Sequential randomised and double blind trial of promethazine prophylaxis against early anaphylactic reactions to antivenom for bothrops snake bites.

Author(s): Fan HW, Marcopito LF, Cardoso JL, Franca FO, Malaque CM, Ferrari RA, Theakston RD, Warrell DA

Affiliation(s): Hospital Vital Brazil, Instituto Butantan, Avenue Vital Brazil 1500, 05503-900, Sao Paulo, Brazil.

Publication date & source: 1999-05-29, BMJ., 318(7196):1451-2.

Publication type: Clinical Trial; Randomized Controlled Trial

OBJECTIVE: To investigate the efficacy of the H1 antihistamine promethazine against early anaphylactic reactions to antivenom. DESIGN: Sequential randomised, double blind, placebo controlled trial. SETTING: Public hospital in a venom research institute, Sao Paulo, Brazil. PARTICIPANTS: 101 patients requiring antivenom treatment after being bitten by bothrops snakes. INTERVENTION: Intramuscular injection of promethazine (25 mg for adults and 0.5/kg for children) or placebo given 15-20 min before starting intravenous infusion of antivenom. MAIN OUTCOME MEASURES: Incidence and severity of anaphylactic reactions occurring within 24 hours after antivenom. RESULTS: Reactions occurred in 12 of 49 patients treated with promethazine (24%) and in 13 of 52 given placebo (25%); most were mild or moderate. Continuous sequential analysis indicated that the study could be interrupted at the 22nd untied pair, without preference for promethazine or placebo. CONCLUSION: Prophylaxis with promethazine does not prevent early reactions. Patients should be observed carefully during antivenom infusion and the subsequent few hours.