Measurement of plasma verapamil levels by high-performance liquid chromatography

1. We have developed an alternative procedure for the measurement of verapamil levels in human plasma by reverse-phase high performance liquid chromatography with fluorimetric detection. 2. Prior to assay, plasma is submitted to a double extraction procedure, using first n-heptane in alkaline medium and then an acid phosphate buffer. Flecainide, a compound not related to verapamil, is used as internal standard. Mean recoveries of 70 and 63% were obtained for verapamil and flecainide, respectively. 3. The sensitivity (5 ng/ml), reproducibility (inter-assay %CV = 1.7-8.7; intra-assay %CV = 2-4) and high recovery during sample clean-up make this method useful for the quantitation of verapamil in therapeutic monitoring and pharmacokinetic studies. 4. The method is illustrated with the pharmacokinetic results obtained for 14 healthy male volunteers who received a single 240 mg dose of the commercially available tablets of Dilacoron Retard 240 mg. The mean values for the area under the curve from 0 to 24 h (AUC[0-24]), maximum achieved concentration (Cmax) and time to achieve the maximum concentration (Tmax) were 863 ng h-1 ml-1, 112 ng/ml and 4 h, respectively.