Clinical Application of Therapeutic Drug Monitoring and Pharmacogenetics in Psychiatry, with a Focus on Belgium.

Response rate to treatment is generally not as high as expected in psychiatric disorders. The lack of clinical improvement under a well-conducted treatment, that complies with guidelines, may be the consequence of genetic abnormalities that impact the metabolizing pathways of the drug. Genetic polymorphism of metabolizing enzymes is frequent in the population and has been proven to have a clinical impact. It may also be the consequence of environmental or organic factors that interact with the pharmacokinetic pathways (absorption, distribution, metabolizing, excretion) of the drug. These intrinsic and extrinsic factors will lead to inter- and intraindividual fluctuations in plasma drug concentrations. Therapeutic drug monitoring permits to measure plasma drug concentrations in order to adapt psychopharmacotherapy individually. In some cases, it can be coupled to pharmacogenetic testings. This review presents recent literature and guidelines on the subject. Eventually, there is a focus made on the French-speaking part of Belgium where neither therapeutic drug monitoring, nor pharmacogenetics testing, are used frequently in clinical practice. Some challenges are to be addressed to implement these techniques in Belgium.