Clinical safety of a polyvalent F(ab′) 2 equine antivenom in 223 African snake envenomations: a field trial in Cameroon

Abstract

A large-scale clinical trial was conducted, according to World Health Organization Good Clinical Practice guidelines, in 7 centres in north Cameroon to determine the safety and efficacy of a polyvalent antivenom composed of purified F(ab′) 2-This study included 223 patients presenting clinically with obvious snake bite, predominantly due to Echis ocellatus (viper), the most abundant species in this savannah region. Clinical surveillance was maintained for 5 d in all patients and until the twenty-sixth day in 74% of cases. Two 10 mL ampoules of polyvalent F(ab′) 2 equine antivenom (Ipser Africa ™) were administered to each patient by intravenous infusion. If necessary, treatment was repeated 1 h after the end of the first infusion, and then with a frequency determined by the patient's clinical condition. Before initiation of antivenom treatment, the main clinical disorders observed on admission were oedema (93·7%) and haemorrhage (48·9%), with a clotting time longer than 30 min in 65·4% of patients. Clinical cure was obtained in 213 patients (96·8%). No amputation was necessary, and the case fatality rate was only 1·3%. On average, 4·6 (±3·7) ampoules were administered per patient; 43% of subjects recovered after only a single infusion of 2 ampoules. Early adverse reactions, of varying degrees of severity, were observed in 6·3% of patients. A severe early reaction, anaphylactic shock, was observed in only one patient (0·4%). Serum sickness was observed in another patient. Polyvalent F(ab′) 2 equine antivenom given by repeated 20 mL intravenous infusions is a safe and effective treatment for envenomation caused by African vipers.