A SIMPLE HPLC METHOD WITH SPECTROPHOTOMETRIC DETECTION FOR THE SIMULTANEOUS ASSAY OF NIFEDIPINE AND VERAPAMIL IN RAT PLASMA

Abstract

A simple, specific, and accurate HPLC assay method is presented for the simultaneous measurement of the calcium antagonists nifedipine and verapamil in rat plasma. The plasma sample was deproteinized by treatment with an equivalent volume of an internal standard solution (nicardipine hydrochloride in acetonitrile containing 0.1% of perchloric acid), followed by brief centrifugation. A 50 μL aliquot of the clear supernatant was analyzed on a Microsorb-MV C18, 5 μm, column using a mixture of acetonitrile-methanol-0.01 M phosphate buffer pH 5.2 (55:15:30) as the mobile phase. At a flow rate of 1 mL/min and detection at 235 nm, nifedipine, verapamil, and nicardipine were observed to elute at about 3.4 min, 6.4 min, and 9.8 min, respectively. Detector responses were linearly related to concentrations of nifedipine in the range 0.2–1 μg/mL, and of verapamil between 0.4–2 μg/mL. As little as 0.05 μg/mL of nifedipine and 0.08 μg/mL of verapamil were accurately measured by the proposed method. Mean drug recoveries from rat plasma samples spiked with 0.25–1 μg/mL of nifedipine and 0.5–2 μg/mL of verapamil was in all cases >95% (range 97.9–98.3%, n = 5, for nifedipine; 95.7–97.1%, n = 5, for verapamil). The method was found to be well suited for assessing the plasma pharmacokinetics of the title drugs following their oral and intraperitoneal coadministration to rats.

Acknowledgments