High-performance liquid chromatographic analysis of mibefradil in dog plasma and urine

The objective of the study was to develop a sensitive and specific assay for studying the pharmacokinetics of a novel calcium antagonist, a benzimidazolyl-substituted tetraline derivative, mibefradil (I) in the dog. The assay involves liquid-liquid extraction of a biological sample, reversed-phase HPLC separation and fluorescence detection (lambda ex = 270 nm and lambda em = 300 nm) of sample components. Each sample was eluted with a mobile phase pumping at a flow-rate of 2 ml/min. The mobile phase composition was a mixture of acetonitrile and aqueous solution (38:62, v/v). The aqueous solution contains 0.0393 M KH2PO4 and 0.0082 M Na-pentanesulphonic acid. The retention times were 10.7 min for I, and 12.2 min for internal standard Ro 40-6792. Calibration curves with concentrations of I ranging from 10 to 500 ng/ml were linear (r2 > 0.99). The detection limit for I was 0.5 ng/ml when 0.5 ml of plasma or urine was used. Intra- and inter-day accuracy and precision were within 10%. The assay was successfully applied to the pharmacokinetic studies of I in dogs.