Twenty-four hours of activity of cetirizine and fexofenadine in the skin

Background: Cetirizine and fexofenadine, the active metabolite of terfenadi ne, are powerful and well-tolerated H-1 receptor antagonists effective in t he treatment of skin and nose atopic diseases. Objective: We have compared the pharmacodynamic activity of the two antihis tamines at therapeutic dosages, cetirizine at 10 mg and fexofenadine at 120 mg and 180 mg, on histamine-induced skin reactivity during a 24-hour perio d after single intake. Methods: Twenty-six healthy volunteers participated in a randomized, double -blind, crossover, placebo-controlled study. The areas of wheal and flare i nduced by histamine (100 mg/mL) administered by prick test were measured at 0, 0.5, 1, 2, 4, 6, 8, 10, 12, and 24 hours postdose. Statistical analysis of the areas under the time-response curves was performed by a Friedman's ANOVA followed by a Wilcoxon test and Bonferroni's correction. Results: The three active treatments clearly inhibited the wheal and flare areas throughout the 24-hour period compared with placebo. Maximal inhibiti on occurred at 4 hours postdose. Between 4 and 24 hours postdose, the time course of inhibition by cetirizine differed significantly (P < 0.001) from that by fexofenadine at either dose, which did not differ from each other. At 24 hours, fexofenadine inhibited <40% of the skin reaction, whereas ceti rizine reduced 60% of the wheal. The duration of effect, considered as the time for wheal to be inhibited by at least 70%, also significantly favored cetirizine (19 hours) compared with fexofenadine (9.3 and 8.5 hours for 180 and 120 mg, respectively; P < 0.001). Consistency of activity was evaluate d by the frequency of total inhibition of the wheal (<greater than or equal to>95%). Consistency was observed in 26 of 26 participants for cetirizine, 21 of 26 for fexofenadine, 180 mg, and 10 of 26 for fexofenadine, 120 mg ( P < 0.001), suggesting better consistency for cetirizine. There was no seri ous adverse event. Conclusions: Our study clearly shows better duration of action and consiste ncy of the antihistaminic activity of cetirizine compared with fexofenadine (120 and 180 mg) in the histamine-induced skin reaction during a 24-hour p eriod.