are often drugs of choice for methicillin-susceptible Staphylococcus aureus (MSSA).  Agents in this class include cephalexin, cefazolin, and cefadroxil.  Cephalexin is often used orally to treat skin infections and cellulitis. Cefazolin is commonly administered during surgery to prevent infections of the surgical site.    Chemically, cefazolin contains a N-methyl thiotetrazole (NMTT) functional group which has been linked to specific adverse effects.  Specifically, when alcohol is consumed, a disulfiram-like reaction characterized by unpleasant side effects like severe nausea and vomiting can occur when drugs with NMTT side chains are taken.  The NMTT chemical ring also interferes with vitamin K formation and can lead to an increased bleeding risk in some patients. 

 

2nd Generation Cephalosporins

Second generation agents include cefuroxime, cefoxitin, cefotetan, cefprozil, and cefaclor.  As a group, the second generation cephalosporins sacrifice some activity against gram-positive bacteria in favor of gaining more gram-negative coverage.  These drugs possess gram-negative coverage for H. influenza and M. catarrhalis, organisms that commonly cause upper respiratory tract infections as well as coverage for E. coli and other gram negative bacteria that cause uncomplicated urinary tract infections.  The drugs cefoxitin and cefotetan have added benefits of possessing anaerobic coverage for B. fragilis, a cause of intra-abdominal infections.  Cefotetan also has the NMTT functional group mentioned above with cefazolin and may produce a disulfiram-like reaction if alcohol is consumed; this side chain may also increase bleeding risk.  Cefaclor has been associated with a non-allergic rash caused by reactive intermediates that acetylate proteins and produce immunogenic complexes; however, this reaction is not a contraindication to use of other cephalosporins or penicillins.

 

3rd Generation Cephalosporins

Ceftriaxone, cefotaxime, ceftazidime, cefixime, cefpodoxime, cefdinir, and ceftibuten are considered third generation cephalosporins.  Third generation cephalosporins cannot be used to treat staphylococcal or anaerobic infections, but do possess coverage against pneumococcal organisms.  Furthermore, third generation cephalosporins exhibit enhanced gram-negative activity and are useful for treating infections caused by Enterobacteriaceae, Serratia spp., and N. gonorrhea.  Ceftriaxone is often used to treat serious community-acquired pneumonia infections, but since it does not cover pseudomonas, it is not be an appropriate choice for health-care acquired pneumonia.   On the other hand, ceftazidime is a drug of choice for treating infections caused by P. aeruginosa including lung infections.  In the presence of central nervous system inflammation, ceftriaxone and cefotaxime can cross the blood brain barrier and can be used in combination with other drugs to treat meningitis.  Although most third generation drugs are eliminated predominantly by the kidneys, ceftriaxone has dual elimination with the kidneys and liver and can cause pseudocholelithiasis, which is a feeling like a person has a gall stone -- a situation that usually resolves after the medication is stopped.  In addition, ceftriaxone can precipitate in the gall bladder and lead to stone formation; in attempt to avoid this, the drug should never be administered with intravenous calcium.  Due to their relatively broad spectrum against normal gut bacterial flora, the agents in this generation are commonly implicated in causing C. difficile-associated diarrhea.

4th Generation Cephalosporin

Cefepime is considered to be a fourth generation cephalosporin.  It combines the gram-positive coverage of the first generation cephalosporins with the gram-negative coverage of the third generation cephalosporins.  Like ceftazidime of the third generation agents, cefepime lacks anaerobic coverage but is active against P. aeruginosa.  It is the broadest spectrum cephalosporin and is the drug of choice for Enterobacter spp.  Its use is often reserved for empiric treatment in hospitalized patients when coverage for gram-positive organisms, Enterobacteriaceae, or Pseudomonas spp is needed.

Rebecca Kramer, Kelly Karpa

This article provides a more in-depth overview of cephalosporins, broken down by their generation.  Their mechanism of action, adverse effects, spectrum of activity, and clinical use are discussed in detail.  It also provides resources for further reading on cephalosporins. 

Intermediate level.

Author: eMedExpert

No votes yet

Glycopeptide and lipoglycopeptide antibiotics

The glycopeptide and lipoglycopeptide antibiotics target the bacterial cell wall, but with a mechanism that is distinct from those of the β-lactams and cephalosporins.

Glycopeptide antibiotics inhibit the bacterial peptidoglycan glycosyltransferase enzyme, thus blocking biosynthesis of the peptidoglycans that are required for cell wall formation. They exhibit a narrow spectrum of activity, principally against Gram-positive enterococci. Glycopeptide antibiotics are relatively toxic in humans, so their use should be restricted to critically ill patients who are allergic to β-lactams, or whose infections are caused by β-lactam-resistant organisms.

Vancomycin has been available for clinical use since 1964 (in the US). Oral vancomycin is indicated as a treatment for Clostridium difficile colitis and Staphylococcal infections of the colon and small intestines. A parenteral formulation is available to treat serious infections outside of the intestines. Identification of strains of Staphylococcus aureus that are vancomycin-resistant (VRSA) began in 2002.

Teicoplanin's  spectrum of activity is similar to that of vancomycin, with activity against Gram-positive bacteria including Staphylococci and Clostridium spp.

Telavancin is a vancomycin derivative, in clinical use since 2009 (US).

Glycopeptides had typically been used as the last effective line of defense against MRSA, but newer classes of antibiotics have proven to have activity against MRSA,  including linezolid (an oxazolidinone antibiotic), and daptomycin (a lipopeptide antibiotic).

Lipoglycopeptides are a class of antibiotic that as their name suggests, have lipophilic side-chains linked to glycopeptides. Oritavancin, telavancin and dalbavancin are examples of this class that are approved for clinical use. In addition to disrupting cell wall biosynthesis, oritavancin and telavancin directly disrupt the cell wall, which improves their bactericidal activity compared to the glycopeptide class drugs.

All of the lipoglycopeptide antibiotics are administered by injection, and have proven particularly useful for the treatment of complicated skin and skin structure infections, including those caused by MRSA and Streptococcus pyogenes.

 

This 5 minute animated video provides an introduction to the mechanism and use of glycopeptide and lipoglycopeptide antibiotics. It was produced by Ryan Sheehy, and is aimed at entry level learners.

No votes yet

Macrolides, ketolides, lincosamides and straptogramins

This group of antibacterials share their mechanism of action- disrupting function of the bacterial 50S ribosomal subunit and inhibiting protein synthesis.

Macrolides consist of a large lactone ring with several deoxy sugars. Erythromycin and clarithromycin are representative examples. These drugs bind to the 50S subunit, near the peptidyltransferase centre (PTC). Therefore, the growing peptide cannot “lean over” and is kept in the A site. The subsequent events, i.e. the shifting of the “uncharged” tRNA to E site and ribosomal sliding movement, will not occur. GI disturbances and rash are common. There are rare occurrences of cholestatic hepatitis. Erythromycin is also a P450 inhibitor. One use of erythromycin is against S. pneumoniae if there is penicillin allergy. Common mechanisms of resistance to macrolides include decreased drug permeability, active drug efflux and most important of all, ribosomal alteration. The 50S ribosomal subunit is methylated, and this affects not only macrolide binding but also that of lincosamides (i.e. clindamycin) and streptogramins. This type of resistance is therefore referred to as MLS B-type resistance. The MLS B-type resistance is widespread across many bacterial species.

Telithromycin is a ketolide based on macrolides, but with a ketone and carbamate group. The ketone group decreases its susceptibility to MLS B-type resistance and active drug efflux while the carbamate group increases binding strength to ribosome. Antibacterial spectrum of telithromycin is similar to macrolides, but with better potency. However, potentially fatal hepatoxicity has limited its use, and in some jurisdictions its use has been withdrawn. 

Streptogramins include pristinamycin, quinupristin/dalfopristin and virginiamycin. These are effective in the treatment of multidrug-resistant bacteria such as vancomycin-resistant Staphylococcus aureus (VRSA) and vancomycin-resistant Enterococcus (VRE).

Dr Willmann Liang

This short video (7:16) is part of an introductory series of videos on antibiotic classes produced by Ryan Sheehy of Kansas City University. It uses a narrated animation to introduce you to the basic structure and mechanisms of action of macrolide and related ketolide antibiotics. It is suitable for beginners.

No votes yet

This group of antibacterials share their mechanism of action- disrupting function of the bacterial 50S ribosomal subunit and inhibiting protein synthesis.

Macrolides consist of a large lactone ring with several deoxy sugars. Erythromycin and clarithromycin are representative examples. These drugs bind to the 50S subunit, near the peptidyltransferase centre (PTC). Therefore, the growing peptide cannot “lean over” and is kept in the A site. The subsequent events, i.e. the shifting of the “uncharged” tRNA to E site and ribosomal sliding movement, will not occur. GI disturbances and rash are common. There are rare occurrences of cholestatic hepatitis. Erythromycin is also a P450 inhibitor. One use of erythromycin is against S. pneumoniae if there is penicillin allergy. Common mechanisms of resistance to macrolides include decreased drug permeability, active drug efflux and most important of all, ribosomal alteration. The 50S ribosomal subunit is methylated, and this affects not only macrolide binding but also that of lincosamides (i.e. clindamycin) and streptogramins. This type of resistance is therefore referred to as MLS B-type resistance. The MLS B-type resistance is widespread across many bacterial species.

Telithromycin is a ketolide based on macrolides, but with a ketone and carbamate group. The ketone group decreases its susceptibility to MLS B-type resistance and active drug efflux while the carbamate group increases binding strength to ribosome. Antibacterial spectrum of telithromycin is similar to macrolides, but with better potency. However, potentially fatal hepatoxicity has limited its use, and in some jurisdictions its use has been withdrawn. 

Streptogramins include pristinamycin, quinupristin/dalfopristin and virginiamycin. These are effective in the treatment of multidrug-resistant bacteria such as vancomycin-resistant Staphylococcus aureus (VRSA) and vancomycin-resistant Enterococcus (VRE).

Dr Willmann Liang

This short video (3:30) is part of an introductory series of videos on antibiotic classes produced by Ryan Sheehy of Kansas City University. It uses a narrated animation to introduce you to the basic structure and mechanisms of action of streptogramin antibiotics. It is suitable for beginners.

No votes yet

This group of antibacterials share their mechanism of action- disrupting function of the bacterial 50S ribosomal subunit and inhibiting protein synthesis.

Macrolides consist of a large lactone ring with several deoxy sugars. Erythromycin and clarithromycin are representative examples. These drugs bind to the 50S subunit, near the peptidyltransferase centre (PTC). Therefore, the growing peptide cannot “lean over” and is kept in the A site. The subsequent events, i.e. the shifting of the “uncharged” tRNA to E site and ribosomal sliding movement, will not occur. GI disturbances and rash are common. There are rare occurrences of cholestatic hepatitis. Erythromycin is also a P450 inhibitor. One use of erythromycin is against S. pneumoniae if there is penicillin allergy. Common mechanisms of resistance to macrolides include decreased drug permeability, active drug efflux and most important of all, ribosomal alteration. The 50S ribosomal subunit is methylated, and this affects not only macrolide binding but also that of lincosamides (i.e. clindamycin) and streptogramins. This type of resistance is therefore referred to as MLS B-type resistance. The MLS B-type resistance is widespread across many bacterial species.

Telithromycin is a ketolide based on macrolides, but with a ketone and carbamate group. The ketone group decreases its susceptibility to MLS B-type resistance and active drug efflux while the carbamate group increases binding strength to ribosome. Antibacterial spectrum of telithromycin is similar to macrolides, but with better potency. However, potentially fatal hepatoxicity has limited its use, and in some jurisdictions its use has been withdrawn. 

Streptogramins include pristinamycin, quinupristin/dalfopristin and virginiamycin. These are effective in the treatment of multidrug-resistant bacteria such as vancomycin-resistant Staphylococcus aureus (VRSA) and vancomycin-resistant Enterococcus (VRE).

Dr Willmann Liang

This narrated video gives an overview of the mechanisms of action of antibiotics that act at the bacterial ribosomes, thus inhibiting bacterial protein synthesis.  Macrolides are introduced at 3:36 of the video.  Mechanisms of drug resistance are also briefly introduced, the erm gene being notable example of the MLS B-type resistance.

