First clinical experiences with a new ovine Fab Echis ocellatus snake bite antivenom in Nigeria: randomized comparative trial with Institute Pasteur Serum (Ipser) Africa antivenom.
Meyer WP., Habib AG., Onayade AA., Yakubu A., Smith DC., Nasidi A., Daudu IJ., Warrell DA., Theakston RD.
During the past decade, effective snake antivenoms have become scarce in northern Nigeria. As a result, many patients severely envenomed by the saw-scaled or carpet viper (Echis ocellatus), which is responsible for more than 95% of the snake bites in the region, did not receive effective treatment and mortality and morbidity increased. To combat this crisis, a new monospecific ovine Fab antivenom (EchiTab) is being developed. Its theoretical advantages over conventional equine F(ab')2 antivenom are a more rapid tissue penetration and larger apparent volume of distribution (the volume of [tissue] fluid in which the the antivenom would be uniformly distributed to achieve the observed plasma concentration). In a preliminary study, two vials (20 ml; 1.0 g of protein) of EchiTab rapidly and permanently restored blood coagulability and cleared venom antigenemia in seven envenomed patients. Four experienced early reactions that responded to epinephrine. In a randomized comparative trial of one vial (10 ml; 0.5 g protein) of EchiTab or four ampules (40 ml; 2.12 g of protein) of Institute Pasteur Serum (Ipser) Africa polyspecific F(ab')2 antivenom, there were fewer reactions, but only 36% and 35% of patients, respectively, showed permanent restoration of coagulability, with the remainder requiring further doses. This suggests that 0.5 g (one vial) of EchiTab is approximately equivalent to 2.12 g (four ampules) of Ipser Africa antivenom, and that a higher initial dose will be required for most patients. Measurements of circulating venom and antivenom levels reflected the clinical events.