Comparison of Crotalidae Immune F(ab')2 (Equine) and Crotalidae Polyvalent Immune Fab (Ovine) at Establishing Control of Initial Envenomation Symptoms in Louisiana Agkistrodon Envenomations.

Introduction: Copperheads and cottonmouths are responsible for most snake envenomations in Louisiana. While the United States Food and Drug Administration has approved both Crotalidae polyvalent immune Fab (FabAV) and Crotalidae immune F(ab')₂ (Fab2AV) for Agkistrodon envenomations, data is limited comparing their efficacies for this indication.

Methods: This is a retrospective study comparing FabAV to Fab2AV in the treatment of suspected Agkistrodon envenomations in Louisiana between April 2017 and October 2024. Cases identifying rattlesnakes were excluded. The primary outcome was the need for additional antivenom doses to achieve control after the initial antivenom dose.

Results: One hundred fifty-eight patients received FabAV or Fab2AV, with 100 cases meeting inclusion criteria. Fifty-seven patients received FabAV and 43 received Fab2AV. The snake was identified as copperhead in 48 cases, cottonmouth in 23, and unidentified in 29. In the FabAV cohort, the initial number of vials ranged from four to 12 with a median dose of four vials. Nine FabAV cases (16%) required additional vials for initial control after the first dose. In the Fab2AV cohort, all patients received 10 vials initially, with 24 cases (56%) requiring additional vials for initial control after the first dose. There was a significant difference in the percentage of patients requiring additional control vials between FabAV and Fab2AV.

Conclusion: In this cohort of suspected Agkistrodon envenomations, control with initial recommended dosing was more often achieved with FabAV compared to Fab2AV (84% vs. 44%). The results suggest potential benefit to hospitals stocking FabAV in Louisiana and possibly other Agkistrodon-predominant regions.