Intermediate level 

Author: MedLecturesMadeEasy

No votes yet

This group of antibacterials share their mechanism of action- disrupting function of the bacterial 50S ribosomal subunit and inhibiting protein synthesis.

Macrolides consist of a large lactone ring with several deoxy sugars. Erythromycin and clarithromycin are representative examples. These drugs bind to the 50S subunit, near the peptidyltransferase centre (PTC). Therefore, the growing peptide cannot “lean over” and is kept in the A site. The subsequent events, i.e. the shifting of the “uncharged” tRNA to E site and ribosomal sliding movement, will not occur. GI disturbances and rash are common. There are rare occurrences of cholestatic hepatitis. Erythromycin is also a P450 inhibitor. One use of erythromycin is against S. pneumoniae if there is penicillin allergy. Common mechanisms of resistance to macrolides include decreased drug permeability, active drug efflux and most important of all, ribosomal alteration. The 50S ribosomal subunit is methylated, and this affects not only macrolide binding but also that of lincosamides (i.e. clindamycin) and streptogramins. This type of resistance is therefore referred to as MLS B-type resistance. The MLS B-type resistance is widespread across many bacterial species.

Telithromycin is a ketolide based on macrolides, but with a ketone and carbamate group. The ketone group decreases its susceptibility to MLS B-type resistance and active drug efflux while the carbamate group increases binding strength to ribosome. Antibacterial spectrum of telithromycin is similar to macrolides, but with better potency. However, potentially fatal hepatoxicity has limited its use, and in some jurisdictions its use has been withdrawn. 

Streptogramins include pristinamycin, quinupristin/dalfopristin and virginiamycin. These are effective in the treatment of multidrug-resistant bacteria such as vancomycin-resistant Staphylococcus aureus (VRSA) and vancomycin-resistant Enterococcus (VRE).

Dr Willmann Liang

The first part of this narrated video describes the mechanisms of action of macrolides.  From 3:05 onward, mechanisms of resistance to macrolides are introduced.  Specific reference is made to the erm gene, efflux pumps.

Advanced level.

Author: Mechanisms in Medicine

No votes yet

This group of antibacterials share their mechanism of action- disrupting function of the bacterial 50S ribosomal subunit and inhibiting protein synthesis.

Macrolides consist of a large lactone ring with several deoxy sugars. Erythromycin and clarithromycin are representative examples. These drugs bind to the 50S subunit, near the peptidyltransferase centre (PTC). Therefore, the growing peptide cannot “lean over” and is kept in the A site. The subsequent events, i.e. the shifting of the “uncharged” tRNA to E site and ribosomal sliding movement, will not occur. GI disturbances and rash are common. There are rare occurrences of cholestatic hepatitis. Erythromycin is also a P450 inhibitor. One use of erythromycin is against S. pneumoniae if there is penicillin allergy. Common mechanisms of resistance to macrolides include decreased drug permeability, active drug efflux and most important of all, ribosomal alteration. The 50S ribosomal subunit is methylated, and this affects not only macrolide binding but also that of lincosamides (i.e. clindamycin) and streptogramins. This type of resistance is therefore referred to as MLS B-type resistance. The MLS B-type resistance is widespread across many bacterial species.

Telithromycin is a ketolide based on macrolides, but with a ketone and carbamate group. The ketone group decreases its susceptibility to MLS B-type resistance and active drug efflux while the carbamate group increases binding strength to ribosome. Antibacterial spectrum of telithromycin is similar to macrolides, but with better potency. However, potentially fatal hepatoxicity has limited its use, and in some jurisdictions its use has been withdrawn. 

Streptogramins include pristinamycin, quinupristin/dalfopristin and virginiamycin. These are effective in the treatment of multidrug-resistant bacteria such as vancomycin-resistant Staphylococcus aureus (VRSA) and vancomycin-resistant Enterococcus (VRE).

Dr Willmann Liang

This article provides an overview of the general pharmacology of macrolides.  Important unwanted effects are described in great detail.  With respect to resistance mechanisms, the more susceptible typical macrolides (e.g. azithromycin and clarithromycin) are compared with the more superior telithromycin.

Advanced level

Author: Amy L Graziani

Note that Institutional subscription may be required to access UpToDate.com articles.

No votes yet

Monobactam antibiotics

This class of antibiotics are monocyclic, bacterially-produced β-lactam compounds, but unlike the majority of other β-lactams their β-lactam component is not fused to another ring.

The antibacterial activity of the monobactams is restricted to aerobic Gram-negative bacteria.

Aztreonam is a clinically used monobactam. Indications include severe infections of the blood, urinary tract, lungs, skin, stomach, or female reproductive organs.

This short (3:16) animated video was produced by Ryan Sheehy. It describes the mechanism of action of monobactam antibiotics and their clinical particulars in more detail. It is suitable for beginners.

No votes yet

Oxazolidinone antibiotics

Oxazolidinone antibiotics block an early, initiating step in bacterial protein synthesis. They prevent N-formylmethionyl-tRNAs from binding to the ribosome.

Linezolid is available in intravenous and oral formulations.

Tedizolid is approved for the treatment of acute skin infections

There are additional oxazolidinones in clinical development: contezolid, radezolid

The first oxazolidinone to be used in clinical practice was cycloserine. It has been used as a second line drug to treat tuberculosis since the mid-1950s. Although structurally cycloserine belongs to the oxazolidinones, it has a different mechanism of action and significantly different properties from the other oxazolidinone drugs.

This short 6 minute, introductory, animated video by Ryan Sheehy describes the structure, function and use of oxazolidinone antibiotics in more detail. It is suitable for beginners.

No votes yet

Penicillins and other β-lactam antibiotics

β-lactam antibiotics are so-called because they all contain a β-lactam ring in their chemical structures. In general these antibiotics act to inhibit bacterial wall synthesis. They are broad-spectrum antibiotics with activity against both Gram +ve and Gram -ve bacterial strains.

Subgroups include: penicillin derivatives (penams) and carbapenems which are discussed in more detail below, cephalosporins (cephems), monobactams, and carbacephems (which are reviewed more extensively in other topics within this Drugs for Infections module.

Bacteria can produce β-lactamase as a mechanism of acquired resistance to β-lactam antibiotics. Co-administration of β-lactamase inhibitors can partially mitigate resistance. This short introductory animated video by Ryan Sheehy describes β-lactamase inhibitors in more detail-  Betalactamse inhibitors YouTube video

β-lactamase-sensitive penicillins

Ampicillin is inactivated by penicillinases. Since the majority of staphylococci and E. coli strains and some Haemophilus influenzae strains are now resistant to ampicillin, it should not be used in the hospital setting or without first considering the likelihood of resistance. The main indications for ampicillin treatment are exacerbations of chronic bronchitis and middle ear infections due to Streptococcus pneumoniae and H. influenzae, and for urinary-tract infections.

A fixed-dose combination of ampicillin plus flucloxacillin (co-fluampicil) is available to treat streptococci or staphylococci infections such as cellulitis.

Amoxicillin, a derivative of ampicillin with improved oral absorption, has a similar antibacterial spectrum. It is notably used for the treatment of Lyme disease.

Co-amoxiclav (amoxicillin + clavulanic acid) is active against β-lactamase-producing bacteria that are resistant to amoxicillin, such as resistant strains of Staph. aureus, E. coli, and H. influenzae, as well as many Bacteroides and Klebsiella spp. Its use should be restricted to the treatment of infections likely, or known, to be caused by amoxicillin-resistant β-lactamase producing bacterial strains.

Benzylpenicillin (Penicillin G) is inactivated by gastric acid so has to be delivered by injection. It is effective against many streptococcal (including pneumococcal), gonococcal, and meningococcal infections, anthrax, diphtheria, gas-gangrene, and leptospirosis. Some pneumococci, meningococci, and gonococci strains are less sensitive to benzylpenicillin. Although benzylpenicillin is active against tetanus, treatment with metronidazole is the preferred option. Benzathine benzylpenicillin is given by intramuscular injection to treat early syphilis and late latent syphilis.

Phenoxymethylpenicillin (Penicillin V) is similarly active to benzylpenicillin but is acid-resistant, so can be delivered orally. The principal indications for its use are respiratory-tract infections in children, streptococcal tonsillitis, and for continuing benzylpenicillin-initiated treatment when clinical response has begun. Phenoxymethylpenicillin should not be used for meningococcal or gonococcal infections.

Penicillinase- and β-lactamase-resistant penicillins

Flucloxacillin is not inactivated by penicillinases so it is effective against infections caused by penicillin-resistant staphylococci, and this is its principal use. It is acid-resistant and orally active.

Temocillin is stable against a wide range of β-lactamases. Its use should be reserved for the treatment of infections caused by β-lactamase-producing strains of Gram -ve bacteria, including those that are resistant to third-generation cephalosporins. Temocillin is not active against Pseudomonas aeruginosa or Acinetobacter spp.

This short, introductory animated video by Ryan Sheehy describes penicillinase resistant penicillins - Penicillinase resistant penicillins YouTube video.

Carbapenems

Ertapenem, and the antipseudomonals doripenem, imipenem and meropenem are in this subgroup of β-lactams, and their use is generally reserved for known or suspected multidrug-resistant (MDR) bacterial infections. increasing rates of resistance to carbapenems is a clinical problem, as there are limited options that are effective against carbapenem-resistant bacteria (e.g. Klebsiella pneumoniae and other carbapenem-resistant Enterobacteriaceae).

 

Antipseudomonal penicillins

Piperacillin (a ureidopenicillin) is only available in a fixed-dose combination with the β-lactamase inhibitor tazobactam.

Ticarcillin (a carboxypenicillin) is only available in a fixed-dose combination with β-lactamase inhibiting clavulanic acid.

Both of these preparations are broad spectrum antibiotics that are effective against a range of Gram +ve , Gram -ve bacteria, and anaerobic bacteria. Piperacillin + tazobactam is active against a wider range of Gram -ve organisms than ticarcillin + clavulanic acid and it is more active against Pseudomonas aeruginosa. Neither of these antibacterials combat MRSA. They are typically used to treat septicaemia, hospital-acquired pneumonia, and complicated infections involving the urinary tract, skin and soft tissues, or intra-abdomen. Co-administration of an aminoglycoside (e.g. gentamicin) with these antipseudomonal penicillin preparations effectively combats severe pseudomonas infections.

This short video (4:32) is part of an introductory series of videos on antibiotic classes produced by Ryan Sheehy of Kansas City University. It uses a narrated animation to introduce you to the basic structure and mechanisms of action of penicillins, and mechanisms of antimicrobial resistance to penicillins. Penicillins are beta-lactam antibiotics which interfere with the synthesis of the bacterial cell wall peptidoglycan. They do this by inhibiting penicillin binding proteins, transpeptidase enzymes  that normally crosslink the peptide chains attached to the backbone of the peptidoglycan. Inhibition of this crosslinking by penicillins leads to a lack of cell wall rigidity and bacterial cell death. Bacteria can produce β-lactamase as a mechanism of acquired resistance to β-lactam antibiotics. Other mechanisms of resistance such as alterations of porins are discussed. Videos that follow discuss specific penicillin drug classes.

No votes yet

β-lactam antibiotics are so-called because they all contain a β-lactam ring in their chemical structures. In general these antibiotics act to inhibit bacterial wall synthesis. They are broad-spectrum antibiotics with activity against both Gram +ve and Gram -ve bacterial strains.

Subgroups include: penicillin derivatives (penams) and carbapenems which are discussed in more detail below, cephalosporins (cephems), monobactams, and carbacephems (which are reviewed more extensively in other topics within this Drugs for Infections module.

Bacteria can produce β-lactamase as a mechanism of acquired resistance to β-lactam antibiotics. Co-administration of β-lactamase inhibitors can partially mitigate resistance. This short introductory animated video by Ryan Sheehy describes β-lactamase inhibitors in more detail-  Betalactamse inhibitors YouTube video

β-lactamase-sensitive penicillins

Ampicillin is inactivated by penicillinases. Since the majority of staphylococci and E. coli strains and some Haemophilus influenzae strains are now resistant to ampicillin, it should not be used in the hospital setting or without first considering the likelihood of resistance. The main indications for ampicillin treatment are exacerbations of chronic bronchitis and middle ear infections due to Streptococcus pneumoniae and H. influenzae, and for urinary-tract infections.

