Therapeutic drug monitoring
Prescribers choose treatment regimens on the basis that the benefits that accrue will outweigh the adverse effects. However, that outcome is never certain for individual patients even if the best evidence suggests that it is likely. The uncertainty arises for many of the reasons outlined in previous sections (e.g. pharmacodynamics, pharmacolkinetics, pharmacogenetics). For this reason, whenever possible, prescribers should try to measure the effects of the drug, beneficial and harmful. This will help to inform decisions about dose titration (up or down) or discontinuation of treatment. Monitoring can be achieved in several different ways. It might be achieved subjectively be asking the patient about their symptoms. More objective approaches might be to measure the actual clinical effect. If this is not possible then alternatives are to measure a biomarker that acts as a surrogate for the clinical endpoint. Alternatively, if the pharmacodynamic effects of the drug are difficult to assess then it may be possible to measure the plasma drug concentration on the basis that it will be closely related to the effect of the drug.