, Volume 169, Issue 1, pp 84-90
Date: 30 Apr 2003

Driving ability after acute and sub-chronic administration of levocetirizine and diphenhydramine: a randomized, double-blind, placebo-controlled trial

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Sedation following antihistamine use poses a danger to ambulant patients involved in daily activities such as driving.


To investigate effects of levocetirizine (5 mg), diphenhydramine (50 mg), and placebo on driving ability during normal traffic.


Forty-eight healthy volunteers participated in a double-blind, placebo-controlled, randomized clinical trial. Treatments were administrated on days 1, 2, 3 and 4, exactly 1.5 h before the start of the standardized driving test (performed on day 1 and day 4). In the standardized driving test, subjects were instructed to drive with a steady lateral position, while maintaining a constant speed (95 km/h). Primary parameter was the standard deviation of lateral position (SDLP; cm). Statistical analyses were performed separately for day 1 and day 4, using analysis of variance and an equivalence test. Equivalence to placebo was evidenced if the 95% confidence interval lay between −2.6 cm and +2.6 cm.


SDLP after levocetirizine was equivalent to placebo on both day 1 (−0.66 cm; +1.12 cm) and day 4 (−0.37 cm; +1.28 cm). In contrast, SDLP after diphenhydramine differed significantly from placebo on both day 1 (P<0.0001) and day 4 (P<0.0003). On day 1, the 95% confidence interval of diphenhydramine (+1.85 cm; +3.63 cm) was partially above the upper equivalence limit (+2.6 cm), indicating clinically relevant driving impairment. On day 4, however, the 95% confidence interval of diphenhydramine (+0.74 cm; +2.38 cm) was contained within the acceptance range.


In contrast to diphenhydramine, driving performance was not significantly affected while using 5 mg levocetirizine once daily.