Bioequivalence evaluation of two formulations of doxazosin tablet in healthy thai male volunteers.

The bioequivalence of two doxazosin 2 mg tablets was determined in 24 healthy Thai male volunteers after one single dose in a randomized cross-over study with a one week washout period. The study was conducted at Faculty of Pharmaceutical Sciences and Health Sciences Research Institute, Naresuan University, Phitsanulok, Thailand. Reference (Cardura, Heinrich Mack Nachf. GmbH & Co. GK, Illertissen, Germany) and test (Dozozin-2, Umeda Co., Ltd., Bangkok Thailand) were administered to volunteers after overnight fasting. Blood samples were collected at specified time intervals and plasma was separated. The validated HPLC method with fluorescence detection was used for quantification of doxazosin in plasma samples. The pharmacokinetic parameters, T(max), C(max), AUC(t), AUC(infinity), T(1/2), lambda(z), Cl and V(d), were determined from plasma concentration time profile of both formulations by using non-compartment analysis. The calculated pharmacokinetic parameters were compared statistically to evaluate bioequivalence between the two brands. The analysis of variance (ANOVA) using log-transformed C(max), AUC(t), and AUC(infinity) did not show any significant difference between two formulations. The point estimates and 90% confidence intervals for C(max), AUC(t) and AUC(infinity) were within the acceptance range (0.80-1.25), satisfying the bioequivalence criteria of the Thailand Food and Drug Administration Guidelines. These results indicate that Dozozin-2 is bioequivalent to Cardura and, thus, may be prescribed interchangeably.