Further studies on medazepam metabolism in the rat

Previous studies with 9000g supernatant fractions of rat liver revealed that the 1,4-benzodiazepine, medazepam, was converted to N-desmethyldiazepam by a series of reactions including hydroxylation, N-demethylation, and dehydrogenation. The present study was designed to determine if the pathway via diazepam as intermediate, which is one of three possible pathways, is the major route in vivo in the rat for N-desmethyldiazepam formation from medazepam. Measurement of the levels of labeled drug and metabolites in blood, brain, lung, heart, and muscle 5 min after the oral administration of approximately equivalent doses of [14C]medazepam hydrochloride, [14C]diazepam, or N-desmethyl[14C]medazepam revealed that each drug was both rapidly absorbed and oxidatively metabolized in the rat. At 1 hr. the tissue levels of labeled N-desmethyldiazepam were highest after N-desmethyl-[14C]medazepam, intermediate after [14C]medazepam hydrochloride and lowest after [14C]diazepam. These results indicated that in the formation of N-desmethyldiazepam from medazepam in the rat there is a substantial preference for the pathway via N-desmethylmedazepam over that in which diazepam is an intermediate. From consideration of the limited data available, it is suggested that this same preference in pathways may also hold true in humans.