In vivo Metabolism of Ranitidine Catalyzed by Flavin-Containing Monooxygenase in Human

초록

Ranitidine, and H2 receptor antagonist used clinically for treatment of ulcer patients, is known to be oxidize to its N-oxide and S-oxide metabolites by the flavin-containing monooxygenase (FMO) contained in human liver microsomes. In an effort to develop a non-invasive assay method determining the in vivo hepatic FMO activity useful in phenotyping human, we have compared the ranitidine metabolites produced in vitro (by human liver microsomes) and in vivo (present in plasma and urine). For the in vivo metabolism, the volunteers were given 150 mg ranitidine and their plasma and urine samples were taken at each hour for up to 7 hr after the oral administration. After centrifugation of these in vitro and in vivo metabolism samples (100,000xg for 1 hr), the supernatant aliquots were loaded onto an HPLC column (Nova-Pak C18, 3.9X150 mm) and eluted with CH3CN solvent (10% to 70% gradient) containing 5 mM NaH2PO4 (pH 8.0). The retention times for ranitidine N-oxide, S-oxide, demethylranitidine metabolites and the unmetabolized ranitidine which were all detected using 320nm UV detector were 4.6 min, 6.4 min, 9.8 min and 13.9 min, respectively. The detection limit for all metabolites was 10 ng. Utilizing this newly developed facile ultracentrifugation sample preparation method which do not require the tedious organic solvent extraction, we are in the process of developing a non-invasive phenotyping method to determine the in vivo FMO activity in human.