Adverse drug reactions represent a common clinical problem. They are partly induced by a large variability in drug response, which results from the complex interplay between pharmacokinetics, pharmacodynamics and other disease-associated factors. The reviewde scribes metabolic changes caused by polymorfism in the cytochrome P450 and gives examples of induction and inhibition of this enzyme system in relation to adverse drug interaction. From the clinical point of view, attention should be paid especially to antidiabetics, anticoagulants and phenytoin. Therapeutic drug monitoring and genetic-based individualization of the therapy with polymorphically metabolized drugs with narrow therapeutic range can contribute to the decreased incidence of adverse drug reactions.

        Key words: adverse drug reactions, drug interactions, drug metabolism, genetic polymorfism.