[Interaction between drugs. A critical assessment of various controlling factors in relation to clinical significance--exemplified by cimetidine].

Interactions between pharmaceutical preparations are common and can occur at almost every stage in a substance's metabolic clearance but frequently lack clinical significance. Different factors must be considered in the assessment of data on interactions. This article compares interactions between H2-antagonists from various aspects: the disposition of the study, the mechanism of operation, the pharmacokinetics and pharmaco-dynamics etc. Several pharmaceutical interactions are dose-related so that the questions of equipotent dosage, the length of the period of treatment etc are crucial. The principal interaction mechanism for this group of drugs pertains to absorption, interference with the oxidative metabolism and excretion via the kidneys. Important measures to avoid interaction problems are individualization of the dose (lower dose = less risk), scrupulous clinical observation, and determination of the concentration in the blood of the drug concerned, if an analytical method exists. Under these circumstances any of the H2 antagonists may be used.