A fixed-dose combination of ampicillin plus flucloxacillin (co-fluampicil) is available to treat streptococci or staphylococci infections such as cellulitis.

Amoxicillin, a derivative of ampicillin with improved oral absorption, has a similar antibacterial spectrum. It is notably used for the treatment of Lyme disease.

Co-amoxiclav (amoxicillin + clavulanic acid) is active against β-lactamase-producing bacteria that are resistant to amoxicillin, such as resistant strains of Staph. aureus, E. coli, and H. influenzae, as well as many Bacteroides and Klebsiella spp. Its use should be restricted to the treatment of infections likely, or known, to be caused by amoxicillin-resistant β-lactamase producing bacterial strains.

Benzylpenicillin (Penicillin G) is inactivated by gastric acid so has to be delivered by injection. It is effective against many streptococcal (including pneumococcal), gonococcal, and meningococcal infections, anthrax, diphtheria, gas-gangrene, and leptospirosis. Some pneumococci, meningococci, and gonococci strains are less sensitive to benzylpenicillin. Although benzylpenicillin is active against tetanus, treatment with metronidazole is the preferred option. Benzathine benzylpenicillin is given by intramuscular injection to treat early syphilis and late latent syphilis.

Phenoxymethylpenicillin (Penicillin V) is similarly active to benzylpenicillin but is acid-resistant, so can be delivered orally. The principal indications for its use are respiratory-tract infections in children, streptococcal tonsillitis, and for continuing benzylpenicillin-initiated treatment when clinical response has begun. Phenoxymethylpenicillin should not be used for meningococcal or gonococcal infections.

Penicillinase- and β-lactamase-resistant penicillins

Flucloxacillin is not inactivated by penicillinases so it is effective against infections caused by penicillin-resistant staphylococci, and this is its principal use. It is acid-resistant and orally active.

Temocillin is stable against a wide range of β-lactamases. Its use should be reserved for the treatment of infections caused by β-lactamase-producing strains of Gram -ve bacteria, including those that are resistant to third-generation cephalosporins. Temocillin is not active against Pseudomonas aeruginosa or Acinetobacter spp.

This short, introductory animated video by Ryan Sheehy describes penicillinase resistant penicillins - Penicillinase resistant penicillins YouTube video.

Carbapenems

Ertapenem, and the antipseudomonals doripenem, imipenem and meropenem are in this subgroup of β-lactams, and their use is generally reserved for known or suspected multidrug-resistant (MDR) bacterial infections. increasing rates of resistance to carbapenems is a clinical problem, as there are limited options that are effective against carbapenem-resistant bacteria (e.g. Klebsiella pneumoniae and other carbapenem-resistant Enterobacteriaceae).

 

Antipseudomonal penicillins

Piperacillin (a ureidopenicillin) is only available in a fixed-dose combination with the β-lactamase inhibitor tazobactam.

Ticarcillin (a carboxypenicillin) is only available in a fixed-dose combination with β-lactamase inhibiting clavulanic acid.

Both of these preparations are broad spectrum antibiotics that are effective against a range of Gram +ve , Gram -ve bacteria, and anaerobic bacteria. Piperacillin + tazobactam is active against a wider range of Gram -ve organisms than ticarcillin + clavulanic acid and it is more active against Pseudomonas aeruginosa. Neither of these antibacterials combat MRSA. They are typically used to treat septicaemia, hospital-acquired pneumonia, and complicated infections involving the urinary tract, skin and soft tissues, or intra-abdomen. Co-administration of an aminoglycoside (e.g. gentamicin) with these antipseudomonal penicillin preparations effectively combats severe pseudomonas infections.

This short video (3:22) is part of an introductory series of videos on antibiotic classes produced by Ryan Sheehy of Kansas City University. It uses a narrated animation to introduce you to the basic structure, mechanisms of action and adverse effects of penicillin G (benzylpenicillin). Penicillin G is the original penicillin that was discovered in 1928 and first used in humans in the 1940s. It is active against a wide range of microorganisms, however its use is hindered by susceptibility to β-lactamases. Penicillin G has greatest activity against Gram-positive bacteria (e.g. Streptococcus pneumoniae, Streptococcus pyogenes), some Gram-negative cocci (e.g. Neisseria meningitidis, Neisseria gonorrhoeae) and non-β-lactamase producing anaerobes. Adverse effects include hypersensitivity (penicillin allergy) and gastrointestinal disturbances.

No votes yet

β-lactam antibiotics are so-called because they all contain a β-lactam ring in their chemical structures. In general these antibiotics act to inhibit bacterial wall synthesis. They are broad-spectrum antibiotics with activity against both Gram +ve and Gram -ve bacterial strains.

Subgroups include: penicillin derivatives (penams) and carbapenems which are discussed in more detail below, cephalosporins (cephems), monobactams, and carbacephems (which are reviewed more extensively in other topics within this Drugs for Infections module.

Bacteria can produce β-lactamase as a mechanism of acquired resistance to β-lactam antibiotics. Co-administration of β-lactamase inhibitors can partially mitigate resistance. This short introductory animated video by Ryan Sheehy describes β-lactamase inhibitors in more detail-  Betalactamse inhibitors YouTube video

β-lactamase-sensitive penicillins

Ampicillin is inactivated by penicillinases. Since the majority of staphylococci and E. coli strains and some Haemophilus influenzae strains are now resistant to ampicillin, it should not be used in the hospital setting or without first considering the likelihood of resistance. The main indications for ampicillin treatment are exacerbations of chronic bronchitis and middle ear infections due to Streptococcus pneumoniae and H. influenzae, and for urinary-tract infections.

A fixed-dose combination of ampicillin plus flucloxacillin (co-fluampicil) is available to treat streptococci or staphylococci infections such as cellulitis.

Amoxicillin, a derivative of ampicillin with improved oral absorption, has a similar antibacterial spectrum. It is notably used for the treatment of Lyme disease.

Co-amoxiclav (amoxicillin + clavulanic acid) is active against β-lactamase-producing bacteria that are resistant to amoxicillin, such as resistant strains of Staph. aureus, E. coli, and H. influenzae, as well as many Bacteroides and Klebsiella spp. Its use should be restricted to the treatment of infections likely, or known, to be caused by amoxicillin-resistant β-lactamase producing bacterial strains.

Benzylpenicillin (Penicillin G) is inactivated by gastric acid so has to be delivered by injection. It is effective against many streptococcal (including pneumococcal), gonococcal, and meningococcal infections, anthrax, diphtheria, gas-gangrene, and leptospirosis. Some pneumococci, meningococci, and gonococci strains are less sensitive to benzylpenicillin. Although benzylpenicillin is active against tetanus, treatment with metronidazole is the preferred option. Benzathine benzylpenicillin is given by intramuscular injection to treat early syphilis and late latent syphilis.

Phenoxymethylpenicillin (Penicillin V) is similarly active to benzylpenicillin but is acid-resistant, so can be delivered orally. The principal indications for its use are respiratory-tract infections in children, streptococcal tonsillitis, and for continuing benzylpenicillin-initiated treatment when clinical response has begun. Phenoxymethylpenicillin should not be used for meningococcal or gonococcal infections.

Penicillinase- and β-lactamase-resistant penicillins

Flucloxacillin is not inactivated by penicillinases so it is effective against infections caused by penicillin-resistant staphylococci, and this is its principal use. It is acid-resistant and orally active.

Temocillin is stable against a wide range of β-lactamases. Its use should be reserved for the treatment of infections caused by β-lactamase-producing strains of Gram -ve bacteria, including those that are resistant to third-generation cephalosporins. Temocillin is not active against Pseudomonas aeruginosa or Acinetobacter spp.

This short, introductory animated video by Ryan Sheehy describes penicillinase resistant penicillins - Penicillinase resistant penicillins YouTube video.

Carbapenems

Ertapenem, and the antipseudomonals doripenem, imipenem and meropenem are in this subgroup of β-lactams, and their use is generally reserved for known or suspected multidrug-resistant (MDR) bacterial infections. increasing rates of resistance to carbapenems is a clinical problem, as there are limited options that are effective against carbapenem-resistant bacteria (e.g. Klebsiella pneumoniae and other carbapenem-resistant Enterobacteriaceae).

 

Antipseudomonal penicillins

Piperacillin (a ureidopenicillin) is only available in a fixed-dose combination with the β-lactamase inhibitor tazobactam.

Ticarcillin (a carboxypenicillin) is only available in a fixed-dose combination with β-lactamase inhibiting clavulanic acid.

Both of these preparations are broad spectrum antibiotics that are effective against a range of Gram +ve , Gram -ve bacteria, and anaerobic bacteria. Piperacillin + tazobactam is active against a wider range of Gram -ve organisms than ticarcillin + clavulanic acid and it is more active against Pseudomonas aeruginosa. Neither of these antibacterials combat MRSA. They are typically used to treat septicaemia, hospital-acquired pneumonia, and complicated infections involving the urinary tract, skin and soft tissues, or intra-abdomen. Co-administration of an aminoglycoside (e.g. gentamicin) with these antipseudomonal penicillin preparations effectively combats severe pseudomonas infections.

This is a short (3:09) animated video that describes antipseudomonal penicillins that was produced by Ryan Sheehy. It is suitable for beginners. Structurally this group consists of carboxypenicillins and ureidopenicillins. Piperacillin is a clinically used ureidopenicillin. Antipseudomonal penicillins have extended Gram negative coverage compared to other penicillins, and are generally used to treat Pseudomonas aeruginosa infections.

No votes yet

β-lactam antibiotics are so-called because they all contain a β-lactam ring in their chemical structures. In general these antibiotics act to inhibit bacterial wall synthesis. They are broad-spectrum antibiotics with activity against both Gram +ve and Gram -ve bacterial strains.

Subgroups include: penicillin derivatives (penams) and carbapenems which are discussed in more detail below, cephalosporins (cephems), monobactams, and carbacephems (which are reviewed more extensively in other topics within this Drugs for Infections module.

Bacteria can produce β-lactamase as a mechanism of acquired resistance to β-lactam antibiotics. Co-administration of β-lactamase inhibitors can partially mitigate resistance. This short introductory animated video by Ryan Sheehy describes β-lactamase inhibitors in more detail-  Betalactamse inhibitors YouTube video

β-lactamase-sensitive penicillins

Ampicillin is inactivated by penicillinases. Since the majority of staphylococci and E. coli strains and some Haemophilus influenzae strains are now resistant to ampicillin, it should not be used in the hospital setting or without first considering the likelihood of resistance. The main indications for ampicillin treatment are exacerbations of chronic bronchitis and middle ear infections due to Streptococcus pneumoniae and H. influenzae, and for urinary-tract infections.

A fixed-dose combination of ampicillin plus flucloxacillin (co-fluampicil) is available to treat streptococci or staphylococci infections such as cellulitis.

Amoxicillin, a derivative of ampicillin with improved oral absorption, has a similar antibacterial spectrum. It is notably used for the treatment of Lyme disease.

Co-amoxiclav (amoxicillin + clavulanic acid) is active against β-lactamase-producing bacteria that are resistant to amoxicillin, such as resistant strains of Staph. aureus, E. coli, and H. influenzae, as well as many Bacteroides and Klebsiella spp. Its use should be restricted to the treatment of infections likely, or known, to be caused by amoxicillin-resistant β-lactamase producing bacterial strains.

Benzylpenicillin (Penicillin G) is inactivated by gastric acid so has to be delivered by injection. It is effective against many streptococcal (including pneumococcal), gonococcal, and meningococcal infections, anthrax, diphtheria, gas-gangrene, and leptospirosis. Some pneumococci, meningococci, and gonococci strains are less sensitive to benzylpenicillin. Although benzylpenicillin is active against tetanus, treatment with metronidazole is the preferred option. Benzathine benzylpenicillin is given by intramuscular injection to treat early syphilis and late latent syphilis.

Phenoxymethylpenicillin (Penicillin V) is similarly active to benzylpenicillin but is acid-resistant, so can be delivered orally. The principal indications for its use are respiratory-tract infections in children, streptococcal tonsillitis, and for continuing benzylpenicillin-initiated treatment when clinical response has begun. Phenoxymethylpenicillin should not be used for meningococcal or gonococcal infections.

