Determination of polythiazide and prazosin in human plasma by high-performance liquid chromatography.

A selective high-performance liquid chromatographic method has been developed for the determination of polythiazide in human plasma down to concentrations of 0.5 ng/ml. Polythiazide and an internal standard (epithiazide) are simultaneously extracted from the sample, the extract is purified on a silica micro-column and analyzed on a muBondapak CN column. Chloroform-methanol (97:3) is the eluent, with spectrophotometric detection at 264 nm. The extraction methodology developed for the analysis of polythiazide in blood plasma allows the simultaneous quantitative determination of prazosin, which is frequently administered together with thiazide diuretics. The precision and accuracy of both the polythiazide and the prazosin assays are excellent and are not seriously affected by the simultaneous presence of both drugs in the plasma. Therefore, determination of polythiazide and prazosin is possible using a single plasma sample.