High-performance liquid chromatographic assay of prazosin for transdermal screening studies

A stability-indicating reversed phase high-performance liquid chromatographic assay for prazosin was developed to investigate the feasibility of a transdermal dosage form. The assay enabled detection of drug concentrations down to 0.05 microgram/ml and the quantification of the drug in both permeation fluids and in extracts of samples of human cadaver skin. Baseline separation of prazosin from the internal standard verapamil was attained with a cyano column. The calibration curve was linear in the range of 0.5-7 and 1-10 micrograms/ml for permeation fluids and extracts of samples of human skin, respectively. The within-day and between-day variations in the slopes of the calibration curves for diffusate and skin extract samples were low. The assay was stable even under extreme conditions of acid and base degradation. The extraction efficiency for prazosin from human skin was high. The usefulness of the assay in transdermal studies of prazosin is demonstrated.