Determination of benidipine in human plasma using liquid chromatography–tandem mass spectrometry

We developed a method for determining benidipine, a dihydropyridine analogue calcium-channel blocker, in plasma using liquid chromatography–tandem mass spectrometry (LC–MS–MS). Benidipine and benidipine-d5, an internal standard, were extracted from plasma using diethyl ether in the presence of 5 M NaOH. After drying the organic layer, the residue was reconstituted in acetonitrile and injected onto a reversed-phase C18 column. The isocratic mobile phase (acetonitrile–5 mM ammonium acetate, 90:10, v/v) was eluted at 0.2 ml/min. The ion transitions monitored in multiple reaction-monitoring mode were m/z 506–174 for benidipine and m/z 511–179 for the internal standard. The coefficient of variation of the assay precision was less than 13%, and the accuracy exceeded 92%, except at the limit of quantification, 0.05 ng/ml with 1 ml of plasma, when it was 85%. This method was used to measure the benidipine concentration in plasma from healthy subjects after a single 4-mg oral dose of benidipine. This method is a very simple, sensitive, and accurate way to determine the plasma benidipine concentration.