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

Background: Allergic rhinitis affects nearly one in 10 Ammericans. Cetirizi ne is a newerer once-daily selective H-1-antagonist. In traditional clinica l trials, cetirizine has been shown to be safe and effective for the treatm ent of seasonal and perennial allergic rhinitis and chronic idiopatic urtic aria. Objective: To better characterize the efficacy and onset of action of cetirizine in a more controlled but clinically relevant setting, this agen t was compared with loratadine and placebo in patients with symptomatic sea sonal allergic rhinitis undergoing controlled pollen chalenge in an environ mental exposure unit (EEU). Methods: This was a double-blind, randomized, p arallel-group study. After screening, patients were exposed to ragweed poll en (primed) in the EEU (up to six exposures), and those with qualifying sym ptom 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 3,480 +/- 350 grains/m(3) (standard deviation), the prima ry efficacy variables were the total symptom complex (TSC) and the major sy mptom complex (MSC) scores. Symptoms were evaluated every half hour in the EEU throughout the study. Results: Cetirizine produced a 36.7% mean reducti on in TSC scores overall versus 15.4% with loratadine and 12.0% with placeb o (p less than or equal to 0.01). Cetirizine also produced a 37.4% mean red uction in MSC scores overall versus 14.7% with loratadine and 6.7% with pla cebo (p less than or equal to 0.01). Onset of action as assessed by reducti ons in TSC and RISC scores versus placebo was evident within 1 hour with ce tirizine (p less than or equal to 0.02) and 3 hours with loratadine (p less than or equal to 0.03). The incidence of treatment-related side effects wa s similar among groups, with headache reported most commonly in each group. Conclusions: Cetirizine is well tolerated and effective in reducing sympto ms of seasonal allergic rhinitis in patients undergoing controlled pollen c hallenge.