Penicillinase- and β-lactamase-resistant penicillins

Flucloxacillin is not inactivated by penicillinases so it is effective against infections caused by penicillin-resistant staphylococci, and this is its principal use. It is acid-resistant and orally active.

Temocillin is stable against a wide range of β-lactamases. Its use should be reserved for the treatment of infections caused by β-lactamase-producing strains of Gram -ve bacteria, including those that are resistant to third-generation cephalosporins. Temocillin is not active against Pseudomonas aeruginosa or Acinetobacter spp.

This short, introductory animated video by Ryan Sheehy describes penicillinase resistant penicillins - Penicillinase resistant penicillins YouTube video.

Carbapenems

Ertapenem, and the antipseudomonals doripenem, imipenem and meropenem are in this subgroup of β-lactams, and their use is generally reserved for known or suspected multidrug-resistant (MDR) bacterial infections. increasing rates of resistance to carbapenems is a clinical problem, as there are limited options that are effective against carbapenem-resistant bacteria (e.g. Klebsiella pneumoniae and other carbapenem-resistant Enterobacteriaceae).

 

Antipseudomonal penicillins

Piperacillin (a ureidopenicillin) is only available in a fixed-dose combination with the β-lactamase inhibitor tazobactam.

Ticarcillin (a carboxypenicillin) is only available in a fixed-dose combination with β-lactamase inhibiting clavulanic acid.

Both of these preparations are broad spectrum antibiotics that are effective against a range of Gram +ve , Gram -ve bacteria, and anaerobic bacteria. Piperacillin + tazobactam is active against a wider range of Gram -ve organisms than ticarcillin + clavulanic acid and it is more active against Pseudomonas aeruginosa. Neither of these antibacterials combat MRSA. They are typically used to treat septicaemia, hospital-acquired pneumonia, and complicated infections involving the urinary tract, skin and soft tissues, or intra-abdomen. Co-administration of an aminoglycoside (e.g. gentamicin) with these antipseudomonal penicillin preparations effectively combats severe pseudomonas infections.

This is a short (5:05) animated video that was produced by Ryan Sheehy describes carbapenem antibiotics in more detail. It is suitable for beginners.

No votes yet

Polymyxin antibiotics

Polymyxin antibiotics are naturally derived molecules, and are bacterial nonribosomal peptides. Mechanistically, they interact with phospholipids in the bacterial membrane, and disrupt membrane integrity. In addition, polymixins bind to endotoxin to reduce the destructive biological effects of endotoxin in the host. Their mechanism of action means that polymixins are active strictly against Gram negative bacteria. Susceptible organisms include aerobes such as enterobacteriaceae, Pseudomonas spp.,and Acinetobacter spp.

There are two clinically used polymixins: polymixin B (a mixture of B1 and B2) and colistin (polymixin E), which were originally isolated from the Gram-positive bacteria Bacillus polymyxa and Bacillus colistinus respectively. Colistin is administered topically whereas its methylate derivative is used for intravenous infusion. Polymyxin antibiotics are relatively neurotoxic and nephrotoxic, so are principally used to treat serious infections caused by highly antibiotic resistant bacteria.

 

 

 

This short video (4:14) is part of an introductory series of videos on antibiotic classes produced by Ryan Sheehy of Kansas City University. It uses a narrated animation to introduce you to the basic structure and mechanisms of action of polymyxin antibiotics, which are active strictly against Gram negative bacteria. Susceptible organisms include aerobes such as enterobacteriaceae, Pseudomonas spp.,and Acinetobacter spp. Polymyxin antibiotics are relatively neurotoxic and nephrotoxic, so are principally used to treat serious infections caused by highly resistant bacteria.

No votes yet

Quinolones

Bacteria replicate DNA via a unique enzyme called DNA gyrase (or topoisomerase II). DNA at the replication fork exist in a positively-supercoiled arrangement and the structure is strained. DNA gyrase nicks one strand of the DNA (say at a supercoiled segment behind) and reseals the strand after it un-coils at the front. This process restores the usual, negatively-supercoiled and stabilised, unstrained state. Another enzyme, topoisomerase IV, acts to untangle the newly replicated DNA. Both topoisomerases II & IV can be inhibited by fluoroquinolones, but activity against topoisomerase II is more clinically relevant at present.

Ciprofloxacin is a representative example of fluoroquinolones, so named because compounds in the class possess a fluorine. Fluoroquinolones inhibit the activity of DNA gyrase, thus stopping DNA replication. Drugs in this class should be avoided in pregnant women (concerning fetus) and those under age 18 as the developing bones and cartilage will be affected. Unwanted effects are infrequent and mild, but ciprofloxacin is a known cytochrome P450 inhibitor. Thus, interactions with other P450 inhibitors such as theophylline can produce CNS effects such as headache, dizziness and convulsions.

Fluoroquinolones have a broad spectrum of antibacterial activity, but usage is best reserved for Gram-negative (Gm-) bacteria, including against Acinetobacter baumannii & Pseudomonas aeruginosa (combined with aminoglycoside), Haemophilus influenzae, enterobacteria (Enterobacter, E. coli, K. pneumoniae). Resistance to fluoroquinolones may arise most commonly when the structure of DNA gyrase is altered. This may result in weaker drug-binding or a binding site that is shielded from the drug. It should also be noted that inactivation by acetylation occurs via an enzyme that does the same to aminoglycosides.

Links to PubChem entries: ciprofloxacin (a second-generation fluoroquinolone); levoflaxacin (a third-generation fluoroquinolone); moxifloxacin (a fourth-generation fluoroquinolone). These entries list the key physico-chemical and pharmacological properties of these fluoroquinolone drugs. Synopses of individual reports on adverse drug reactions are included, as are examples of various drug formulations on the market.

Dr Willmann Liang

Part of this narrated video (from 3:08 to 4:43) gives an overview of the mechanisms of action of fluoroquinolones.  Mechanisms of drug resistance are also briefly introduced.

Intermediate level.

Author: MedLecturesMadeEasy

No votes yet

Bacteria replicate DNA via a unique enzyme called DNA gyrase (or topoisomerase II). DNA at the replication fork exist in a positively-supercoiled arrangement and the structure is strained. DNA gyrase nicks one strand of the DNA (say at a supercoiled segment behind) and reseals the strand after it un-coils at the front. This process restores the usual, negatively-supercoiled and stabilised, unstrained state. Another enzyme, topoisomerase IV, acts to untangle the newly replicated DNA. Both topoisomerases II & IV can be inhibited by fluoroquinolones, but activity against topoisomerase II is more clinically relevant at present.

Ciprofloxacin is a representative example of fluoroquinolones, so named because compounds in the class possess a fluorine. Fluoroquinolones inhibit the activity of DNA gyrase, thus stopping DNA replication. Drugs in this class should be avoided in pregnant women (concerning fetus) and those under age 18 as the developing bones and cartilage will be affected. Unwanted effects are infrequent and mild, but ciprofloxacin is a known cytochrome P450 inhibitor. Thus, interactions with other P450 inhibitors such as theophylline can produce CNS effects such as headache, dizziness and convulsions.

Fluoroquinolones have a broad spectrum of antibacterial activity, but usage is best reserved for Gram-negative (Gm-) bacteria, including against Acinetobacter baumannii & Pseudomonas aeruginosa (combined with aminoglycoside), Haemophilus influenzae, enterobacteria (Enterobacter, E. coli, K. pneumoniae). Resistance to fluoroquinolones may arise most commonly when the structure of DNA gyrase is altered. This may result in weaker drug-binding or a binding site that is shielded from the drug. It should also be noted that inactivation by acetylation occurs via an enzyme that does the same to aminoglycosides.

Links to PubChem entries: ciprofloxacin (a second-generation fluoroquinolone); levoflaxacin (a third-generation fluoroquinolone); moxifloxacin (a fourth-generation fluoroquinolone). These entries list the key physico-chemical and pharmacological properties of these fluoroquinolone drugs. Synopses of individual reports on adverse drug reactions are included, as are examples of various drug formulations on the market.

Dr Willmann Liang

This is a 7-minute animation showing the mechanism of action of the fluoroquinolones. Students will gain the most from this animation if they have an understanding of DNA replication.  A brief introduction of this process is also given in the first part of this video.  From 5:32 onward, mechanisms of resistance to fluoroquinolones are described, with reference to altered drug targets.  This video would be useful together with other resources related to the comprehensive pharmacology of the quinolones.

Advanced level

Author: Mechanisms in Medicine

No votes yet

Bacteria replicate DNA via a unique enzyme called DNA gyrase (or topoisomerase II). DNA at the replication fork exist in a positively-supercoiled arrangement and the structure is strained. DNA gyrase nicks one strand of the DNA (say at a supercoiled segment behind) and reseals the strand after it un-coils at the front. This process restores the usual, negatively-supercoiled and stabilised, unstrained state. Another enzyme, topoisomerase IV, acts to untangle the newly replicated DNA. Both topoisomerases II & IV can be inhibited by fluoroquinolones, but activity against topoisomerase II is more clinically relevant at present.

Ciprofloxacin is a representative example of fluoroquinolones, so named because compounds in the class possess a fluorine. Fluoroquinolones inhibit the activity of DNA gyrase, thus stopping DNA replication. Drugs in this class should be avoided in pregnant women (concerning fetus) and those under age 18 as the developing bones and cartilage will be affected. Unwanted effects are infrequent and mild, but ciprofloxacin is a known cytochrome P450 inhibitor. Thus, interactions with other P450 inhibitors such as theophylline can produce CNS effects such as headache, dizziness and convulsions.

Fluoroquinolones have a broad spectrum of antibacterial activity, but usage is best reserved for Gram-negative (Gm-) bacteria, including against Acinetobacter baumannii & Pseudomonas aeruginosa (combined with aminoglycoside), Haemophilus influenzae, enterobacteria (Enterobacter, E. coli, K. pneumoniae). Resistance to fluoroquinolones may arise most commonly when the structure of DNA gyrase is altered. This may result in weaker drug-binding or a binding site that is shielded from the drug. It should also be noted that inactivation by acetylation occurs via an enzyme that does the same to aminoglycosides.

Links to PubChem entries: ciprofloxacin (a second-generation fluoroquinolone); levoflaxacin (a third-generation fluoroquinolone); moxifloxacin (a fourth-generation fluoroquinolone). These entries list the key physico-chemical and pharmacological properties of these fluoroquinolone drugs. Synopses of individual reports on adverse drug reactions are included, as are examples of various drug formulations on the market.

Dr Willmann Liang

This article provides an overview of the general pharmacology of fluoroquinolones.  Important unwanted effects are also described in detail.  A note is included about restricted fluoroquinolone use in the USA due to the adverse drug effects.

Advanced level

Author: David C Hooper

Note that Institutional subscription may be required to access UpToDate.com articles.

No votes yet

Bacteria replicate DNA via a unique enzyme called DNA gyrase (or topoisomerase II). DNA at the replication fork exist in a positively-supercoiled arrangement and the structure is strained. DNA gyrase nicks one strand of the DNA (say at a supercoiled segment behind) and reseals the strand after it un-coils at the front. This process restores the usual, negatively-supercoiled and stabilised, unstrained state. Another enzyme, topoisomerase IV, acts to untangle the newly replicated DNA. Both topoisomerases II & IV can be inhibited by fluoroquinolones, but activity against topoisomerase II is more clinically relevant at present.

Ciprofloxacin is a representative example of fluoroquinolones, so named because compounds in the class possess a fluorine. Fluoroquinolones inhibit the activity of DNA gyrase, thus stopping DNA replication. Drugs in this class should be avoided in pregnant women (concerning fetus) and those under age 18 as the developing bones and cartilage will be affected. Unwanted effects are infrequent and mild, but ciprofloxacin is a known cytochrome P450 inhibitor. Thus, interactions with other P450 inhibitors such as theophylline can produce CNS effects such as headache, dizziness and convulsions.

