Determination of cilnidipine and its metabolite in human liver microsomes by HPLC and its metabolizing kinetics

AIM: A HPLC method for the determination of cilnidipine and its major metabolite was developed and the kinetics of its metabolism in human liver microsomes was studied. METHODS: Chromatography was performed on an Hypersil BDS C₁₈ column. An acetonitril-methanol-water containing 0.01 mol/L tetrabutyl ammonium bromide (55:5:40, V/V/V) 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, V/V). RESULTS: The recovery of cilnidipine and its major metabolite for the proposed method was more than 90%. The relative standard deviations for within-day and between-day were 4.70%-8.35% for cilnidipine, and 3.88%-8.11% for its major metabolite. The calibration curve was linear in the range from 0.77 μg/ml to 98.24 μg/ml with τ = 0.999 for cilnidipine and from 0.13 μg/ml to 5.36 μg/ml with τ = 0.999 for its major metabolite. The elimination of cilnidipine and the formation of the metabolite was linear. CONCLUSION: Cilnidipine was rapidly metabolized in human liver microsomes and three metabolites of cilnidipine were isolated. The results suggested that CYP450 was involved in the metabolism of cilnidipine.