Effects of desloratadine, diphenhydramine, and placebo on driving performance and psychomotor performance measurements

IntroductionFirst-generation antihistamines taken for relief of allergic rhinitis are sedating and pose potential risks for those driving a car or operating machinery. Desloratadine is a potent, selective, histamine H1-receptor antagonist that does not easily cross the blood–brain barrier. It is nonsedating at therapeutic doses and should not affect driving or psychomotor performance.ObjectiveThis study compared the acute effects of desloratadine with diphenhydramine (active control) and placebo on the performance of healthy subjects evaluated with standard over-the-road driving tests (primary objective). The subjects’ performances were also evaluated (secondary objective) with the use of conventional performance tests.MethodsEighteen men and women received a single dose of desloratadine 5 mg, diphenhydramine 50 mg, or placebo during each period of this randomized, double-blind, three-way, crossover study. Two hours post-dosing, subjects operated a specially instrumented vehicle in a 90-min test designed to measure their ability (1) to maintain constant speed and lateral position while following another vehicle at a constant distance and (2) to respond to brake signals. Additionally, a full battery of performance tests was administered.ResultsNo significant differences were noted between desloratadine and placebo in standard deviation of lateral position (SDLP), whereas diphenhydramine treatment significantly increased SDLP (P<0.001 for both comparisons). Brake reaction time was significantly faster following treatment with desloratadine than diphenhydramine (473.72 ms vs 541.22 ms; P<0.001) or placebo (512.06 ms; P=0.033). No differences were seen among treatments in deviation of speed or distance to the lead car. The majority of performance tests showed no significant differences among groups.ConclusionDesloratadine at a therapeutic dose does not impair driving performance.