Crotalidae polyvalent immune Fab (ovine) dosing in Agkistrodon contortrix envenomation: a single-center retrospective cohort study.

Introduction: Crotalidae polyvalent immune Fab (ovine) is indicated for the treatment of Agkistrodon contortrix (copperhead) envenomation. Medical toxicologists have used lower Crotalidae polyvalent immune Fab (ovine) antivenom doses than those recommended in the prescribing information for the treatment of copperhead envenomation.

Methods: We conducted a single-center retrospective chart review of patients with copperhead envenomation seen by our medical toxicology consult service between January 2001 and June 2023. Patients with dry bites, envenomation by other snakes, no antivenom treatment, treatment with non-Fab antivenom, or inaccessible data were excluded. Trained investigators abstracted data on antivenom dosing, demographics, examination findings, laboratory results, processes of care, and opioid administration from the medical record. The primary aim was to describe antivenom dosing. The secondary aim was to assess the relationship between initial antivenom dose (less than four vials versus four or more vials) and clinical outcomes.

Results: We included 143 patients. The median (IQR) initial and total antivenom doses were four vials (two-four vials) and four vials (four-six vials), respectively. Antivenom redosing occurred in 41 cases (29%). Lower initial doses of antivenom were not associated with increases in the Snakebite Severity Score, extent of soft tissue injury, total opioid dose, length of stay, or occurrence of redosing.

Discussion: Patients seen by our consult service frequently received lower doses of antivenom than those recommended in the prescribing information, without association with poor in-hospital clinical outcomes. These results are consistent with previous observational studies and, if confirmed by prospective research, may support a change in antivenom dosing strategies for copperhead envenomation that could result in substantial cost savings.

Conclusion: Our consult service frequently used lower doses of antivenom for copperhead envenomation than recommended in the prescribing information. This practice did not appear to be associated with frequent antivenom redosing, progression of soft tissue injury, higher opioid doses, or increased length of stay.