Affinity-purified, mixed monospecific crotalid antivenom ovine fab for the treatment of crotalid venom poisoning

Study objective: To test the efficacy and safety of a new antivenom, affinity-purified, mixed monospecific crotalid antivenom ovine Fab, in human subjects with minimal or moderate crotalid envenomation. Methods: We conducted a prospective multicenter clinical trial of 11 patients 10 years or older with progressive manifestations after mild to moderate crotalid snakebite. After giving their consent, subjects received four to eight vials of study drug and were then repeatedly examined over 48 hours and at 7 and 14 days after discharge. Each patient's clinical condition was evaluated serially with the use of a validated severity score, as well as on the basis of the investigator's assessment. Results: In all 11 subjects the antivenom was judged by the investigator to have had a beneficial response. The severity score for each patient remained the same or decreased over the first 4 hours. However, two subjects demonstrated worsened condition 12 to 15 hours after antivenom administration. In no subject did an allergic reaction develop. Conclusion: in this patient group, affinity-purified, mixed monospecific crotalid antivenom ovine Fab was associated with a halt of progressive crotalid venom poisoning. Initial safety data are promising but must be addressed further in subsequent studies.