Cetirizine in the treatment of chronic urticaria.

The effects of oral cetirizine on spontaneous and provoked urticaria were evaluated in two studies. In a double-blind crossover trial, 30 patients with idiopathic urticaria received 10 or 20 mg of cetirizine or placebo. Cetirizine was significantly more effective than placebo in reducing the incidence of erythema, wheals, and pruritus. No serious side effects were reported. In the second study of ten patients with chronic urticaria, immediate and delayed reactions to injected autologous serum, histamine, kallikrein, and synthetic platelet-activating factor (PAF)-acether were inhibited by 10 mg of cetirizine. These results suggest that the mechanism of action of cetirizine may involve inhibition of PAF-induced influx of eosinophils.