The efficacy of cetirizine dihydrochloride, a new H1-antagonist with minimal sedative or anticholinergic side effects was evaluated in 30 patients with chronic idiopathic urticaria. In the first part of the study, cetirizine 10 mg and placebo were compared in a double-blind cross-over trial. In the second part, patients who did not respond adequately in the first part were randomized, still double-blind, to receive 10 mg cetirizine either once daily or twice daily.

In the first part, treatment was discontinued by 17 patients on placebo and two patients on cetirizine because of lack of efficacy. Cetirizine dihydrochloride was found significantly to reduce occurrence of weals, erythema and pruritus compared with placebo (P <0.001). Twenty-six of the patients improved on cetirizine and two on placebo. Mild sedation was noted by two patients on cetirizine and by one on placebo.