ANTIVENOM – WHEN TO GIVE, WHEN NOT TO GIVE
Antivenom is not necessary for all envenomated snake bites. CroFab® should not be given routinely on presentation, but should be reserved for those developing significant coagulopathy, systemic symptoms (CNS, GI, cardiovascular, or pulmonary), or extensive or rapidly progressing local tissue injury in the first 6-12 hours. Most envenomated bites in Missouri are copperhead bites, which are often self-limited, stabilizing and resolving with strict elevation and pain control.
Anavip® is another antivenom approved for North American rattlesnake envenomation that has resulted in significant local injury, coagulopathy, or systemic symptoms (CNS, GI, cardiovascular, or pulmonary). Anavip® offers no advantage over CroFab® for copperhead bites. Because the Anavip antibody fraction is a doublet, whereas CroFab® is single (see figure below), the half-life of Anavip® is longer. This reduces the incidence of recurrent coagulopathy in rattlesnake bites. Because copperhead bites do not produce coagulopathy in the first place, there is no advantage.
Antivenom does not reverse tissue damage that has already occurred; instead it halts or slows its progression in a severe envenomation. Fab antibody fragments work by binding and neutralizing venom toxins, facilitating redistribution away from target tissues and elimination from the body.
Contact Missouri Poison Center to receive our full snake bite management, including detailed indications and dosing for Crofab® and Anivip®.
If you have any questions about the management of snake bites, please feel free to call the Missouri Poison Center at 1-800-222-1222. Our specially trained nurses, pharmacists, and toxicologist can provide the most up-to-date information regarding exposures and treatment.