High Performance Liquid Chromatographic Determination of Diuretic-Antihypertensive Combination Products. I. Prazosin and Polythiazide

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Abstract
A high performance liquid chromatographic method for the simultaneous determination of prazosin and polythiazide in capsules is presented. Prazosin, polythiazide and benzo-phenone (internal standard) were separated by reverse phase chromatography on cyano-bonded phases from four manufacturers using acetonitrile-phosphate buffer mobile phases. Detection was by ultraviolet absorbance at 268 nm. Recoveries from synthetic formulations were 100.2 ± 0.7% for prazosin and 99.7 ± 0.7% for polythiazide. The method may also be used as a stability indicating assay for each drug substance and its impurities.