[Optimisation of psychopharmacological treatment strategies by using therapeutic drug monitoring].

The effect of a (neuro-)psychopharmacological drug is determined by its interaction with its target structure in the brain (pharmacodynamics). A number of pharmacokinetic factors determine whether a drug is capable of reaching its site of action in a sufficient concentration. The concentration of the active compound can be significantly affected by its metabolism, which is genetically determined in each individual (known as the pharmacokinetic genotype), and by potential interactions with other prescribed drugs (known as the pharmacokinetic phenotype). For example, changes in drug metabolism inevitably lead to changes in the concentration of active compounds and thus to changes in the exposure of the drug. Therapeutic drug monitoring (TDM) is a tool for individualized pharmacotherapy that helps to optimize pharmacological treatment. On the one hand, TDM helps to detect deviations from expected drug concentrations and individualize treatment by adjusting doses. On the other hand, looking at the ratio of the parent compound and its metabolite (known as the metabolic ratio) helps to identify any abnormalities or peculiarities in drug metabolism supporting dose adjustments. This article provides a clinically oriented overview of how changes in drug metabolism can lead to treatment failure and which tools can be used to optimize treatment.