Pharmacokinetics

Abstract

Drug level monitoring, when appropriately used, is of considerable help in optimising treatment and assuring adherence. In psychiatry, target ranges for psychotropic drug concentrations should be treated with some caution. Plasma levels of olanzapine are linearly related to daily dose, but there is substantial variation, with higher levels seen in women, non‐smokers and those on enzyme inhibiting drugs. Postmortem redistribution tends to be greater with drugs with a large volume of distribution especially when given over a long period during life. In most developed countries, clozapine blood concentration monitoring is widely used. Information on the effect of drugs on cytochrome function helps predict or confirm suspected interactions which may not have been uncovered in regulatory trials or in clinical use. The effects of polymorphism and pharmacokinetic interaction are difficult to predict because some drugs are metabolised by more than one enzyme and an alternative pathway(s) may compensate if other enzyme pathways are inhibited.