Which medications in the drug class Antivenins are used in the treatment of Snakebite?

Updated: Apr 09, 2021
  • Author: Spencer Greene, MD, MS, FACEP, FACMT, FAAEM; Chief Editor: Joe Alcock, MD, MS  more...
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Available antivenin in the United States include Crotalidae Polyvalent Immune Fab Ovine (CroFab; FabAV) and Crotalidae Immune F(ab’)2 equine (Anavip; Fab2AV). Each are indicated for envenomation from American pit vipers, including rattlesnakes, copperheads, and cottonmouths (water moccasins).

Indications for antivenin use in crotalid envenomation include significant or progressive local tissue findings, hematologic laboratory abnormalities, and/or evidence of systemic toxicity (eg, airway swelling, neurological toxicity, cardiovascular collapse). The sooner antivenin is initiated, the more effective it is.

Regardless of the antivenin used, the goal is to establish “initial control”, which means any systemic illness has resolved, any hematologic laboratory abnormalities have begun to improve, and there is no further progression of the local effects. In 95% of patients, control is achieved within 1 hour following the initial dose of FabAV.

There is only one FDA-approved antivenin for native coral snake envenomations. Most hospitals do not keep NACSAV in stock, and it may be necessary to contact poison control or a regional snakebite expert for dosing instructions and to locate the antivenin or a suitable alternative.

Crotalidae polyvalent immune FAB (ovine) (CroFab)

Crotalidae polyvalent immune Fab is an affinity-purified, mixed monospecific Crotalidae antivenin indicated for the treatment of envenomation caused by North American pit vipers.

It can minimize local, hematologic, and systemic effects following copperhead, cottonmouth, and rattlesnake envenomation. Although it is most useful if started within 5.5 hours of the envenomation, it can still provide benefit even several days after the envenomation.

A randomized clinical trial of FabAV use in copperhead envenomations demonstrated that even mild bites recover faster when treated with antivenin.

Crotalidae immune FAB (equine) (Anavip)

Crotalidae Immune F(ab’)2 Equine is an equine-derived F(ab’)2AV that is indicated for the treatment of envenomation caused by North American pit vipers.

A randomized clinical trial demonstrated that F(ab’)2AV can reduce the risk of subacute coagulopathy and bleeding following treatment of envenomation.

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