High-performance liquid chromatographic method for quantitative determination of amlodipine in human plasma and pharmaceutical dosage form and its application to pharmacokinetic studies.

An accurate, sensitive, and reproducible high-performance liquid chromatographic method for the quantitation of amlodipine besylate in human plasma has been developed and validated. The drug, internal standard, and major metabolite were eluted from a C(18) hypersil HyPurity column (3 microm, 3.9 mm i.d. x 150 mm) at room temperature with a mobile phase consisting of acetonitrile-potassium dihydrogen phosphate buffer (0.05 M) and acetic acid (62:38:0.1) with the pH adjusted to 3.5 using phosphoric acid. The flow-rate was 1.8 mL/min. The limit of detection was 1.0 ng/mL, and the limit of quantification of amlodipine besylate in plasma was 10 ng/mL. The intra- and inter-day precisions showed coefficients of variation ranging from 5.98-11.4% and from 5.60-11.74%, respectively at three different levels of concentration. The averages of the absolute and relative recoveries were found to be 96.74-98.51% and 95.96-100.71%, respectively. Stability studies showed that amlodipine besylate is stable for at least 2 months in plasma after freezing at -20 degrees C. The method was successfully applied for a pharmacokinetic study and for the determination of commercial amlodipine tablet content.