HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC METHOD FOR THE DETERMINATION OF NIFEDIPINE IN PLASMA AND ITS USE IN PHARMACOKINETIC STUDIES

A simple and selective high-performance liquid chromatographic (HPLC) method for the determination of nifedipine in plasma has been developed and validated. The assay is performed after single extraction of nifedipine and diazepam (internal standard) from alkalinized plasma into ether. The drug and the internal standard were eluted from a Nova Pak C-18 column at ambient temperature with a mobile phase consisting of acetonitrile:water (48: 52%, v/v) adjusted to pH 4.0 with glacial acetic acid and at a flow rate of 1.8 ml/min. The effluent was monitored with an ultraviolet detector at 240 nm. Quantification was achieved by the measurement of the peak-height ratios and the limit of quantification for nifedipine in plasma was 5 ng/ml. The intraday coefficient of variation (CV) ranged from 2.84 to 6.77% at three different concentrations and the interday CVs varied from 3-32 to 7.17%. The relative and absolute recoveries varied from 95 to 101%. Stability tests showed that nifedipine is stable for at least 5 weeks in plasma after freezing. The method is applied for the determination of the pharmacokinetic parameters of nifedipine after administration of a 20-mg tablet (slow-release tablet) to four healthy beagle dogs. The parameters obtained are comparable to previously reported values.