NEW YORK-- Combination therapy with H1 and H2 histamine blockers can benefit patients with acute allergic syndromes, a recent study demonstrates. [1]

"We have seen people who have not responded to H1-blocker therapy do much better when an H2 blocker was added," commented Robert Y. Lin, MD, in an interview with RESPIRATORY REVIEWS. Lin et al performed a randomized, double-blind, placebo-controlled study of 91 adults who had presented to an emergency department for treatment of acute allergic syndromes. Of these, 48 were given 50 mg of diphenhydramine plus 50 mg of ranitidine; the other 43 received 50 mg of diphenhydramine plus saline solution. All medications were administered parenterally.

The patients' symptoms included acute urticaria, angioedema, unexplained stridor, and pruritic rash. In most cases, the reaction resulted from exposure to a drug or food.

Patients were assessed at baseline and at one and two hours posttreatment. At baseline, the two groups were comparable in terms of heart rate, blood pressure, physical findings, and symptoms. For example, 29 patients in the ranitidine group and 24 patients in the placebo group had urticaria; angioedema was present in 22 and 27 patients, respectively. Posttreatment resolution of both symptoms was the primary outcome measurement.

EFFECTS OF TREATMENT

A reduction in heart rate was seen in both groups at one and two hours posttreatment, but the decrease was slightly greater in the patients who received ranitidine. There was no posttreatment difference in blood pressure between the two groups.

One hour after therapy, urticaria had cleared in 17 of the patients given ranitidine but in only five patients in the placebo group. Angioedema had resolved in seven of the patients who had received the H2 blocker but in only three of the patients given placebo.

At two hours posttreatment, only four patients in the ranitidine group still had urticaria, compared with 11 patients in the placebo group. Similarly, 11 patients given ranitidine and 14 patients given placebo still had angioedema. Both of these symptoms were absent in a significantly higher proportion of patients in the ranitidine group (70.5%) than in the placebo group (46.5%).

"An improved outcome over the course of one or two hours can be seen with combined H1 and H2 blockade in patients who present with urticaria and angioedema," concluded Dr. Lin, head of the Department of Allergy and Immunology at St. Vincent's Hospital in New York City. Dr. Lin is also a Professor of Medicine at New York Medical College in Valhalla, New York.

STUDY LIMITATIONS

A limitation of this study is that supplemental therapies, including epinephrine, bronchodilators, corticosteroids, and intravenous fluids, were administered at the discretion of the study physicians. As a result, significantly more patients in the placebo group received additional H1 blockers than did patients in the ranitidine group. Yet, Dr. Lin noted, resolution of urticaria (with or without angioedema) was still markedly less in the placebo group than in the ranitidine group.

According to Dr. Lin, this study suggests that patients treated with a combination of ranitidine and diphenhydramine have quicker resolution of urticaria. This may result in their being discharged sooner than those patients who receive diphenhydramine alone.

--Jennifer A. McConnon

Reference
1. Lin RY, Curry A, Pesola GR, et al. Improved outcomes in patients with acute allergic syndromes who are treated with combined H1 and H2 antagonists. Ann Emerg Med. 2000;36:462-468.