Fluoroquinolones have a broad spectrum of antibacterial activity, but usage is best reserved for Gram-negative (Gm-) bacteria, including against Acinetobacter baumannii & Pseudomonas aeruginosa (combined with aminoglycoside), Haemophilus influenzae, enterobacteria (Enterobacter, E. coli, K. pneumoniae). Resistance to fluoroquinolones may arise most commonly when the structure of DNA gyrase is altered. This may result in weaker drug-binding or a binding site that is shielded from the drug. It should also be noted that inactivation by acetylation occurs via an enzyme that does the same to aminoglycosides.

Links to PubChem entries: ciprofloxacin (a second-generation fluoroquinolone); levoflaxacin (a third-generation fluoroquinolone); moxifloxacin (a fourth-generation fluoroquinolone). These entries list the key physico-chemical and pharmacological properties of these fluoroquinolone drugs. Synopses of individual reports on adverse drug reactions are included, as are examples of various drug formulations on the market.

Dr Willmann Liang

Part of this narrated video (from 19:34 to 22:08) introduces examples of different generations of fluoroquinolones. Their spectra of antibacterial activity are compared.

Author: Eric Strong

Advanced level 

No votes yet

Bacteria replicate DNA via a unique enzyme called DNA gyrase (or topoisomerase II). DNA at the replication fork exist in a positively-supercoiled arrangement and the structure is strained. DNA gyrase nicks one strand of the DNA (say at a supercoiled segment behind) and reseals the strand after it un-coils at the front. This process restores the usual, negatively-supercoiled and stabilised, unstrained state. Another enzyme, topoisomerase IV, acts to untangle the newly replicated DNA. Both topoisomerases II & IV can be inhibited by fluoroquinolones, but activity against topoisomerase II is more clinically relevant at present.

Ciprofloxacin is a representative example of fluoroquinolones, so named because compounds in the class possess a fluorine. Fluoroquinolones inhibit the activity of DNA gyrase, thus stopping DNA replication. Drugs in this class should be avoided in pregnant women (concerning fetus) and those under age 18 as the developing bones and cartilage will be affected. Unwanted effects are infrequent and mild, but ciprofloxacin is a known cytochrome P450 inhibitor. Thus, interactions with other P450 inhibitors such as theophylline can produce CNS effects such as headache, dizziness and convulsions.

Fluoroquinolones have a broad spectrum of antibacterial activity, but usage is best reserved for Gram-negative (Gm-) bacteria, including against Acinetobacter baumannii & Pseudomonas aeruginosa (combined with aminoglycoside), Haemophilus influenzae, enterobacteria (Enterobacter, E. coli, K. pneumoniae). Resistance to fluoroquinolones may arise most commonly when the structure of DNA gyrase is altered. This may result in weaker drug-binding or a binding site that is shielded from the drug. It should also be noted that inactivation by acetylation occurs via an enzyme that does the same to aminoglycosides.

Links to PubChem entries: ciprofloxacin (a second-generation fluoroquinolone); levoflaxacin (a third-generation fluoroquinolone); moxifloxacin (a fourth-generation fluoroquinolone). These entries list the key physico-chemical and pharmacological properties of these fluoroquinolone drugs. Synopses of individual reports on adverse drug reactions are included, as are examples of various drug formulations on the market.

Dr Willmann Liang

This short video (6:55) is part of an introductory series of videos on antibiotic classes produced by Ryan Sheehy of Kansas City University. It uses a narrated animation to introduce you to the basic structure, mechanisms of action and clinical uses of fluoroquinolones. Commonly used drugs in this class include ciprofloxacin, levofloxacin, moxifloxacin, norfloxacin, and ofloxacin. The fluoroquinolones are a family of broad spectrum, systemic antibacterial agents that have been used widely as therapy of respiratory and urinary tract infections. Fluoroquinolones are active against a wide range of aerobic gram-positive (Staphylococci, Streptococcus pneumoniae and viridans, Enterococcus faecalis, Listeria monocytogenes, and Nocardia) and gram-negative organisms (Neisseria meningitides and gonorrhoeae, Haemophilus influenzae, and most clinically important Enterobacteriaceae species). The fluoroquinolones probably act by inhibition of type II DNA toposiomerases (gyrases) that are required for synthesis of bacterial mRNAs (transcription) and DNA replication.

No votes yet

Sulphonamides & trimethoprim (CO-trimoxazole)

Bacteria must generate their own precursors to nucleic acids. Para-aminobenzoic acid (PABA), together with a pteridine derivative and glutamic acid are needed to synthesise these precursors. The first step is catalysed by dihydropteroate synthetase (DHPS) to generate dihydropteric acid. A second enzyme, dihydrofolate synthetase (DHFS), adds glutamic acid and produces dihydrofolic acid. The last step, via dihydrofolate reductase (DHFR), yields tetrahydrofolic acid (THF). THF is then utilised in other pathways to generate nucleic acids. Notable unwanted effects of sulphonamides include photosensitivity, topical hypersensitivity and in severe cases, Stevens-Johnson syndrome and toxic epidermal necrolysis.

Sulfonamides are compounds that possess a structure similar to PABA. These PABA analogues compete with the authentic PABA for DHPS, thus suppressing dihydropteroic acid production, and subsequently less THF is produced. Humans can obtain THF from diet, so blocking DHPS only affects bacteria. In fact, humans do not have DHPS. Trimethoprim is a pteridine analogue that blocks the activity of DHFR. Humans have DHFR, but trimethoprim is much more potent to bacterial DHFR. Trimethoprim is often given together with a sulphonamide (commonly sulfomethoxazole). The combined formulation is called co-trimoxazol. Co-trimoxazole interferes with THF synthesis at two points, i.e. concomittant inhibition of both DHPS and DHFR. The combined form serves to potentiate drug effect. Drug resistance is also less likely to be a problem as the susceptible bacteria are under attack at two points of the same biochemical pathway.

Long-term use of co-trimoxazole may bring about the expected unwanted effect of folate deficiency if dietary intake is below normal. Co-trimoxazole has a broad spectrum of antibacterial activity, but enterococci and P. aeruginosa are intrinsically resistant.

Co-trimoxazole can be used against methicillin-resistant Staphylococcus aureus (MRSA) together with drainage, as well as against extended-spectrum beta-lactamase-producing (ESBL+) E. coli and Klebsiella pneumoniae infections in the urinary tract. Resistance to co-trimoxazole may come in several forms. More commonly, bacteria may possess the ability to produce large amounts of PABA or DHFR, thereby the drugs are rendered useless. Another common mechanism is mutations causing alterations in the drug-binding site(s) of DHPS or DHFR and decreased drug affinity.

Dr Willmann Liang

Key physico-chemical and pharmacological properties of co-trimoxazole are listed under this PubChem entry. Synopses of individual reports on adverse drug reactions are included. Examples of various co-trimoxazole formulations on the market are also provided.

 

No votes yet

Bacteria must generate their own precursors to nucleic acids. Para-aminobenzoic acid (PABA), together with a pteridine derivative and glutamic acid are needed to synthesise these precursors. The first step is catalysed by dihydropteroate synthetase (DHPS) to generate dihydropteric acid. A second enzyme, dihydrofolate synthetase (DHFS), adds glutamic acid and produces dihydrofolic acid. The last step, via dihydrofolate reductase (DHFR), yields tetrahydrofolic acid (THF). THF is then utilised in other pathways to generate nucleic acids. Notable unwanted effects of sulphonamides include photosensitivity, topical hypersensitivity and in severe cases, Stevens-Johnson syndrome and toxic epidermal necrolysis.

Sulfonamides are compounds that possess a structure similar to PABA. These PABA analogues compete with the authentic PABA for DHPS, thus suppressing dihydropteroic acid production, and subsequently less THF is produced. Humans can obtain THF from diet, so blocking DHPS only affects bacteria. In fact, humans do not have DHPS. Trimethoprim is a pteridine analogue that blocks the activity of DHFR. Humans have DHFR, but trimethoprim is much more potent to bacterial DHFR. Trimethoprim is often given together with a sulphonamide (commonly sulfomethoxazole). The combined formulation is called co-trimoxazol. Co-trimoxazole interferes with THF synthesis at two points, i.e. concomittant inhibition of both DHPS and DHFR. The combined form serves to potentiate drug effect. Drug resistance is also less likely to be a problem as the susceptible bacteria are under attack at two points of the same biochemical pathway.

Long-term use of co-trimoxazole may bring about the expected unwanted effect of folate deficiency if dietary intake is below normal. Co-trimoxazole has a broad spectrum of antibacterial activity, but enterococci and P. aeruginosa are intrinsically resistant.

Co-trimoxazole can be used against methicillin-resistant Staphylococcus aureus (MRSA) together with drainage, as well as against extended-spectrum beta-lactamase-producing (ESBL+) E. coli and Klebsiella pneumoniae infections in the urinary tract. Resistance to co-trimoxazole may come in several forms. More commonly, bacteria may possess the ability to produce large amounts of PABA or DHFR, thereby the drugs are rendered useless. Another common mechanism is mutations causing alterations in the drug-binding site(s) of DHPS or DHFR and decreased drug affinity.

Dr Willmann Liang

This article provides specific information on how and where resistance to co-trimoxazole may arise.  Common unwanted effects are also described in greater detail.

Advanced level.

Author: D Byron May

Note that Institutional subscription may be required to access UpToDate.com articles.

No votes yet

Bacteria must generate their own precursors to nucleic acids. Para-aminobenzoic acid (PABA), together with a pteridine derivative and glutamic acid are needed to synthesise these precursors. The first step is catalysed by dihydropteroate synthetase (DHPS) to generate dihydropteric acid. A second enzyme, dihydrofolate synthetase (DHFS), adds glutamic acid and produces dihydrofolic acid. The last step, via dihydrofolate reductase (DHFR), yields tetrahydrofolic acid (THF). THF is then utilised in other pathways to generate nucleic acids. Notable unwanted effects of sulphonamides include photosensitivity, topical hypersensitivity and in severe cases, Stevens-Johnson syndrome and toxic epidermal necrolysis.

Sulfonamides are compounds that possess a structure similar to PABA. These PABA analogues compete with the authentic PABA for DHPS, thus suppressing dihydropteroic acid production, and subsequently less THF is produced. Humans can obtain THF from diet, so blocking DHPS only affects bacteria. In fact, humans do not have DHPS. Trimethoprim is a pteridine analogue that blocks the activity of DHFR. Humans have DHFR, but trimethoprim is much more potent to bacterial DHFR. Trimethoprim is often given together with a sulphonamide (commonly sulfomethoxazole). The combined formulation is called co-trimoxazol. Co-trimoxazole interferes with THF synthesis at two points, i.e. concomittant inhibition of both DHPS and DHFR. The combined form serves to potentiate drug effect. Drug resistance is also less likely to be a problem as the susceptible bacteria are under attack at two points of the same biochemical pathway.

Long-term use of co-trimoxazole may bring about the expected unwanted effect of folate deficiency if dietary intake is below normal. Co-trimoxazole has a broad spectrum of antibacterial activity, but enterococci and P. aeruginosa are intrinsically resistant.

Co-trimoxazole can be used against methicillin-resistant Staphylococcus aureus (MRSA) together with drainage, as well as against extended-spectrum beta-lactamase-producing (ESBL+) E. coli and Klebsiella pneumoniae infections in the urinary tract. Resistance to co-trimoxazole may come in several forms. More commonly, bacteria may possess the ability to produce large amounts of PABA or DHFR, thereby the drugs are rendered useless. Another common mechanism is mutations causing alterations in the drug-binding site(s) of DHPS or DHFR and decreased drug affinity.

Dr Willmann Liang

This short video (8:51) is part of an introductory series of videos on antibiotic classes produced by Ryan Sheehy of Kansas City University. It uses a narrated animation to introduce you to the basic structure and mechanisms of action of sulfonamide and benzylpyrimidine class antibiotics. The video concentrates on sulfamethoxazole and trimethoprin as examples of each class. It is suitable for beginners.

No votes yet

Bacteria must generate their own precursors to nucleic acids. Para-aminobenzoic acid (PABA), together with a pteridine derivative and glutamic acid are needed to synthesise these precursors. The first step is catalysed by dihydropteroate synthetase (DHPS) to generate dihydropteric acid. A second enzyme, dihydrofolate synthetase (DHFS), adds glutamic acid and produces dihydrofolic acid. The last step, via dihydrofolate reductase (DHFR), yields tetrahydrofolic acid (THF). THF is then utilised in other pathways to generate nucleic acids. Notable unwanted effects of sulphonamides include photosensitivity, topical hypersensitivity and in severe cases, Stevens-Johnson syndrome and toxic epidermal necrolysis.

