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September 23, 2002 — A commonly used, sedating antihistamine available over-the-counter (OTC) was found to have twice the risk of causing serious personal injury compared with a non-sedating antihistamine in a new study published in Annals of Allergy, Asthma & Immunology, the scientific journal of the American College of Allergy, Asthma & Immunology (ACAAI).
Studies indicate some 20 million Americans use OTC antihistamines for seasonal and perennial allergic rhinitis, which affects one-sixth of the U.S. population. The top selling OTC antihistamine is Benadryl®.
"Our study compared the risk of injury — including wounds, fractures and crushing injuries — in patients initially prescribed the sedating antihistamine diphenhydramine (Benadryl) with the risk of injury in patients initially prescribed loratadine (Claritin®.), a non-sedating antihistamine," said William D. Finkle, Ph.D., Consolidated Research, Inc., Los Angeles, principal investigator of the study.
"We found that in the first month after a first prescription for Benadryl, the rate of injuries was about twice the rate during the same period after a first prescription for Claritin. Moreover, the excess injury rate was highest in the first week after the prescription and declined to the Claritin injury rate after about five weeks, which is what one would expect from a 30-day prescription," Dr. Finkle said.
According to the authors, if this association represents the actual effects of diphenhydramine, half the injuries occurring in the month after the prescription would be attributable to diphenhydramine.
"Since Benadryl is a frequently used drug, the possibility that its use increases the risk of injury is a potentially important public health problem. The injuries studied occur often, and the patient, insurer and societal burden of these injuries is substantial. While our findings suggest that the use of Benadryl should be considered cautiously, further study of the evidence of excess risk of injury associated with Benadryl is needed," Dr. Finkle said.
"Sedation by antihistamines is governed by dose-response relationships," said guest editorial co-author Henry Milgrom, M.D., National Jewish Medical and Research Center, and the University of Colorado Health Sciences in Denver. "Drug dosage can be carefully controlled in clinical trials, and dose-response relationships can be credibly defined.
"Most studies are in agreement with Finkle et al and support the premise that classic antihistamines are more likely to cause sedation than second- (discontinued medications astemizole and terfenadine) and third-generation antihistamines (azelastine, cetirizine, desloratadine, ebastine, fexofenadine, loratadine and mizolastine). However, no antihistamine preparation is completely free of sedating effects. The newer agents given at doses higher than recommended also may produce a significant performance impairment," Dr. Milgrom said.
"We need to understand better who is prescribing diphenhydramine, given its OTC status. Finkle and colleagues rightly call for more investigation of the relation between antihistamine type and risk and for the inclusion of OTC drugs in these studies," he said.
The editorial authors note that concealed variables may be responsible for the observed results, such as how sick the patient was, whether increased activity exposed them to increased risk, or whether or not they consumed alcohol.
Close monitoring of drugs for their capacity to cause drowsiness by the FDA has led to stern warnings about operating machinery — including vehicles — while taking these drugs. However, the FDA does not require studies to examine whether a drug causes performance impairment according to John M. Weiler, M.D., who was author of a second guest editorial discussing implications of the study. Weiler and his colleagues at the University of Iowa previously reported that diphenhydramine can impair driving in a simulator as much as does alcohol.
"With publication of the report by Finkle et al, we now have some real-world data that may help to quantify the risks of taking a sedating antihistamine. Physicians and their patients should be aware of the serious associated risks and should select medications that do not have the potential to cause impairment," Dr. Weiler said.
In a recent survey conducted by the ACAAI, 94 percent of allergy sufferers said their quality of life, often including their work productivity and concentration, is affected when their allergy symptoms act up. Yet, only 50 percent of them consider the disease to be a serious medical condition and nearly two-thirds (64 percent) did not see an allergist or other doctor the last time they experienced allergy symptoms.
"With many different allergy medications available today, people mistakenly believe this disease can be diagnosed and treated without the involvement of a medical expert," said Dr. Bobby Q. Lanier, president of ACAAI. "Clearly, these findings on risk of serious injury associated with the use of sedating antihistamines illustrate the importance of allergy testing and appropriate treatment by an allergist or other physician."