Cimetidine treatment of recalcitrant acute allergic urticaria.

Cimetidine, an H-2-receptor-blocking antihistamine, was used in the treatment of five consecutive patients who developed acute allergic urticaria in response to insect stings. All five had persistent hives after treatment with at least epinephrine and diphenhydramine (Benadryl, an H-1 receptor blocker). All also had been given corticosteroids. Each patient responded dramatically within 15 minutes to one IV infusion of 300 mg cimetidine. All were discharged on oral cimetidine (300 mg every six hours) and reported no recurrences or exacerbations of urticaria on follow up. There were no complications. Cimetidine may be effective in patients with recalcitrant acute allergic urticaria who are already being treated with H-1-receptor-blocking antihistamines. Controlled clinical trials should be done to confirm the efficacy of cimetidine for treatment of acute allergic reactions.