Sulfonamides are compounds that possess a structure similar to PABA. These PABA analogues compete with the authentic PABA for DHPS, thus suppressing dihydropteroic acid production, and subsequently less THF is produced. Humans can obtain THF from diet, so blocking DHPS only affects bacteria. In fact, humans do not have DHPS. Trimethoprim is a pteridine analogue that blocks the activity of DHFR. Humans have DHFR, but trimethoprim is much more potent to bacterial DHFR. Trimethoprim is often given together with a sulphonamide (commonly sulfomethoxazole). The combined formulation is called co-trimoxazol. Co-trimoxazole interferes with THF synthesis at two points, i.e. concomittant inhibition of both DHPS and DHFR. The combined form serves to potentiate drug effect. Drug resistance is also less likely to be a problem as the susceptible bacteria are under attack at two points of the same biochemical pathway.

Long-term use of co-trimoxazole may bring about the expected unwanted effect of folate deficiency if dietary intake is below normal. Co-trimoxazole has a broad spectrum of antibacterial activity, but enterococci and P. aeruginosa are intrinsically resistant.

Co-trimoxazole can be used against methicillin-resistant Staphylococcus aureus (MRSA) together with drainage, as well as against extended-spectrum beta-lactamase-producing (ESBL+) E. coli and Klebsiella pneumoniae infections in the urinary tract. Resistance to co-trimoxazole may come in several forms. More commonly, bacteria may possess the ability to produce large amounts of PABA or DHFR, thereby the drugs are rendered useless. Another common mechanism is mutations causing alterations in the drug-binding site(s) of DHPS or DHFR and decreased drug affinity.

Dr Willmann Liang

This un-narrated clay animation highlights the inhibitory effects of co-trimoxazole on DHPS and DHFR, thus preventing the conversion of PABA to dihydrofolic acid and tetrahydrofolic acid. Suitable for beginners.

Author: Joshua Shafer

No votes yet

Bacteria must generate their own precursors to nucleic acids. Para-aminobenzoic acid (PABA), together with a pteridine derivative and glutamic acid are needed to synthesise these precursors. The first step is catalysed by dihydropteroate synthetase (DHPS) to generate dihydropteric acid. A second enzyme, dihydrofolate synthetase (DHFS), adds glutamic acid and produces dihydrofolic acid. The last step, via dihydrofolate reductase (DHFR), yields tetrahydrofolic acid (THF). THF is then utilised in other pathways to generate nucleic acids. Notable unwanted effects of sulphonamides include photosensitivity, topical hypersensitivity and in severe cases, Stevens-Johnson syndrome and toxic epidermal necrolysis.

Sulfonamides are compounds that possess a structure similar to PABA. These PABA analogues compete with the authentic PABA for DHPS, thus suppressing dihydropteroic acid production, and subsequently less THF is produced. Humans can obtain THF from diet, so blocking DHPS only affects bacteria. In fact, humans do not have DHPS. Trimethoprim is a pteridine analogue that blocks the activity of DHFR. Humans have DHFR, but trimethoprim is much more potent to bacterial DHFR. Trimethoprim is often given together with a sulphonamide (commonly sulfomethoxazole). The combined formulation is called co-trimoxazol. Co-trimoxazole interferes with THF synthesis at two points, i.e. concomittant inhibition of both DHPS and DHFR. The combined form serves to potentiate drug effect. Drug resistance is also less likely to be a problem as the susceptible bacteria are under attack at two points of the same biochemical pathway.

Long-term use of co-trimoxazole may bring about the expected unwanted effect of folate deficiency if dietary intake is below normal. Co-trimoxazole has a broad spectrum of antibacterial activity, but enterococci and P. aeruginosa are intrinsically resistant.

Co-trimoxazole can be used against methicillin-resistant Staphylococcus aureus (MRSA) together with drainage, as well as against extended-spectrum beta-lactamase-producing (ESBL+) E. coli and Klebsiella pneumoniae infections in the urinary tract. Resistance to co-trimoxazole may come in several forms. More commonly, bacteria may possess the ability to produce large amounts of PABA or DHFR, thereby the drugs are rendered useless. Another common mechanism is mutations causing alterations in the drug-binding site(s) of DHPS or DHFR and decreased drug affinity.

Dr Willmann Liang

The first part of this video (up to 3:08) gives a more detailed overview of bacterial nucleic acid synthesis, and how this process is inhibited by co-trimoxazole.  Mechanisms of drug resistance are also briefly introduced.

Intermediate level.

Author: MedLecturesMadeEasy

No votes yet

Tetracyclines and glycycylines

Tetracyclines and glycycylines are structurally related antibiotics. They are either isolated directly from certain Streptomyces spp., or can produced semi-synthetically as derivatives of the isolated compounds.

Tetracyclines are named after their tetracyclic nucleus (4 linear fused hydrocarbon rings). Differences between tetracycline class antibiotics are determined by the range of functional groups that are attached to the hydrocarbon rings. They have broad range bacteriostatic antibacterial activity. Mechanistically, the tetracyclines  pass through porin channels in the bacterial membrane, and block protein synthesis by reversibly inhibiting the function of the bacterial 30S ribosomal subunit. 

Numerous tetracyclines are used in clinical practice, principally to treat urinary tract, respiratory tract, intestinal infections, acne and rosacea. Examples include tetracycline, oxytetracycline, doxycycline and minocycline.The tetracyclines can be useful where patients are allergic to β-lactam and macrolide antibiotics. However, tetracycline use has been limited due to widespread development of resistance in previously sensitive bacteria.

Only one glycycyline is in clinical use- tigecycline.

This short video (5:50) is part of an introductory series of videos on antibiotic classes produced by Ryan Sheehy of Kansas City University. It uses a narrated animation to introduce you to the basic structure and mechanisms of action of tetracycline antibiotics, and the single glycylcycline in clinical use, tigecycline. It is suitable for beginners.

No votes yet

Drugs for HIV infections

HIV medications are generally classified according to their mechanistic action.

The main classes are:

  • Nucleoside/Nucleotide Reverse Transcriptase Inhibitors (NRTIs)
  • Non-nucleoside Reverse Transcriptase Inhibitors (NNRTIs)
  • Protease Inhibitors (PIs)
  • Entry (or Fusion) Inhibitors
  • Integrase Inhibitors (or integrase strand transfer inhibitors (INSTIs))
  • Attachment Inhibitors
  • Capsid Inhibitors

 

Nucleoside/Nucleotide Reverse Transcriptase Inhibitors (NRTIs)

NRTIs inhibit activity of reverse transcriptase, a viral DNA polymerase that is required for replication of HIV and other retroviruses. Viral reverse transcriptase copies the single stand of the HIV’s RNA genome creating a double-stranded viral DNA that is able to integrate into the host chromosomal DNA. Host transcription and translation are hijacked to reproduce the virus. This group of drugs are analogues of the host’s endogenous deoxynucleotides that are required to synthesize viral DNA, but when incorporated in to a growing DNA molecule they block further elongation, acting as chain terminators. Drugs of this type can be either nucleoside or nucleotide analogues, with the former requiring kinase-mediated phosphorylation to generate active triphosphate molecules. Nucleoside reverse transcriptase inhibitors were the first type of ART drugs to be developed.

Examples include:

    Abacavir, or ABC (Ziagen)

    Didanosine, or ddl (Videx)

    Emtricitabine, or FTC (Emtriva)

    Lamivudine, or 3TC (Epivir)

    Stavudine, or d4T (Zerit)

    Tenofovir, or TDF (Viread)

    Zidovudine, or AZT or ZDV (Retrovir)

 

Non-nucleoside Reverse Transcriptase Inhibitors (NNRTIs)

NNRTIs bind directly to the viral reverse transcriptase and inhibit its activity. This action prevents viral replication.

    Delavirdine (Rescriptor)

    Efavirenz (Sustiva)

    Etravirine (Intelence)

    Nevirapine (Viramune)

    Rilpivirine (Edurant)

 

Protease Inhibitors (PIs)

HIV protease inhibitors are peptidomimetics that competitively inhibit the action of the virus aspartyl protease, and enzyme crucial for the proteolytic cleavage of nascent polypeptide precursors into mature viral proteins.

    Atazanavir, or ATV (Reyataz)

    Darunavir, or DRV (Prezista)

    Fosamprenavir, or FPV (Lexiva)

    Indinavir, or IDV (Crixivan)

    Lopinavir + ritonavir, or LPV/r (Kaletra)

    Nelfinavir, or NFV (Viracept)

    Ritonavir, or RTV (Norvir)

    Saquinavir, or SQV (Invirase)

    Tipranavir, or TPV (Aptivus)

    Cobicistat (Tybost) is an adjuvant drug that increases atazanavir and darunavir efficacy, but it can cause life-threatening kidney problems if it is adminstered with    certain other medicines.

    Atazanavir + cobicistat, or ATV/COBI (Evotaz)

    Darunavir + cobicistat, or DRV/COBI (Prezcobix)

 

These first three groups of drugs work at the level of the HIV infected cell to inhibit viral replication.

The next groups of drugs have different mechanisms of action.

Entry (or Fusion) Inhibitors

Drugs of this class block viral fusion and entry to the T cells.

Enfuvirtide, or ENF or T-20 (Fuzeon), is a biomimetic peptide that binds to the viral transmembrane protein gp41, and inhibits formation of the entry pore that is required for the capsid of the virus to enter the cell. Enfuvirtide is active against HIV-1, with very low activity against HIV-2. Enfuvirtide is delivered by injection, so adherence may be an issue for some patients.

In March 2018, the US FDA approved a first-in-class treatment for heavily treatment-experienced patients with multidrug resistant HIV. Ibalizumab-uiyk (proprietary name Trogarzo; IMGT link) is an anti-CD4 (CXCR4) monoclonal antibody that inhibits the viral entry process (see Jacobson et al. (2009)), and is able to block CCR5- and CXCR4-tropic viruses. Ibalizumab-uiyk is to be used in combination with an optimized background regimen of other antiretroviral drugs.

 

CCR5 Antagonist

Drugs with this action are also entry inhibitors, but with a distinct mechanism of action compared to enfuvirtide. The CCR5 chemokine receptor is an important co-receptor that HIV-1 uses to attach to cells before viral fusion and entry into host cells. Maraviroc (MVC, Selzentry) is a CCR5 antagonist that inhibits the HIV-CCR5 interaction and thereby prevents HIV from entering the cells. Many treatment-experienced patients may have non-CCR5-tropic virus. Thus, screening patients with tropism assays (e.g., Trofile) before maraviroc initiation is essential.

 

Integrase Inhibitors (or integrase strand transfer inhibitors (INSTIs))

Integrase is a key viral enzyme that facilitates integration of retroviral DNA into the host cell genome. Drugs of this family inhibit this process, thereby preventing viral replication.

    Dolutegravir (Tivicay)

    Elvitegravir (Vitekta)

    Raltegravir (Isentress)

    Cabotegravir (Vocabria)

 

Attachment Inhibitors

This new class  of HIV drugs blocks viral attachment to the host CD4 molecule on T-lymphocytes.

Fostemsavir was the first example of this class to be approved by the FDA (in 2020). It is indicated for HIV infections that cannot be successfully treated with other ARTs because of resistance, intolerance or safety considerations. 

 

Capsid Inhibitors

Drugs with this mechanism of action block capsid protein oligomerization and disrupt interactions with host factors that are crucial for both early and late phases of the viral replication cycle. Lenacapavir was the first drug of this class to be approved for clinical use (in 2022, by the EMA & FDA). It is a long-acting drug that's administered as a subcutaneous depot injection, once every 6 months. It is prescribed in combination with other antiretrovirals. Like Fostemsavir, lenacapavir's use is reserved for HIV infections that cannot be successfully treated with other ARTs because of resistance, intolerance or safety considerations. 

