The regulatory view on drug-drug interactions.

Nowadays the majority of patients receive more than one drug simultaneously. Since drug-drug interactions and side-effects increase in a nonlinear fashion with the number of drugs administered, a drug, which might interact with a commonly used comedication should be tested specifically and systematically in this regard before marketing. So far no regulatory framework precisely defines the requirements and the design of particular drug interaction studies. The directions and guidelines of the European Community contain only general outlines about preferred study designs and the necessity of drug interaction studies. Valuable information can be found in the Guideline Special Population of the International Conference on Harmonization (ICH). On the other hand, the general character of existing regulations enables the researcher to apply the most suitable approach to uncover therapeutically relevant interactions of a new drug before marketing. After marketing approval postmarketing surveillance is necessary to detect further drug interactions of clinical relevance.