A randomized blinded clinical trial of two antivenoms, prepared by caprylic acid or ammonium sulphate fractionation of IgG, in Bothrops and Porthidium snake bites in Colombia: correlation between safety and biochemical characteristics of antivenoms

A randomized blinded clinical trial was performed in 53 patients bitten by Bothrops sp. and Porthidium sp. in Antioquia and Chocó, Colombia, in order to compare the efficacy and safety of two antivenoms made of whole IgG obtained by either ammonium sulphate (monovalent anti-B. atrox) or caprylic acid (polyvalent) fractionation. Additionally, antivenoms were compared by electrophoretic and chromatographic analyses and anticomplementary activity in vitro. With a protocol of 2, 4 and 6 antivenom vials for the treatment of mild, moderate and severe envenomings, respectively, both antivenoms were equally efficient to neutralize the most relevant signs of envenoming and to clear serum venom levels in patients from the first hour and later on. Three patients with severe envenoming and initially treated with less than six vials on admission had persistent or recurrent venom antigenemia within 12-48 h. Monovalent antivenom fractionated by ammonium sulphate precipitation had higher amounts of protein aggregates and nonimmunoglobulin proteins than polyvalent antivenom fractionated by caprylic acid precipitation. Both antivenoms presented anticomplementary activity in vitro, being higher in the monovalent product. In agreement, monovalent antivenom induced a significantly higher incidence of early antivenom reactions (52%) than polyvalent antivenom (25%).

A randomized, blinded, comparative trial of one pepsin-digested and two whole IgG antivenoms for Bothrops snake bites in Uraba, Colombia. The Regional Group on Antivenom Therapy Research (REGATHER)

The therapeutic efficacy and the incidence of early antivenom reactions (EARs) were compared in a clinical trial performed in 79 patients bitten by Bothrops sp. in Urabá, Colombia. Patients were randomized into three groups according to the antivenom administered: A (n = 30, Butantan polyspecific, pepsin-digested Bothrops antivenom); B (n = 27, Butantan polyspecific, whole IgG Bothrops antivenom); and C (n = 22, Colombian commercial, monovalent, whole IgG Bothrops antivenom). The groups were comparable in all clinical and epidemiologic aspects; 33 patients had mild, 22 moderate, and 24 severe envenoming. At the doses used (two, four, and six vials [10 ml/vial] for mild, moderate, and severe envenomings, respectively) there were no differences between the antivenoms in restoring normal hemostatic parameters within 24 hr. The evolution of local envenoming was comparable in the three groups. Serum venom/antivenom kinetics determined by ELISA showed a complete clearance of venom levels 1 hr after treatment in mild/moderate envenomings. In severe cases, venom levels remained detectable up to 24 hr and recurrence of antigenemia was observed in some cases. Antivenom concentrations remained at high levels up to 24 hr of treatment. The incidence of EARs was significantly different in the groups: A (36.7%), B (11.1.%), and C (81.8%). There were no life-threatening anaphylactic reactions. We conclude that the efficacy of the three antivenoms was similar in neutralizing human Bothrops envenomings and that the production of whole IgG antivenoms by caprylic acid fractionation is a good alternative for reducing the incidence of EARs.

A randomized double-blind clinical trial of two antivenoms in patients bitten by Bothrops atrox in Colombia. The Regional Group on Antivenom Therapy Research (REGATHER)

A randomized double-blind clinical trial in 39 patients envenomed by Bothrops atrox in Antioquia and Chocó, Colombia, was performed to compare the efficacy and safety of 2 equine-derived antivenoms prepared at Instituto Clodomiro Picado, University of Costa Rica. Twenty patients received a monovalent anti-B. atrox antivenom (group A) and 19 patients were treated with a polyvalent (Crotalinae) antivenom (group B). Both antivenoms were equally efficient in the neutralization of the most relevant signs of envenoming (haemorrhage and blood clotting time alteration). Fourteen patients (36%) presented early adverse reactions to antivenoms and no significant difference between the 2 groups was observed. Urticaria (18%) was the most frequent early adverse reaction and there was no life-threatening anaphylactic reaction. Based on clinical criteria and serum venom levels, estimated by an enzyme immunoassay, 15 patients were classified into 2 groups: mild and moderate/severe envenoming. With the antivenom doses used in this study (3, 6 and 9 vials for mild, moderate and severe envenoming, respectively), both antivenoms were equally efficient in clearing serum venom levels within the first hour of treatment, and the levels remained below the lower limit of venom detection for 24 h. Antivenom concentration in serum remained high for up to 24 h after antivenom infusion, suggesting that an excess of antibody in relation to circulating antigen had been administered.