 

Fixed-Dose combination HIV medications

    Abacavir + dolutegravir + lamivudine, or ABC/DTG/3TC (Triumeq)

    Abacavir + lamivudine, or ABC/3TC (Epzicom)

    Abacavir + lamivudine + zidovudine, or ABC/3TC/ZDV (Trizivir)

    Efavirenz + emtricitabine + tenofovir, or EFV/FTC/TDF (Atripla, Tribuss)

    Elvitegravir + cobicistat + emtricitabine + tenofovir, or EVG/COBI/FTC/TAF or ECF/TAF (Genvoya)

    Elvitegravir + cobicistat + emtricitabine + tenofovir, or EVG/COBI/FTC/TDF or ECF/TDF (Stribild)

    Emtricitabine + rilpivirine + tenofovir, or FTC/RPV/TAF (Odefsey)

    Emtricitabine + rilpivirine + tenofovir, or FTC/RPV/TDF (Complera)

    Emtricitabine + tenofovir, or TAF/FTC (Descovy)

    Emtricitabine + tenofovir, or TDF/FTC (Truvada)

    Lamivudine + zidovudine, or 3TC/ZDV (Combivir)

    Cabotegravir + rilpivirine (Cabenuva; co-packaged) is a once monthly injectable regimen for uncomplicated infections.

 

ART adherence is essential to prevent drug-resistant strains of HIV developing. If ART is used properly HIV-positive patients can now live long, active lives.

Prescribing decisions are reached by considering existing medical conditions, immune system function, and should involve discussions about which regimen the patient would prefer, and would be most likely to adhere to.

 

Pre-exposure prophylaxis (or PrEP) is the most recent advance in ART, with the approval of Truvada as a therapy to reduce the likelihood of HIV infection in high risk individuals (e.g. to reduce the risk of HIV-negative people getting HIV from a sexual or injection-drug-using partner who is HIV-positive). The CDC (https://www.cdc.gov/hiv/basics/prep.html) reported that among people who inject drugs, PrEP reduces infection risk by >70%. If combined with ‘safe sex’ the risk of getting sexually transmitted HIV whilst taking PrEP is reduced by up to 90%.

 

Ongoing Drug Development

Drugs with alternative modes of action are being sought to overcome the problems associated with acquired drug-resistance.

For example, PRO 140 is a humanized monoclonal antibody targeted against the CCR5 receptor. In Phase 3 clinical trial.

This is an immunology website based in South Africa, in partnership with the International Union of Immunological Societies (IUIS), that has a strong emphasis on HIV and AIDS. The website offers Teaching and Learning Tools (including core immunology modules) as well as a Treatment & Diagnostics section that includes HIV-specific topics such as HIV Life Cycle, Declining CD4 count and ARV Drug Information.

Average: 3.3 (6 votes)

Drugs for viral hepatitis- HBV and HCV

Hepatitis B

Hepatitis B is an infectious disease caused by the hepatitis B virus (HBV). It can cause both acute and chronic infections. Most cases of chronic disease are asymptomatic, however, cirrhosis and liver cancer may eventually develop. HBV is transmitted by exposure to infectious blood or body fluids. The infection can be diagnosed 30 to 60 days after exposure. HBV infection has been preventable by vaccination since 1982, with two or three doses required to achieve full protection. Natural life-long resistance develops following infection.

During initial infection, care is based on the patient’s symptoms. As an exception, early antiretroviral therapy may be indicated for cases of aggressive (fulminant) hepatitis or when the patient is immunocompromised. In those who develop chronic disease, antiviral medication such as tenofovir or interferon may be useful to reduce the risk of cirrhosis and liver cancer. The drugs available cannot clear the infection, rather they inhibit viral replication to limit liver damage. The World Health Organization recommended a combination of tenofovir and entecavir as first-line agents.

Drugs approved for HBV infection include

adefovir (Hepsera)

entecavir (Baraclude)

lamivudine (Epivir)

telbivudine (Tyzeka)

tenofovir (Viread)

and the two immune system modulators interferon alpha-2a and PEGylated interferon alpha-2a (Pegasys)

 

Hepatitis C

Hepatitis C is an infectious disease caused by the hepatitis C virus (HCV). Few symptoms are evident during the initial period of infection, or even when disease has progressed to early chronic infection. Damage accumulates over time and can lead to liver disease, cirrhosis and liver cancer. HCV is spread primarily by blood-to-blood contact (e.g. associated with intravenous drug use, poorly sterilized medical equipment, needlestick injuries in healthcare, blood transfusions, and mother-to-child transmission).

There is no vaccine against hepatitis C, however chronic HCV infection can be effectively managed about 95% of the time with antiviral medications. HCV treatment focusses on management rather than cure. Treatment aims are:

  • eradication of virus
  • decreasing morbidity and mortality
  • normalization of biochemical markers
  • improving clinical symptoms
  • preventing spread of the disease
  • preventing progression to cirrhosis and hepatocellular carcinoma
  • preventing the development of end-stage liver disease and its manifestations

 

How do anti-HCV drugs work?

See further analysis of 'The ins and outs of hepatitis C virus entry and assembly' by Lindenbach and Rice (2013) PMID: 24018384

 

Direct-acting hepatitis C virus antiviral agents

Ledipasvir inhibits the HCV NS5A protein necessary for viral replication.

Ombitasvir is an HCV NS5A replication complex inhibitor, and interferes with viral RNA replication and virion assembly.

Pibrentasvir is a NS5A Inhibitor (prescribed in a fixed-dose formulation with glecaprevir).

Paritaprevir inhibits HCV NS3/4A protease and interferes with HCV coded polyprotein cleavage necessary for viral replication.

Glecaprevir is also a NS3/4A protease inhibitor (prescribed in a fixed-dose formulation with pibrentasvir).

Ribavirin is a synthetic nucleoside analogue with antiviral activity. It MUST be used in combination with an interferon product. Ribavirin monotherapy is not effective for the treatment of chronic HCV infection and should not be used alone for this indication. The mechanism by which the combination of ribavirin + interferon exerts its anti-HCV effects has not been fully established.

Simeprevir, like ribavirin is not effective as a monotherapy, and must be used in combination with peginterferon alfa and ribavirin, or with sofosbuvir. Mechanistically, simeprevir is an inhibitor of HCV NS3/4A protease, a protease that is essential for viral replication.

Sofosbuvir is a prodrug converted to its pharmacologically active form (GS-461203, a nucleoside (uridine) analog triphosphate) that acts as an inhibitor of HCV NS5B RNA-dependent RNA polymerase, acting as a chain terminator during viral replication.

Velpatasvir is an HCV NS5A replication complex inhibitor, and interferes with viral RNA replication and virion assembly.

Voxilaprevir is an inhibitor of HCV NS3/4A protease, a protease that is essential for viral replication.

Indirect anti-HCV drugs

Ritonavir is not active against HCV directly. Ritonavir is a potent CYP3A inhibitor that increases peak and trough plasma drug concentrations of paritaprevir and overall drug exposure (i.e. AUC).

 

There are at least six genetically distinct HCV genotypes, or strains. Knowing the strain of the virus can help inform treatment recommendations. Treatment during the first six months is more effective than once chronic infection has established.

HCV genotypes
HCV genotype Recommended treatment regimen Alternative treatment regimen
1a 12 weeks of ledipasvir + sofosbuvir 12 to 24 weeks of paritaprevir + ombitasvir + dasabuvir + ribavirin
1b 12 weeks of ledipasvir + sofosbuvir 12 weeks of paritaprevir + ombitasvir + dasabuvir
2 12 to 16 weeks of sofosbuvir and ribavirin  
3 12 weeks of sofosbuvir + ribavirin + pegylated interferon  
4 12 weeks of ledipasvir + sofosbuvir or paritaprevir + ritonavir + ombitasvir + ribavirin 24 weeks of sofosbuvir + ribavirin
5 or 6 sofosbuvir + ledipasvir  

Recommendations based on AASLD/IDSA HCV Guidance, Panel (September 2015). PMID 26111063

  • sofosbuvir + ribavirin + interferon is ~90% effective in those with genotype 1, 4, 5, or 6 disease
  • sofosbuvir + ribavirin is 70-95% effective in type 2 and 3 disease but has a higher rate of adverse effects.
  • ledipasvir + sofosbuvir for genotype 1 is 93-99% effective but is very expensive
  • pegylated interferon + ribavirin- is 60-90% effective in genotype 6 infection

Latest drug approvals:

Vosevi (FDA approval in July 2017), is a fixed-dose, combination tablet containing two previously approved drugs (sofosbuvir and velpatasvir), and a new drug, voxilaprevir. Approved for use in adults with chronic hepatitis C virus (HCV) genotypes 1-6 without cirrhosis or with mild cirrhosis, including re-treatment of patients previously treated with the direct-acting antiviral drug sofosbuvir or NS5A inhibitors. This new approval represents a treatment option for those patients who were not successfully treated with other HCV drugs. Treatment recommendations for Vosevi are different depending on viral genotype and prior treatment history. The most common adverse reactions are headache, fatigue, diarrhoea and nausea. Vosevi is contraindicated in patients taking the drug rifampin. Hepatitis B virus (HBV) reactivation is a potentially life-threatening Vosevi-associated event in HCV/HBV coinfected patients, so patients should be screened for evidence of current or prior HBV infection before starting treatment with Vosevi.

Mavyret (FDA approval in August 2017), is a fixed-dose, combination tablet containing glecaprevir and pibrentasvir. It's approved for the treatment of adults with chronic hepatitis C virus (HCV) genotypes 1-6 without cirrhosis (liver disease) or with mild cirrhosis. It is also approved for HCV genotype 1 infections in patients who have previously been treated with either a NS5A inhibitor or an NS3/4A protease inhibitor (but not both). The recommended treatment regimen is eight weeks, which is shorter than the previous therapies which were administered for 12 weeks.

Drugs for cytomegalovirus (CMV) infection

The anti-human CMV drugs used currently target CMV replication via two distinct mechanisms.

pUL54 inhibitors

Ganciclovir (GCV; Cytovene) is a nucleoside analogue. It must be phosphorylated (to the nucleotide) by the viral protein kinase, pUL97 to confer anti-viral activity. Use of GCV as prophylaxis for CMV is limited by clinically significant myelosuppression. GCV is more commonly used to treat CMV retinitis, usually in patients who have suppressed immune systems (e.g. AIDS patients and solid organ transplant patients). It is also used to treat ocular ulcers caused by the herpes simplex virus.

Valganciclovir (Valcyte) is a GCV prodrug, that is generally used to prevent CMV reactivation or infection that may occur after a solid organ transplant. Like ganciclovir it causes significant myelosuppression.

Cidofovir (CDV), on the other hand is a nucleotide analogue, and does not need modification for activity. Cidofovir is only used to treat CMV retinitis in AIDS patients.

Foscarnet (FOS) inhibits pUL54 activity by binding to the enzyme's pyrophosphate binding site. It is used to treat CMV retinitis in AIDS patients and HSV infection in immunocompromised patients after failure to respond to other antiviral drugs.

Mutations in either pUL97 or pUL54 can result in resistance against these three drugs. Most cases of resistance to GCV are due to mutations in the UL97 gene, but mutations in the UL54 gene can also cause antiviral resistance. The problem of resistance to current drugs has been addressed by the development of compounds with an alternative mechanism to disrupt viral replication.

Viral terminase inhibitor

Letermovir (Prevymis) is the most recently approved anti-CMV medication (FDA approval granted in November 2017, and EMA marketing authorisation in January 2018). Letermovir inhibits the viral terminase complex (which consists of the CMV-encoded proteins pUL51, pUL56, and pUL89), which is a DNA packaging unit that is essential for DNA-containing viral capsid formation. By inhibiting terminase activity (by binding to pUL51 and/or pUL56), letermovir prevents CMV replication. This drug can be administerd orally or by i.v. infusion. It is approved as prophylaxis for CMV in allogeneic hematopoietic-cell transplantation patients who are receiving immunosuppressant therapy. It prevents CMV reactivation in these patients (see PMID: 29211658).

Average: 3.2 (13 votes)

Antimycotic drugs

Antimycotic drugs, also known as antifungal drugs, are utilised to treat various fungal infections including yeast infections, athlete's foot, onychomycosis (fungal nail infections), ringworm, oropharyngeal, skin, vaginal and vulval fungal infections. These drugs exert their effects by targeting specific components of fungal cells, such as the cell wall or membrane, to inhibit their growth, survival, and reproductive capacity.

