Snakebite Medication

Updated: May 08, 2020
  • Author: Spencer Greene, MD, MS, FACEP, FACMT, FAAEM; Chief Editor: Joe Alcock, MD, MS  more...
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Medication Summary

The goals of pharmacotherapy in the treatment of snakebite are to alleviate pain, prevent paralysis, minimize tissue damage, correct hematologic toxicity, and maintain adequate perfusion.



Class Summary

The specific treatment for snake envenomations is antivenom. There are currently several antivenoms on the US market. Crotalidae Polyvalent Immune Fab Ovine (CroFab®, henceforth FabAV) has been commercially available since 2000. It is FDA-approved for the treatment of all North American crotalid envenomations.

Crotalidae Immune F(ab’)2 Equine (Anavip®, henceforth Fab2AV) has been used in Mexico since 1984 and has been available in the United States since 2018. At the time of this writing, it is FDA-approved for the treatment of North American rattlesnake, but not copperhead or cottonmouth, envenomations.

Indications for antivenom 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 antivenom is initiated, the more effective it is.

The typical initial dose of FabAV is typically 4-6 vials, although severe envenomations may warrant 8-12 vials immediately. Ten vials are given initially when using Fab2AV. Dosing should not be adjusted for pediatric patients.

Regardless of the antivenom 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.

If control is not achieved using FabAV, an additional 4-6 vials should be administered. If using Fab2AV, another 10 vials should be given. It is prudent to contact your regional poison control center or snakebite expert in these complicated cases.

If FabAV is being used, once initial control is established, maintenance dosing, consisting of 2 vials every 6 hours for three doses should be started 6 hours after control is achieved. Maintenance has proven to decrease recurrence of both local effects and hematologic toxicity. If at any point the patient worsens clinically, a larger dose should be given.

Maintenance is not typically recommended for Fab2AV.

There is only one FDA-approved antivenom 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 antivenom or a suitable alternative.

Crotalidae polyvalent immune FAB (ovine) (Copperhead Antivenom (Immune FAB), Cottonmouth Antivenom (Immune FAB), CroFab)

Crotalidae polyvalent immune Fab is an affinity-purified, mixed monospecific Crotalidae antivenom. It is FDA-approved for the treatment of all North American crotalid envenomations.

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 antivenom.

Initial dosing is 4-12 vials and should be determined by the severity of local findings rather than the suspected species responsible for the bite.

Crotalidae immune FAB (equine) (Anavip)

Crotalidae Immune F(ab’)2 Equine is an equine-derived F(ab’)2AV that is FDA-approved for the treatment of North American rattlesnake envenomations.

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



Class Summary

Infections following snakebite are exceptionally uncommon. Prophylactic antibiotics are not recommended. They do not improve outcomes, and indiscriminate antibiotic use leads to adverse effects, antibiotic resistance, and unnecessary costs.

Antibiotics should only be administered if there is clinical evidence of an infection. The choice of oral versus parenteral antibiotic should be based on the patient’s overall condition, but coverage should be broad.



Class Summary

Snakes do not harbor Clostridium tetani in their mouths, and the risk of acquiring tetanus following snake envenomation is exceptionally low. That said, if a patient's tetanus immunization is not current, a TDaP should be administered while the patient is being evaluated. However, tetanus immunoglobulin in unnecessary.

Diphtheria-tetanus toxoid (Decavac)

Diphtheria-tetanus toxoid is used to induce active immunity against tetanus in selected patients. The immunizing agents of choice for most adults and children older than 7 years are tetanus and diphtheria toxoids. It is necessary to administer booster doses to maintain tetanus immunity throughout life.

Pregnant patients should receive only tetanus toxoid, not a product containing the diphtheria antigen.

In children and adults, one may administer into the deltoid or midlateral thigh muscles. In infants, the preferred site of administration is the mid thigh laterally.


Cholinesterase inhibitors, peripheral

Class Summary

Anticholinesterase inhibitors interfere with the degradation of acetylcholine by acetylcholinesterase, thereby increasing the amount of acetylcholine available at the neuromuscular junction and increasing the chance of activating the acetylcholine receptors.

Neostigmine (Bloxiverz, Prostigmin)

Neostigmine is a peripherally acting inhibitor of acetylcholinesterase. It allows acetylcholine concentrations at the neuromuscular junction to rise and overcome any postsynaptic blockade by the alpha-toxins that may be present in coral snake venom.