A RANDOMIZED DOUBLE-BLIND CLINICAL-TRIAL OF 2 ANTIVENOMS IN PATIENTS BITTEN BY BOTHROPS ATROX IN COLOMBIA

A randomized double-blind clinical trial in 39 patients envenomed by B othrops atrox in Antioquia and Choc6, Colombia, was performed to compa re the efficacy and safety of 2 equine-derived antivenoms prepared at Institute Clodomiro Picado, University of Costa Rica. Twenty patients received a monovalent anti-B. atrox antivenom (group A) and 19 patient s were treated with a polyvalent (Crotalinae) antivenom (group B). Bot h antivenoms were equally efficient in the neutralization of the most relevant signs of envenoming (haemorrhage and blood clotting time alte ration). Fourteen patients (36%) presented early adverse reactions to antivenoms and no significant difference between the 2 groups was obse rved. Urticaria (18%) was the most frequent early adverse reaction and there was no life-threatening anaphylactic reaction. Based on clinica l criteria and serum venom levels, estimated by an enzyme immunoassay, 15 patients were classified into 2 groups: mild and moderate/severe e nvenoming. With the antivenom doses used in this study (3, 6 and 9 via ls for mild, moderate and severe envenoming, respectively), both antiv enoms were equally efficient in clearing serum venom levels within the first hour of treatment, and the levels remained below the lower limi t of venom detection for 24 h. Antivenom concentration in serum remain ed high for up to 24 h after antivenom infusion, suggesting that an ex cess of antibody in relation to circulating antigen had been administe red.