A Novel Equine F[abʹ]2 Veterinary Antivenom for North American Viperid Snake Envenomation Demonstrates Efficacy by Rapid Serum Venom Removal and Improvement in Snakebite Severity Score

Abstract

Objective: To assess the efficacy of a new equine F[abʹ]2 antivenom (US Department of Agriculture code 6101.05) in removing serum venom and lowering the snakebite severity score (SSS) in animals suffering from naturally occurring viperid envenomation. Design: Retrospective study, April 2020 to October 2021. Setting: Veterinary hospitals across four North American regions. Animals: Twenty-two dogs, one cat, and one horse. Interventions: All patients received the new antivenom intravenously and were assessed for clinical response. Most dogs required one vial for clinical control of signs. Measurements and Main Results: Among the dogs and cats with detectable initial serum venom, 94.4% showed a strong response to antivenom administration, with a reduction in serum venom ranging from 94% to >99% at 2 h. Animals that experienced a 90% reduction of serum venom within 2 h greatly exceeded the 0% expected of an ineffective antivenom. The canine and feline SSS improved relative to the initial SSS at 2, 6, and 12 h in 57.9%, 77.8%, and 90.9% of cases, respectively. A favorable reduction in SSS was also appreciated in the single horse in the study. Conclusions: In the canine, feline, and equine cases of North American viperid envenomation studied, antivenom 6101.05 adequately removed serum venom and lowered the SSS.