A comparison of the effect of diphenhydramine and desloratadine on vigilance and cognitive function during treatment of ragweed-induced allergic rhinitis.

Background: Decrements in cognitive performance are associated with the use of sedating antihistamines. Most, but not all, second-generation antihistamines have been found to be nonsedating.

Objective: To examine the central nervous system (CNS) profile of a new second-generation antihistamine, desloratadine.

Methods: Subjects with ragweed-induced allergic rhinitis (aged 18-60 years) who demonstrated a predetermined severity of symptoms after priming with ragweed pollen in the Environmental Exposure Unit were randomized to receive a single dose of desloratadine, 5 mg; diphenhydramine, 50 mg; or placebo. A comprehensive battery of repeatable, automated neuropsychological tests was administered to subjects before treatment (symptomatic baseline) and 90 minutes after taking study medication.

Results: Both desloratadine (P = .04) and diphenhydramine (P < .01) alleviated the symptoms of allergic rhinitis compared with placebo, but treatment with diphenhydramine was associated with clinically meaningful decrements on all vigilance parameters (P < .05 for desloratadine-diphenhydramine contrasts). Also, subjects treated with diphenhydramine performed significantly worse than subjects given desloratadine or placebo across all cognitive domains evaluated. Most effect sizes for the mean desloratadine and diphenhydramine differences were between 0.4 and 0.8 (moderate to high). Stanford Sleepiness Scale scores also indicated significantly more somnolence with diphenhydramine vs desloratadine or placebo (P < .001). There were no significant differences on any of the cognitive parameters between subjects treated with desloratadine and those given placebo.

Conclusions: Desloratadine improved ragweed-induced allergic rhinitis symptoms without adversely affecting performance. Diphenhydramine improved allergic rhinitis symptoms but caused significant decrements in vigilance and cognitive functioning. Thus, efficacy of antihistamine treatment must be balanced against the associated effects on CNS functioning.