Determination of nimodipine and its dehydrogenation metabolite in human liver microsome by HPLC and its metabolizing kinetics

AIM: To develop an HPLC method for the determination of nimodipine and its major metabolite as well as the kinetics of its metabolism in human liver microsomes. METHODS: Chromatography was performed on an Hypersil BDS C₁₈ column. An acetonitrile-water(62:38) mixture as the mobile phase was used with the UV detector set at 238 nm. Following alkalinization with NaOH human liver microsomes were extracted with n-hexane-ether(1:1). RESULTS: The recovery of of nimodipine and its major metabolite for the proposed method was more than 94.3%. The relative standard deviations for within-day and between-day were <9.68%. The calibration curve was linear in the range from 1.31 to 20.92 μg·mL^-1 with γ = 0.9997 for nimodipine and from 122.7 to 4908.0 ng·mL^-1 with γ = 0.9995 for its dehydrogenation metabolite. The elimination of nimodipine and the formation of dehydrogenation metabolite was linear. CONCLUSION: Nimodipine was rapidly metabolized to its dehydrogenated metabolite in human liver microsomes. Our results showed that human liver CYP450 was involved in the oxidation of dihydropyridine ring of nimodipine.