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Ann Emerg Med. 2000 Nov;36(5):462-8.

Improved outcomes in patients with acute allergic syndromes who are treated with combined H1 and H2 antagonists.

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Department of Emergency Medicine, Saint Vincents Hospital & Medical Center of New York and New York Medical College, New York, NY 10011, USA.



Although the addition of H(2) blockers to H(1) antagonists has been promoted for use in anaphylaxis, there have been no large studies establishing the advantage of this approach in treating acute allergic syndromes. In this study we tested the hypothesis that combined H(1) and H(2) blockage results in improved outcomes in patients treated for acute allergic syndromes compared with treatment with H(1) blockade alone.


In a randomized, double-blind, placebo-controlled trial, 91 adult patients with acute allergic syndromes were treated with either 50 mg of diphenhydramine and saline solution (control group) or with 50 mg of diphenhydramine and 50 mg of ranitidine (active group). These patients were treated with parenteral administration. Patients were recruited from an emergency department at an urban academic medical center. The primary endpoints were resolution of urticaria, angioedema, or erythema at 2 hours after protocol treatment. Areas of cutaneous involvement, heart rates, blood pressures, respiratory findings, and symptom scores were also assessed at baseline, 1 hour, and 2 hours.


There were significantly more patients without urticaria at 2 hours among the patients in the active group compared with those in the control group. Both groups had similar proportions of urticaria at baseline. Logistic regression models to predict resolution of urticaria, which accounted for baseline urticarial involvement, showed odds ratios in favor of the active group treatment. Similar findings were observed when the absence of both urticaria and angioedema was considered as the dependent variable. There was not a significant difference between the 2 groups with regard to the absence of erythema or angioedema (irrespective of the presence of urticaria) at 2 hours. Blood pressure and symptoms did not show differences between the 2 groups over time. Lower heart rates were observed 1 hour after treatment in the active treatment group (mean reduction 10 beats/min) compared with those found in the placebo group (mean reduction 6 beats/min).


These data show that adding H(2) blockers to H(1) antagonists results in additional improvement of certain cutaneous outcomes for patients presenting with acute allergic syndromes. These findings favor the recommendation for using combined H(1) and H(2) antihistamines in acute allergic syndromes.

[Indexed for MEDLINE]

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