Onset of Action, Efficacy, and Safety of a Single Dose of Fexofenadine Hydrochloride for Ragweed Allergy Using an Environmental Exposure Unit

Fexofenadine hydrochloride is the active acid metabolite of terfenadine. Fexofenadine's antiallergic properties require confirmation in a clinical setting. The purpose of this study was to characterize the time to onset of clinically important relief of symptoms of allergic rhinitis in subjects taking single doses of either 60 mg or 120 mg fexofenadine HCl, or placebo, after exposure to ragweed pollen in a controlled environment. Other objectives were to assess the efficacy and safety of single doses of fexofenadine HCl. One hundred forty-six ragweed-sensitive subjects were primed in the off-season with ragweed pollen in the environmental exposure unit. One hundred thirty-six subjects who adequately responded to priming entered a single-dose placebo phase. Placebo-responders were disqualified from the study, leaving 99 subjects with adequate symptoms to be randomized and given a single dose of either fexofenadine HCl 120 mg (33), 60 mg (33), or placebo (33) after 60 minutes of allergen exposure. Exposure continued over five hours and subjects recorded symptoms every 20 minutes. This study was of a randomized, placebo-controlled, double-blind, parallel design. Median time to onset for relaxed criteria clinically important relief was 60 minutes for both fexofenadine treatment groups, and 100 minutes for placebo ( P = .018). The proportion with relief was 82% at 60 mg, 85% at 120 mg, and 64% for placebo. Treated groups had reductions in symptom scores double that of placebo. Fexofenadine is safe and efficacious at single doses of 60 mg and 120 mg. Average time to onset was 60 minutes using controlled pollen exposure in an environmental exposure units.