A validated method for the determination of verapamil and norverapamil in human plasma

The aim of the study was to develop a simple and sensitive analytical method to determine verapamil (V) and its metabolite norverapamil (N) in human plasma with use of an HPLC isocratic system with fluorescence detection, following fast extraction of the investigated compounds. Extraction recovery was 92.12% and 89.58% for V and N, respectively. Internal standard in HPLC was propranolol. Its recovery was 82.50% on the average. Limit of detection was 0.924 ng/ml and limit of determination was 3,080 ng/ml for V, what corresponds concentration in plasma 1.232 ng/ml. For N limit of detection was 0.030 ng/ml and limit of determination was 1.001 ng/ml what corresponds 0,4 ng/ml in plasma. Parameters of validation prove that precision of the presented method is very good. The method is fast and one chromatogram separation lasts about 8 minutes. 30-40 manual (without autosampler) analyses per day were done. It was used successfully in pharmacokinetic and bioavailability studies of verapamil administration in drug formulations alternative to tablets: buccal and flotation ones.