Efficacy of antihistamine pretreatment in the prevention of adverse reactions to Hymenoptera immunotherapy: A prospective, randomized, placebo-controlled trial

Background: Some clinical studies suggest that a combination of an H₁- and H₂-antagonist may be effective in the prophylaxis of allergic reactions. Objective: The efficacy of pretreatment with an H₁/H₂-antagonist combination, H₁-antagonist alone, or placebo in the prophylaxis of local and systemic adverse reactions to specific immunotherapy with Hymenoptera venom was compared. Methods: In a prospective, randomized, double-blind, placebo-controlled study, 121 patients with Hymenoptera venom allergy were treated with rush immunotherapy and pretreatment with one of the following: 120 mg of terfenadine plus 300 mg of ranitidine, 120 mg of terfenadine alone, or placebo. The incidence of unwanted systemic adverse and local reactions was recorded for up to 50 weeks. Results: In seven patients (6%), six in the placebo group and one in the terfenadine group, systemic side effects required cessation of therapy (p = 0.005). Subjective symptoms occurred in four patients (10%) in the terfenadine plus ranitidine group and in three patients (7%) in the terfenadine group. Regarding local reactions, significantly fewer patients treated with a combination of terfenadine and ranitidine and with terfenadine alone as compared with placebo had severe local symptoms of erythema (29%, 29%, and 49%), edema (24%, 18%, and 41%), and pruritus (13%, 11%, and 31%) at week 1 (p < 0.05). This therapeutic benefit was limited to the first 4 weeks of treatment. Treatment with a combination of terfenadine and ranitidine was not superior to treatment with terfenadine alone. Conclusions: Pretreatment with H₁-antihistamines with or without H₂-antihistamines significantly reduced local and systemic adverse reactions to immunotherapy with Hymenoptera venom and may therefore be helpful in the management of immunotherapy.