Sequential randomised and double blind trial of promethazine prophylaxis against early anaphylactic reactions to antivenom for bothrops snake bitesBMJ 1999; 318 doi: https://doi.org/10.1136/bmj.318.7196.1451 (Published 29 May 1999) Cite this as: BMJ 1999;318:1451
- Hui Wen Fan, doctor ()a,
- Luiz F Marcopito, associate professorb,
- João Luiz C Cardoso, doctora,
- Francisco O S França, doctora,
- Ceila M S Malaque, doctora,
- Ronnei A Ferrari, doctora,
- Robert David G Theakston, associate professorc,
- David A Warrell, associate professord
- a Hospital Vital Brazil, Instituto Butantan, Avenue Vital Brazil 1500, 05503-900, São Paulo, Brazil
- b Division of Epidemiology, Escola Paulista de Medicina, Unifesp, 04039-032, São Paulo, Brazil
- c Alistair Reid Venom Research Unit, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool L3 5QA
- d Centre for Tropical Medicine, University of Oxford, John Radcliffe Hospital, Headington, Oxford OX3 9DU
- Correspondence to: Dr H W Fan
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, São 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.
Antivenom therapy may cause early anaphylactic reactions
Various drugs are used to prevent reactions, but none have been tested in randomised controlled studies
This study showed that promethazine is not better than placebo at preventing early reactions
Although most reactions are mild or moderate, trials of other drugs should be done to reduce frequency of anaphylaxis
Funding Promethazine and placebo were donated by Rhodia Farma Ltd. The study was supported by the science and Technology for Development Programme of the European Community (Contract No Ts3-CT91-0024).
Competing interests None declared.