The bioavailability of two tablet formulations of cetirizine (Zetir from Abbott and Zyrtek from UCB) were compared in 14 healthy male volunteers who received a single dose of 10 mg of cetirizine dihydrochloride in an open randomized two-period crossover design with a 7-day washout period between doses. Plasma samples were obtained over a 24 h interval and cetirizine concentrations were determined by HPLC with ultraviolet detection. From the plasma cetirizine concentration vs. time curves, AUC(0-24) (area under the concentration vs. time curves from 0 to 24 h), Cmax (maximum achieved concentration), Tmax (time to achieve Cmax), Ke (terminal first order elimination constant), elimination half-life (t1/2) and AUC(0-infinity) (area under the concentration vs. time curves extrapolated to infinity) were obtained. The two cetirizine dihydrochloride tablet brands did not show statistically significant differences in bioavailability as assessed by analysis of AUC(0-24), AUC(0-infinity), Cmax, Tmax, Ke and t1/2 values. Based on these results and on the U.S. Food and Drug Administration requirements [1985, 1993], we conclude that both formulations are bioequivalent.3327-31