A chiral LC-MS/MS method for the stereospecific determination of efonidipine in human plasma.

Efonidipine hydrochloride is a new generation dihydropyridine Ca(2+) channel blocker designed to inhibit both T-type and L-type Ca(2+) channels. Efonidipine possesses a chiral carbon and is clinically administered as a racemate. In the present study, an enantioselective and sensitive LC-MS/MS method of determining efonidipine enantiomers in human plasma was developed and validated to characterize the stereoselective pharmacokinetics. Plasma samples were processed by liquid-liquid extraction (LLE). Chiral separation was optimized on a CHIRALPAK(®) ID column using an isocratic mobile phase of acetonitrile/water (60:40, v/v). Detection was using MS in multiple reaction monitoring (MRM) mode, using the transitions of m/z 632.3→91.1 for efonidipine enantiomers, and m/z 493.3→117.2 for cilnidipine (internal standard). The calibration curves were linear over 0.100-20.0 ng/mL for each enantiomer. The lower limit of quantification (LLOQ) for each enantiomer was established at 0.100 ng/mL. Intra- and inter-day precisions were less than 12.1% for each enantiomer in terms of relative standard deviation (RSD), and accuracies were between -5.0% and 5.0% in terms of relative error (RE) for each enantiomer. No chiral inversion was observed during sample storage, preparation procedure and analysis. The validated method was successfully applied to a stereoselective pharmacokinetic study of efonidipine in healthy subjects after oral administration of 40 mg (20 mg × 2) efonidipine hydrochloride tablets.