Abstract

A high performance liquid chromatographic method was developed for the estimation of doxazosin in human plasma. It employs a simple and rapid method of sample preparation. Doxazosin and an internal standard (prazosin) were chromatographed as ion pairs with heptane sulphonic acid. Sample preparation involved liquid-liquid extraction with diethyl ether, evaporation of the organic layer, reconstitution of the residue into mobile phase and injection of 20 µl into the chromatograph. Chromatography was performed using ODS C18, 5µ reverse-phase column with fluorescence detection. Mobile phase consisted of heptane sulphonic acid buffer and methanol, At a flow rate of 1.2 ml/min, one analysis was completed in less than 10 min. The method was sensitive and reproducible with accurate detection as low as 0.1 ng/ml in plasma.The method was linear for doxazosin concentrations in the range of 0.5-30 ng/ml (r2=0.9976). Recoveries for the same drug concentrations from spiked human plasma ranged from 90-95% (n=5). The mean RSD values for interday and intraday assay reproducibility (n=5) were 4.47% and 4.52% respectively. Peak area ratios were fit to a least squares linear regression algorithm with a 2/x weighting. LOD and LOQ of the method were found to be 0.1 ng/ml and 0.5 ng/ml, respectively.