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Inter-individual variation in drug metabolism is a complicating factor, which affects drug therapy: it causes that the standard dose of drug may result in adverse drug reactions in some patients, or that drugs fails to work properly. In fact, adverse drug reactions are responsible for 7% of hospitalizations and are the 5th cause of death. In addition, only 25-60% of drugs are optimally effective.

Part of this inter-individual variation in drug response can be predicted by a simple DNA analysis, i.e. pharmacogenetics. A prominent role is played by cytochrome P450 enzymes (e.g. 2D6, 2C19), which are involved in the metabolism of 80% of all drugs. Knowledge about the genetic make-up of a patient enables dose adjustment prior to starting therapy. Thereby decreasing adverse drug reactions and increasing therapy efficacy, benefitting patient, health care provider and society. Currently, the FDA has included pharmacogenetics information in the drug label of over 100 drugs.

In this presentation, a general introduction into pharmacogenetics will be given: What is pharmacogenetics and what is the impact of Adverse Drug Reactions? What are Cytochrome P450 genes and what is the clinical relevance of testing with two examples of diagnostic assays? Finally, the current status of clinical pharmacogenetics in the Netherlands will be outlined as well as the implementation of pharmacogenetics into routine care.