Parallel infusion of hydrocortisone +/- chlorpheniramine bolus injection to prevent acute adverse reactions to antivenom for snakebites.

OBJECTIVE To investigate the efficacy of continuous infusion of hydrocortisone with or without chlorpheniramine bolus against early adverse reactions to polyspecific antivenom. DESIGN AND SETTING Prospective, double-blind, randomised, placebo-controlled trial at General Hospital, Anuradhapura, Sri Lanka. SUBJECTS 52 patients with snake envenoming were randomised to receive infusion of hydrocortisone (Group A), hydrocortisone with chlorpheniramine bolus (Group B) or placebo (Group C) during the administration of antivenom. INTERVENTION Hydrocortisone 1000 mg in 300 mL of normal saline infusion was started 5 min before and continued for 30 min after antivenom. Chlorpheniramine 10 mg intravenous bolus dose was given 5 min after commencement of antivenom. MAIN OUTCOME MEASURES Occurrence and severity of adverse reactions to antivenom. RESULTS Adverse reactions were observed in 80% (12/15) of Group A, 52% (11/21) of Group B, and 81% (13/16) of Group C. Reactions were mild or moderate except in two patients. A significant reduction in the number of adverse reactions was seen in Group B compared with the placebo group (difference, 29 percentage points; 95% CI, 0.2 to 58 percentage points). There was no significant difference between Group A and the placebo group. CONCLUSION Prophylaxis with a parallel hydrocortisone infusion alone is ineffective in reducing the occurrence of acute adverse reaction to antivenom serum, but combining it with chlorpheniramine seems efficacious.