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Sedating Antihistamines: Don't Drive or Use Heavy Machinery

Like alcohol, traditional sedatingantihistamines may impair driving performance. These authors compared the effects of the sedating antihistamine diphenhydramine (DPH), the non-sedating antihistamine fexofenadine (FEX), and alcohol on driving performance. This randomized, blinded, crossover study was partially funded by the maker of FEX.

Forty drivers with seasonal rhinitis received single-dose FEX (60 mg), DPH (50 mg), ethanol (blood concentration, 0.1%), or placebo 2.5 hours before a1-hour drive on a standardized driving simulator. Drivers were tested on coherence (measured as ability to match the speed of a car being followed), keeping within their lane, and response time to a car that suddenly pulled out in front. Drowsiness was also measured. Coherence was comparable with placebo and FEX. Ethanol was similar to placebo and FEX in its effects on coherence, but had a greater effecton a driver's ability to respond to a car pulling out in front. DPH had the greatest impact on coherence and caused the greatest drowsiness. Self-reported drowsiness before the drive did not predict performance.

Comment: An accompanying editorial states that non-sedating antihistamines are preferable to sedating ones for patients who drive. Yet the editorialists note several database studies that showed no correlation between sedating antihistamines and traffic accidents. Although both single-dose and database studies have limitations, the message is clear: To prevent liability, physicians should warn patients about the risks of driving after taking sedating antihistamines. Non-sedating antihistamines may cost more, but using these drugs while, for example, talking on a cell phone, only increases the danger. This warning should be extended to using machinery or working in hazardous environments.

— NH Shear

Published in Journal Watch Dermatology April 1, 2000

Citation(s):

Weiler JM et al. Effects of fexofenadine, diphenhydramine, and alcohol on driving performance. A randomized, placebo-controlled trial in the Iowa Driving Simulator. Ann Intern Med 2000 Mar 7 132 354-363.

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• Medline abstract (Free)

Hennessy S and Strom BL. Nonsedating antihistamines should be preferred over sedating antihistamines in patients who drive. Ann Intern Med 2000 Mar 7 132 405-407.

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• Medline abstract (Free)