Cetirizine therapy for seasonal allergic rhinitis: alternative dosage schedules.

A double-blind, placebo-controlled clinical trial was undertaken for two weeks to evaluate three dosing schedules for administration of cetirizine in patients with seasonal allergic rhinitis. Average severity scores from the patients' ratings for sneezing and nasal itching were significantly reduced in all three cetirizine groups (10 mg QAM or QHS and 5 mg BID), compared with placebo. The effectiveness of cetirizine in once-daily dosing schedules indicates that significant antihistaminic activity is delivered over a full 24 hours. The possibility for flexibility in dosing combined with its relatively short half-life and low incidence of adverse effects make cetirizine an important second-generation H1-antihistamine for the management of seasonal allergic rhinitis.