Some over-the-counter cold and allergy remedies may cause more
driving impairment than being legally drunk, according to a new
study.
Researchers at the University of Iowa (www.uiowa.edu), Iowa
City, evaluated the driving performance of 40 people, ages 25 to
44, who had seasonal allergic rhinitis (hay fever) and were given
diphenhydramine, fexofenadine (Allegra), alcohol and placebo in
consecutive trials. (Allegra is marketed by Aventis
Pharmaceuticals, Kansas City, Mo., formerly Hoechst Marion Roussel,
which funded the study along with the National Institutes of
Health.)
Results showed the subjects' ``driving'' performance was poorest
after taking diphenhydramine -- even worse than when legally drunk.
Researchers tested subjects using the Iowa Driving Simulator
after they took the antihistamines, alcohol and placebo. Subjects
were tested on their ability to follow a lead car that changed its
speed randomly.
Subjects had more trouble steering and crossed the centerline
more frequently after alcohol and diphenhydramine use. They did
not, however, experience such impairment after taking fexofenadine.
This second-generation antihistamine does not appear to cause
impairment in driving, according to researchers, most likely
because -- unlike diphenhydramine -- it does not pass the blood-brain
barrier.
Diphenhydramine is the active ingredient in Benedryl
Allergy/Cold Tablets (Warner-Lambert) and Tylenol Allergy Sinus
NightTime (McNeil), among other products sold over-the-counter,
while fexofenadine is available only on prescription.
``First-generation antihistamines, such as diphenhydramine, are
known to affect driving performance,'' said Dr. John M. Weiler, UI
professor of internal medicine and lead author of the study.
``However, we were surprised to find that this antihistamine had
more impact on driving performance than did alcohol. In contrast,
we found that fexofenadine did not impair driving performance.''
Findings appear in the March 7 issue of Annals of Internal
Medicine.
Researchers on the project suspect that people frequently do not
avoid first generation antihistamines in situations when they may
be driving, said Weiler. ``These results suggest that people should
carefully read warning labels on all medications,'' he said. ``Even
if you do not feel drowsy after taking an antihistamine or alcohol,
you may be impaired.''
``We know that alcohol can impair driving,'' continued Weiler.
``We did not know that drowsiness correlated poorly with driving
impairment, suggesting that people could not predict that they were
impaired.''
Weiler said he hoped the study's impact will be twofold: that
people will read labels on medications and heed the warnings and
that they visit with their physicians when considering medications
to treat seasonal allergic rhinitis.
In an editorial appearing in the same issue, Sean Hennessy and
Dr. Brian L. Strom, of the University of Pennsylvania School of
Medicine (www.med.upenn.edu), Philadelphia, noted that if the
findings showed impairment under these experimental conditions, the
risks of motor vehicle crashes in real-life settings are likely
even higher. They urged people to use non-sedating antihistamines
if they will be driving. ``The newer, non-sedating antihistamines
have much smaller or even undetectable effects at recommended
doses, although impairment sometimes occurs at
higher-than-recommended doses,'' they wrote.
