Internally standardized simultaneous assay of gallopamil enantiomers in human plasma by means of high performance liquid chromatography.

A high performance liquid chromatographic method with internal analogue standardisation for the simultaneous assay of the gallopamil enantiomers in human plasma after administration of racemic gallopamil is described. The method comprises extraction from alkalinized plasma into an n-hexane/2-propanol phase (95:5), back extraction into 1 N hydrochloric acid and extraction into n-hexane/ 2-propanol (95:5) after addition of 5 N sodium hydroxide. Separation of the optical antipodes was achieved by the use of a chiral phase (Daicel Chiralcel OD-H) and quantification by means of fluorescence detection. A limit of detection of about 0.2 ng/ml was determined for both enantiomers. Under routine conditions the limit of determination (variation coefficient < 20%) was about 0.5 ng/ml for (R)- and (S)-gallopamil. The method is not impaired by the known metabolites. The suitability of the method for clinical pharmacology studies is demonstrated with samples obtained from healthy subjects. First results of kinetic studies in humans showed that the (R)-enantiomer dominates after oral administration of racemic gallopamil.