"Diphenhydramine Has Decongestant Effect for Seasonal Allergies: Presented at ACAAI"
By Crystal Phend
ANAHEIM, CA -- November 23, 2005 -- The antihistamine diphenhydramine (Benadryl) appears to be as effective for nasal congestion as oral decongestant medication and superior to desloratadine (Clarinex) for nasal symptoms of seasonal allergic rhinitis.
The findings were presented here on November 7[th at the annual meeting of the American College of Allergy, Asthma and Immunology (ACAAI).
This was "quite a departure from what was seen in other studies for nasal congestion," said presenter Gordon D. Raphael, MD, Clinical Investigator and Physician in private practice, Bethesda, Maryland, United States. "Perhaps this observation has been overlooked in the past."
Dr. Raphael and colleagues found significant improvements in nasal symptoms from high dose diphenhydramine compared to a standard dose of desloratadine.
However, drowsiness was much worse in the diphenhydramine group, as the researchers expected.
In the double-blind, double-dummy study, 610 patients with moderate to severe seasonal allergic rhinitis were randomized to receive 50 mg of diphenhydramine three times daily, desloratadine at a dose of 5 mg once daily, or placebo.
Although the study was criticized at the presentation for such dissimilar dosing, Dr. Raphael said dosing was based on what has been used in previous studies.
Traditional subjective scoring was used to measure 24-hour total nasal symptom score, the total symptoms score and individual symptom scores. The 1-week study occurred during the fall 2002 ragweed season.
Total nasal symptom scores, the primary endpoint, were significantly improved from baseline for patients treated with high dose diphenhydramine compared to desloratadine and placebo.
Symptoms decreased by 5.96 points in the diphenhydramine group compared to 3.88 in the desloratadine group and 3.22 for placebo. Desloratadine did not significantly improve total symptoms compared to placebo.
Individual scores for eye and nose symptoms, including nasal congestion, were all clinically and statistically reduced in the diphenhydramine group compared to desloratadine and placebo.
The most frequent adverse event was drowsiness, which is a well-known effect of diphenhydramine, particularly at the high doses used, and compared to non-drowsy desloratadine. Dr. Raphael reported that drowsiness was reported by 22.1% of diphenhydramine subjects, 4.5% of desloratadine subjects, and 3.4% of the placebo group.
Dry mouth was also more common with diphenhydramine, seen in 4.9% of patients, compared to 1.5% for desloratadine and 4.0% for placebo. Fatigue was reported by similar proportions of patients in each group.
Dr. Raphael noted that the decongestant effect seen with diphenhydramine is exciting because few oral decongestants are available and Sudafed is increasingly put behind the counter because of concerns about methamphetamine abuse.
"The superior relief that diphenhydramine offers for treating all rhinitis in addition to its ability to control nasal congestion without a separate decongestant should strongly be considered by physicians," Dr. Raphael concluded.
Warner-Lambert, now a division of Pfizer, provided funding for the study.
[Presentation title: Diphenhydramine Hydrochloride, 50 mg, Exhibits Superior Efficacy to Desloratadine, 5 mg, and Placebo in Patients with Moderate-to-Severe Seasonal Allergic Rhinitis. Abstract 60]
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