HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC ANALYSIS OF MIBEFRADIL IN DOGPLASMA AND URINE

The objective of the study was to develop a sensitive and specific ass ay 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 samp le, reversed-phase HPLC separation and fluorescence detection (lambda( ex) = 270 nm and lambda(em) = 300 nm) of sample components. Each sampl e was eluted with a mobile phase pumping at a flow-rate of 2 ml/min. T he mobile phase composition was a mixture of acetonitrile and aqueous solution (38:62, v/v). The aqueous solution contains 0.0393 M KH2PO4 a nd 0.0082 M Na-pentanesulphonic acid. The retention times were 10.7 mi n for I, and 12.2 min for internal standard Ro 40-6792. Calibration cu rves with concentrations of I ranging from 10 to 500 ng/ml were linear (r(2) > 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 pharmacoki netic studies of I in dogs.