Effect of hepatic CYP inhibitors on the metabolism of sildenafil and formation of its metabolite, N-desmethylsildenafil, in rats in vitro and in vivo
ABSTRACT It has been reported that hepatic cytochrome P450 (CYP)2C9 and CYP3A4 are responsible for the metabolism of sildenafil and formation of its metabolite, N-desmethylsildenafil, in humans. However, in-vivo studies in rats have not been reported.
Sildenafil (20 mg/kg) was administered intravenously to rats pretreated with sulfaphenazole, cimetidine, quinine hydrochloride or troleandomycin, inhibitors of CYP2C6, CYP2C11, CYP2D subfamily and CYP3A1/2, respectively. In-vitro studies using rat liver microsomes were also performed.
The area under the plasma-concentration time curve (AUC) was increased and clearance of sildenafil decreased in rats pretreated with cimetidine or troleandomycin. The AUC ratio for N-desmethylsildenafil (0-4 h) : sildenafil (0-infinity) was significantly decreased only in rats pretreated with cimetidine. Similar results were obtained in the in-vitro study using rat liver microsomes.
Sildenafil is metabolised via hepatic CYP2C11 and 3A1/2, and N-desmethylsildenafil is mainly formed via hepatic CYP2C11 in rats. Thus, rats could be a good model for pharmacokinetic studies of sildenafil and N-desmethylsildenafil in humans.
XIII International Conference on Instrumental Analysis, Barcelona; 11/2011
- "Results that are supported by previous pharmacokinetic studies, in which SDF administered orally to rats showed that the principal route of metabolism of SDF is the N-demethylation mediated by cytochrome P450 3A1/2 and 2C11, with desmethylSDF as the major circulating metabolite  . However, our data also demonstrated the presence of O-desethylSDF, a metabolite of SDF that did not correspond with the rat plasma metabolites previously described. "
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ABSTRACT: The effects of regular organic solvents on the metabolic activities of various human cytochromes P450 (P450s) have been reported. However, very little is known about their influence on metabolic activities mediated by P450s in the rat liver microsomes (RLM). The purpose of this study was to investigate the effects of organic solvents such as methanol, acetonitrile, dimethyl sulfoxide (DMSO), acetone, and ethanol on CYP1A, CYP2C, CYP2D, CYP2E, and CYP3A-mediated metabolism using RLM. The results showed that the activities of most rat P450 enzymes appeared to be organic solvent-dependent, and the metabolism of the tested probes were remarkably reduced when the concentration of organic solvents was up to 5% v/v, whereas most organic solvents demonstrated no significant interference when the concentration was below 1%, with the exception of DMSO. In addition, organic solvents exhibited different inhibitory effects, for example, CYP2D and CYP2E showed a significant reduction of activities at lower concentrations of organic solvents. Hence, this phenomenon should be taken into consideration when designing in vitro metabolism studies of new chemical entities. Therefore, we recommend acetonitrile as the most suitable solvent for RLM incubations, and the content of organic solvent should be kept lower than 1% v/v.Drug metabolism and disposition: the biological fate of chemicals 11/2010; 38(11):1922-5. DOI:10.1124/dmd.110.033894 · 3.33 Impact Factor
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ABSTRACT: Pharmacokinetics of sildenafil and its metabolite, N-desmethylsildenafil, in humans and rats with liver cirrhosis (LC) and diabetes mellitus (DM), alone and in combination (LCD) did not seem to be reported. Sildenafil was administered intravenously (10 mg/kg) and orally (20 mg/kg) to control, LC, DM, and LCD rats. Expression of intestinal CYP isozymes in those rats was also measured. In LC, DM, and LCD rats, the areas under the curve (AUCs) of intravenous sildenafil were significantly greater (by 195%, 54.2%, and 127%, respectively) than controls. In LC and LCD rats, AUCs of oral sildenafil were significantly greater (3010% and 2030%, respectively) than controls. In LC, DM, and LCD rats, significantly greater AUCs of intravenous sildenafil were due to the slower hepatic extraction of sildenafil (because of decrease in the protein expression of hepatic CYP2C11 and 3A subfamily in LC and LCD rats, and CYP2C11 in DM rats). In LC and LCD rats, greater magnitude of increase in AUCs of oral sildenafil than those after the intravenous administration could be mainly due to the decrease in the intestinal extraction of sildenafil (because of decrease in the protein expression of intestinal CYP2C11 in LC and LCD rats).Xenobiotica 11/2010; 41(2):164-74. DOI:10.3109/00498254.2010.532885 · 2.10 Impact Factor