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Sequential randomised and double blind trial of promethazine prophylaxis against early anaphylactic reactions to
H W Fan1, L F Marcopito, J L Cardoso
1Hospital Vital Brazil, Instituto Butantan, Avenue Vital Brazil 1500, 05503-900, São Paulo, Brazil.
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.
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