Comparative activity of cetirizine and desloratadine on histamine-induced wheal-and-flare responses during 24 hours.

BACKGROUND: Cetirizine and desloratadine are antihistamines active in the treatment of symptoms associated with seasonal allergic rhinitis and chronic urticaria. OBJECTIVE: To compare the antihistamine activity of desloratadine, the active metabolite of loratadine, with that of cetirizine in the skin wheal-and-flare responses during 24 hours. METHODS: This was a double-blind, randomized, placebo-controlled, single oral dose, crossover study. Skin reaction to histamine (100 mg/mL), administered by prick tests, was measured by the wheal and flare surface areas for 24 hours (before treatment and at 0.5, 1, 2, 3, 4, 6, 8, 10, 12, and 24 hours). Eighteen healthy volunteers (mean age, 33.9 years; 13 women) participated in this study. The areas under the curves of the wheal-and-flare responses as a function of time (primary efficacy variables) were compared using analysis of variance. RESULTS: A highly significant overall treatment effect (P < .001) was detected for wheal and flare inhibition, with the activity of cetirizine and desloratadine significantly superior to that of placebo (P < .001). In addition, the activity of cetirizine was significantly superior to that of desloratadine (P < .001). With desloratadine, only 3 of the 18 subjects achieved a wheal inhibition of at least 70%, occurring between 2 and 4 hours, whereas all subjects using cetirizine reached a wheal inhibition of at least 70% between 0.5 and 3 hours (median time, 1.7 hours). The difference between the 2 active drugs was highly significant (P < .001). The median duration of wheal inhibition of at least 70% was zero with placebo and desloratadine and was 21.9 hours with cetirizine (P < .001). No serious adverse events were reported, and no subject withdrew from the study due to an adverse event. CONCLUSION: Cetirizine was associated with significantly greater suppression of skin reactivity to histamine compared with desloratadine during 24 hours after a single dose, with a consistent duration of action for cetirizine, as previously reported.