Cetirizine, loratadine, or placebo in subjects with seasonal allergic rhinitis: effects after controlled ragweed pollen challenge in an environmental exposure unit.

BACKGROUND: Allergic rhinitis affects nearly one in 10 Americans. Cetirizine is a newer once-daily selective H1-antagonist. In traditional clinical trials, cetirizine has been shown to be safe and effective for the treatment of seasonal and perennial allergic rhinitis and chronic idiopathic urticaria.

OBJECTIVE: To better characterize the efficacy and onset of action of cetirizine in a more controlled but clinically relevant setting, this agent was compared with loratadine and placebo in patients with symptomatic seasonal allergic rhinitis undergoing controlled pollen challenge in an environmental exposure unit (EEU).

METHODS: This was a double-blind, randomized, parallel-group study. After screening, patients were exposed to ragweed pollen (primed) in the EEU (up to six exposures), and those with qualifying symptom scores were randomized to controlled pollen exposure (two periods of 5.5 to 6.5 hours over 2 days) and once-daily treatment with 10 mg cetirizine (n = 67), 10 mg loratadine (n = 67), or placebo (n = 68). The mean ragweed pollen level was 3480 +/- 350 grains/m3 (standard deviation). The primary efficacy variables were the total symptom complex (TSC) and the major symptom complex (MSC) scores. Symptoms were evaluated every half hour in the EEU throughout the study.

RESULTS: Cetirizine produced a 36.7% mean reduction in TSC scores overall versus 15.4% with loratadine and 12.0% with placebo (p < or = 0.01). Cetirizine also produced a 37.4% mean reduction in MSC scores overall versus 14.7% with loratadine and 6.7% with placebo (p < or = 0.01). Onset of action as assessed by reductions in TSC and MSC scores versus placebo was evident within 1 hour with cetirizine (p < or = 0.02) and 3 hours with loratadine (p < or = 0.03). The incidence of treatment-related side effects was similar among groups, with headache reported most commonly in each group.

CONCLUSION: Cetirizine is well tolerated and effective in reducing symptoms of seasonal allergic rhinitis in patients undergoing controlled pollen challenge.