The metabolism of roxatidine acetate hydrochloride in rat and dog liver homogenates

The metabolites were identified by gas chromatography-mass spectrometry (GC-MS). When an equimolar mixture of roxatidine acetate hydrochloride and its deuterated compound, labeled with ten deuterium atoms in the piperidine ring, was incubated with the 9000×g supernatant (S-9) fraction of either rat or dog liver homogenate, the oxygenated metabolites of the piperidine ring such as the 3-hydroxypiperidine derivative (M1) and the 2-oxopiperidine derivative (M2) were isolated from rats but M2 was not isolated from dogs. These results suggested that the species differences in the metabolism of the piperidine ring in vitro are similar to that in vivo. The deuterium isotope effect (H/D) was 1.34 for M1 and 1.47 for M2 in rats, while the value for M1 in dogs was 1.69. On the other hand, the formation of these oxidative metabolites was inhibited by carbon monoxide in incubations using hepatic microsomes, suggesting that the reaction was catalyzed by cytochromes P-450.