Anomalous results of studies on drug interaction in man. II. Halofenate (mk-185) and antipyrine, bishydroxycoumarin, and warfarin.

Three highly reproducible experiments on drug interaction in normal human volunteers provided anomalous results: chronic halofenate administration shortened plasma antipyrine and bishydroxycoumarin half-lives but prolonged plasma warfarin half-lives. This dissociation in the effect produced by a chronically administered drug on the metabolism of test drugs has not previously been reported in man. Chronic halofenate administration to rats, mice and dogs stimulated several hepatic microsomal drug-metabolizing systems, including those responsible for bishydroxycoumarin warfarin hydroxylation.