Important drug interactions in dermatology

Drug interactions can occur at any step from absorption to elimination of a drug, and can induce adverse as well as beneficial effects. Since systemic drugs are increasingly available and important in the treatment of dermatological diseases, a variety of possible interactions between concomitantly administered drugs have to be considered by dermatologists. The xenobiotic-metabolising enzyme system cytochrome P450 (CYP) is involved in the metabolism of many drugs, regulating their plasma concentrations and activities. Furthermore, the adverse effects of many drugs depend on the basal activity and inducibility of particular CYP isoenzymes in an individual patient. Since drug therapy in dermatological practice is of increasing complexity, and an increasing number of potent systemic drugs have become commonly used therapeutic agents, this review focuses on the following topics with the aim of optimising dermatological drug therapy. In the first section, all the different types of drug interactions that can occur through pharmacokinetic and pharmacodynamic mechanisms are introduced briefly, and then discussed systematically with special reference to drugs important for dermatologists. Then, the network of drug interactions that may occur from absorption to elimination is presented. The most important drug interactions mediated by CYP isoenzymes are listed. Finally, the importance of pharmacogenetics for the development of new drugs and its potential impact on the optimisation of individual therapy regimens is discussed.