Comparative onset of action and symptom relief with cetirizine, loratadine, or placebo in an environmental exposure unit in subjects with seasonal allergic rhinitis: confirmation of a test system

Background: The environmental exposure unit (EEU) is an instrument designed to determine onset of action of antiallergic treatment. Confirmation of test results would be useful in defining its role. Objective: This study was intended to confirm a previous study comparing cetirizine, loratadine, and placebo in the EEU using an identical protocol design (randomized, double-blind, parallel-group comparison having the same symptom scoring system, endpoints, and statistical analyses), thus demonstrating reproducibility of studies conducted in the EEU. Methods: Onset of action and symptom relief with once-daily cetirizine 10 mg, loratadine 10 mg, and placebo (n = 120 each group) were evaluated replicating a previous study design. Subjects meeting inclusion and exclusion criteria and qualifying symptom scores were randomized to 2 days' exposure (6 to 7 hours daily) with treatment. Changes in total and major symptom complex (TSC, MSC) scores based on 14 symptoms evaluated at 30-minute intervals served as primary efficacy variables. Results: Onset of action again was earlier with cetirizine (at 1 hour, P less than or equal to 0.001) versus loratadine (at 3 hours, P less than or equal to 0.01). Cetirizine produced a 25.4% least-square mean reduction in TSC scores overall versus an 11.2% decrease with loratadine (P = 0.006) and a 4.8% increase with placebo (P < 0.001); loratadine and placebo were also significantly different (P = 0.002). Similar changes were also noted in MSC scores. Cetirizine consistently reduced TSC and MSC scores after the first dose versus placebo (P 5 0.001) and at most time points versus loratadine (P less than or equal to 0.05). Adverse events were reported in 1.7% of patients in each active-treatment group and in 2.5% on placebo. Conclusions: Cetirizine acted earlier and was more effective than loratadine or placebo in reducing symptoms of seasonal allergic rhinitis in subjects undergoing a controlled pollen challenge, replicating results from an earlier, identically designed study, demonstrating reproducibility of these assessments by the EEU.