High‐performance liquid chromatographic determination of doxazosin in human plasma for bioequivalence study of controlled release doxazosin tablets

AbstractA highly sensitive high‐performance liquid chromatographic quantification method with fluorescence detection was developed and validated for the determination of doxazosin in human plasma. The developed method employed one‐step extraction of doxazosin from plasma matrix with ethyl acetate using propranolol as an internal standard. Chromatographic separation was obtained within 8.0 min using a reverse‐phase Capcell‐Pak C18 column (150 × 4.6 mm i.d., 5 µm) and the mobile phase consisted of methanol–water containing 10 mM perchloric acid and 1.8 mM sodium heptane sulfonic acid (50:50, v/v) and was set at a flow rate of 1.5 mL/min. The calibration curve constructed was linear in the range of 0.3–50.0 ng/mL. The proposed method achieved a lower limit of quantification of 0.3 ng/mL, better than the reported HPLC methods. Average recoveries of doxazosin and the internal standard from human plasma matrix were 87.0 and 85.9%, respectively. The present method was validated by evaluating the precision and accuracy for inter‐ and intraday variation in the concentration range 0.3–50 ng/mL. The precision values expressed as relative standard deviations in the inter‐ and intraday validation were 1.17–6.29 and 0.84–5.94%, respectively. This method was successfully applied to the bioequivalence study of two doxazosin controlled release tablets in healthy, male human subjects. Copyright © 2006 John Wiley & Sons, Ltd.