The administration of antimycotic drugs can be oral, topical, or intravenous, depending on the specific drug, as well as the severity and location of the infection. It is important to note that some antimycotic drugs may have side effects, such as liver toxicity or gastrointestinal upset, and may interact with other medications. Therefore, careful monitoring is necessary during treatment. The emergence of antimycotic drug resistance, exemplified by strains of Candida auris, is a growing concern. Appropriate use and monitoring of these drugs are crucial to prevent the development of resistant fungal strains. As with antibacterial medications, it is essential to complete prescribed drug courses.

Antimycotic drugs are commonly classified into four major categories:

  1. Azole class drugs inhibit the synthesis of ergosterol, a vital component of fungal cell membranes.
  2. Polyenes bind to ergosterol in the fungal cell membrane, causing it to become permeable and leading to fungal cell death.
  3. Echinocandins target the fungal cell wall by inhibiting the synthesis of beta-glucan, an essential component of fungal cell wall formation.
  4. The ‘other’ antimycotics group includes the pyrimidine analogue flucytosine (which interferes with fungal DNA and RNA synthesis), along with terbinafine, griseofulvin and ibrexafungerp.

This classification system helps categorise and understand the mechanisms of action of different antimycotic drugs.

1. Azole antimycotics:

Azole antimycotics are synthetic, fungistatic agents with broad-spectrum activity. They all share a common chemical structure called an azole ring and can be further subclassified into imidazoles (with two nitrogens in the azole ring), or triazoles (with three nitrogens in the azole ring)- as shown in the table below.

Imidazoles Triazoles
clotrimazole, econazole, ketoconazole, miconazole, tioconazole fluconazole, itraconazole, posaconazole, voriconazole, isavuconazonium, isavuconazole

Additionally, oteseconazole is in a subclass of its own, as the first approved azole antifungal drug to possess a tetrazole moiety, which consists of an azole ring with four nitrogens.

Azole antimycotic drugs are widely utilised for the treatment of various fungal infections. They offer a broad spectrum of activity and are indicated for a wide range of clinical conditions. Below, we provide an overview of several frequently used azole antimycotics, detailing their clinical uses and potential side effects:

  • Fluconazole: This drug is widely employed to treat a variety of fungal infections, including candidiasis, cryptococcosis, and dermatophytosis. It can be administered orally or intravenously and generally exhibits a relatively low incidence of side effects. Some possible side effects include gastrointestinal upset, rash, and headache.
  • Itraconazole: Used for a range of fungal infections, such as candidiasis, aspergillosis, and histoplasmosis. Itraconazole can be administered orally or intravenously. Compared to fluconazole, it has a higher incidence of side effects, and these may include gastrointestinal upset, liver toxicity, and cardiovascular effects.
  • Voriconazole: As a second-generation triazole. voriconazole is primarily employed to treat invasive aspergillosis and other serious fungal infections. It can be administered orally or intravenously. Voriconazole has a higher incidence of side effects than fluconazole, including visual disturbances, skin reactions, and liver toxicity.
  • Posaconazole: This third-generation triazole treats a range of fungal infections, including candidiasis, aspergillosis, and mucormycosis. It can be administered orally or intravenously and generally has a relatively low incidence of side effects. Possible side effects may include gastrointestinal upset and headache.
  • Isavuconazole: Acting as triazole, isavuconazole inhibits fungal cell division and disrupts ergosterol synthesis. It is utilised for the treatment of invasive aspergillosis and mucormycosis. It can be administered orally or intravenously and has a relatively low incidence of side effects. Possible side effects can include gastrointestinal upset and headache.

Each azole antimycotic drug has its own unique clinical use and potential side effects profile. It is important for healthcare professionals to carefully consider these factors when selecting the appropriate drug for each patient.

2. Polyene antimycotic drugs:

Polyene antimycotic drugs are a class of medications that have been used for several decades to treat fungal infections. Their primary mechanism of action involves binding to ergosterol, a key component of fungal cell membranes, resulting in membrane disruption and cell death. The following summary provides information on commonly used polyene antimycotics, their intended uses, and potential side effects:

  • Amphotericin B: This broad-spectrum antimycotic drug has been in use since the 1950s to treat various systemic fungal infections. It is available in different formulations, including a conventional formulation (amphotericin B deoxycholate) and lipid formulations (amphotericin B lipid complex, amphotericin B colloidal dispersion, and liposomal amphotericin B). The lipid formulations, which are less nephrotoxic, have replaced the conventional formulation in many clinical settings. Amphotericin B is administered intravenously and has a high incidence of side effects, such as fever, chills, hypotension, nephrotoxicity, and electrolyte imbalances.
  • Nystatin: This topical antimycotic drug is used to treat fungal infections of the skin, mouth, and intestinal tract. It is not systemically absorbed, resulting in a low incidence of side effects. Nystatin is available in various forms, including creams, ointments, and oral suspensions.
  • Natamycin: This topical antimycotic drug is used to treat fungal infections of the eye, including blepharitis, conjunctivitis, and keratitis caused by susceptible fungi, such as Fusarium solani. It is administered as an ophthalmic solution with a low incidence of side effects. However, its efficacy as a single agent for treating fungal endophthalmitis (infection of the vitreous and aqueous intraocular fluids) has not not been established.

The clinical use of polyene antimycotic drugs can be limited by their high incidence of side effects. Therefore, healthcare professionals must carefully consider the potential risks and benefits when prescribing these medications.

3. Echinocandin antimycotic drugs:

Echinocandins are a class of antimycotic drugs that target the fungal cell wall. They are lipopeptide molecules that noncompetitively inhibit a fungal enzyme crucial for 1,3-beta-D-glucan synthesis, disrupting cell wall formation. Due to poor absorption from the gastrointestinal tract these drugs are administered by slow intravenous infusion. A slow infusion rate is essential to minimise the risk of histamine-mediated reactions.

  • Micafungin: A semisynthetic echinocandin that is used in the treatment of candidaemia (Candida infections in the blood), acute disseminated candidiasis, Candida peritonitis and abscesses, oesophageal candidiasis, and as prophylaxis of Candida infections in patients who are receiving haematopoietic stem cell transplants.
  • Anidulafungin: Used to treat candidaemia and other invasive Candida infections such as those in the stomach and oesophagus.
  • Caspofungin: Used to treat fungal infections of the stomach, lungs and oesophagus, including intra-abdominal abscess, peritonitis, and pleural space infections. Effective against C. albicans, C. glabrata, C. krusei, C. parapsilosis, and C. tropicalis.

4. Other antimycotic drugs:

  • Terbinafine: An oral antimycotic drug that is used to treat dermatophyte infections of the fingernails or toenails (onychomycosis), and hair follicles. It is more active against dermatophytes than azole class drugs, but less active than azole antimycotics against Candida infections. Hepatotoxicity is an established severe side effect, so this drug is not suitable for patients with liver disease. Terbinafine inhibits CYP2D6; therefore pharmacokinetic interactions are possible with drugs that are substrates for CYP2D6 (e.g., tricyclic antidepressants, β-blockers, selective serotonin reuptake inhibitors [SSRIs], monoamine oxidase [MAO] inhibitors).
  • Griseofulvin: An oral antimycotic antibiotic that is produced by Penicillium sp. It is administered orally to treat infections such as ringworm, athlete's foot, jock itch, and fungal infections of the scalp (Tinea capitis), fingernails, or toenails. Griseofulvin is not suitable for patients with porphyria or liver failure, nor should it be prescribed during the first 3 months of pregnancy as it is potentially embryotoxic and teratogenic and may harm the unborn baby. The primary use of griseofulvin is as a treatment for severe, chronic, or recalcitrant Tinea dermatophytoses, when topical antimycotic treatment has failed to clear the infection.
  • Ibrexafungerp: An orally administered triterpenoid used to treat recurring (post-menarchal) vaginal yeast infections. It carries a high risk of embryo-fetal toxicity, so is contraindicated during pregnancy.
  • Flucytosine: A fluorinated pyrimidine analogue. It is an oral antimycotic that is used to treat severe Candida infections of the blood, lungs, heart, central nervous system, and urinary tract (especially fluconazole-resistant strains), sometimes along with intravenous amphotericin B, and to treat serious cryptococcal infections (cryptococcosis) including pulmonary infections, septicaemia, and meningitis, again, usually in conjunction with intravenous amphotericin B.

The World Health Organization (WHO) Essential Medicines List (EML) includes several antimycotic drugs considered essential for addressing fungal infections in the global population.

The antimycotic drugs included in the WHO Essential Medicines List are:

  • Amphotericin B
  • Anidulafungin
  • Caspofungin
  • Clotrimazole
  • Fluconazole
  • Flucytosine
  • Griseofulvin
  • Itraconazole
  • Micafungin
  • Nystatin
  • Potassium iodide
  • Voriconazole

Antimycobacterial drugs

The most common mycobacterial infections globally are tuberculosis (TB) and leprosy.

Tuberculosis is a bacterial infection caused by the bacterium Mycobacterium tuberculosis. It primarily affects the lungs, but can also affect other parts of the body. According to the World Health Organization (WHO), there were an estimated 10 million cases of TB worldwide in 2020, with the highest burden of disease in Asia and Africa.

Leprosy (or Hansen's disease) is a chronic bacterial infection caused by Mycobacterium leprae. It primarily affects the skin and peripheral nerves, but can invade other organs and tissues. WHO data from 2020 indicate that the highest burden of disease is in India, Brazil, and Indonesia.

Other less common mycobacterial infections include nontuberculous mycobacterial infections (e.g., M. kansasii, M. marinum, M. ulcerans and M. xenopi), and M. avium complex (MAC) infections that primarily affect people with weakened immune systems.

Several drugs are currently in clinical use for the treatment of these infections. These drugs differ in their mechanisms of action and prescribing information. Summarized details for each medication are provided below.

  • Isoniazid is a first-line antituberculosis drug that works by inhibiting mycolic acid synthesis, a critical component of the mycobacterial cell wall. It is administered orally and is generally well-tolerated. However, it can cause hepatotoxicity and peripheral neuropathy, especially in patients with underlying liver disease or diabetes.
  • Rifampin is another first-line orally administered antituberculosis drug. It acts to inhibit bacterial DNA-dependent RNA polymerase activity. Rifampin is bactericidal against M. leprae and it is the main constituent of multiple-drug regimens used for treatment of leprosy; other drugs are included in the regimens to prevent emergence of rifampin-resistant M. leprae. Can be used (off-label) for the treatment of MAC pulmonary infections in conjunction with other antimycobacterials. Rifampin can cause a number of side effects, including hepatotoxicity, gastrointestinal disturbance, and hematologic effects that can include thrombotic thrombocytopenic purpura and hemolytic uremic syndrome.
  • Pyrazinamide is a first-line antituberculosis drug that works by disrupting the energy metabolism of mycobacteria. It is administered orally and can cause hepatotoxicity and hyperuricemia.
  • Ethambutol is a second-line antituberculosis drug that works by inhibiting bacterial cell wall synthesis. It is administered orally and can cause optic neuritis, which can lead to vision loss.
  • Streptomycin is an aminoglycoside antibiotic that is used in combination with other antituberculosis drugs to treat multidrug-resistant TB. It inhibits bacterial protein synthesis. It is administered intramuscularly and can cause ototoxicity and nephrotoxicity.
  • Dapsone is used to treat leprosy as a component of multidrug therapies (MDT). MDT regimens can quickly clear the infection, reduce the risk of transmission, and delay or prevent emergence of resistant M. leprae. A two-medicine MDT (dapsone and rifampicin) is used to treat paucibacillary (or tuberculoid) leprosy and a three-drug MDT (dapsone, rifampicin and clofazimine) to treat multibacillary (or lepromatous) leprosy.

The World Health Organization (WHO) Essential Medicines List (EML) includes several antimycobacterial drugs that are considered essential for the treatment of tuberculosis (TB) and other mycobacterial infections. These drugs are included in the EML because they are effective, safe, and affordable, and are essential for addressing global health needs.

 

Links to the online EML lists of TB and leprosy drugs: