Kinetics of ranitidine metabolism in dog and rat isolated hepatocytes

1. Freshly isolated hepatocytes from rat and dog have been evaluated as a model for the metabolism of ranitidine in vivo. 2. Isolated hepatocytes from the male and female dog and male Wistar and random hooded rat metabolized ranitidine to ranitidine N-oxide, ranitidine S-oxide, desmethylranitidine and two unidentified minor metabolites. The furoic acid metabolite of ranitidine, previously reported to be a minor metabolite in vivo in rat and dog, was not detected in hepatocytes from either species. 3. The kinetics for ranitidine metabolism in hepatocytes were monophasic for the formation of the three major metabolites in dog and Wistar rat and for N-demethylation of ranitidine in the random hooded rat, but biphasic in this latter strain for the N- and S-oxidation of ranitidine. 4. Ranitidine N-oxide was reduced to ranitidine by Wistar rat hepatocytes but not by hepatocytes from the random hooded rat or dog. Ranitidine S-oxide was metabolized by hepatocytes from both species to one of the unidentified metabolites but was not reduced to ranitidine in either species. Desmethylranitidine was not a substrate for metabolism in hepatocytes from either species. 5. The relative quantitative importance of ranitidine N-oxide, ranitidine S-oxide and desmethylranitidine produced by the hepatocytes was consistent with the profiles of these three metabolites in vivo in rat and dog. The results confirm the value of isolated hepatocytes as a predictive model for in vivo drug metabolism.