Moccasin Envenomation Treatment & Management

Updated: Aug 10, 2016
  • Author: Sean P Bush, MD, FACEP; Chief Editor: Joe Alcock, MD, MS  more...
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Prehospital Care

Do nothing to injure the patient or impede travel to the ED.

Support the airway, breathing, and circulation per advanced cardiac life support (ACLS) protocol with oxygen, monitors, large-bore intravenous lines, and fluid challenge. Minimize activity (if possible), remove jewelry or tight-fitting clothes in anticipation of swelling, and transport the patient to the ED as quickly and as safely as possible. Every 15 minutes, use a pen to mark and time the border of advancing edema.

In recent studies, no benefit was demonstrated when a negative pressure venom extraction device (eg, The Extractor from Sawyer Products) was evaluated; additional injury can result. [8, 9] Incision across fang marks is not recommended. Mouth suction is contraindicated.

Lymphatic constriction bands and pressure immobilization techniques may inhibit the spread of venom, but whether they improve outcome is not clear. These techniques may actually be deleterious for pit viper envenomation if they increase local necrosis or compartment pressure. Tourniquets are not recommended.

Maintain the limb in a neutral position.

First aid that lacks therapeutic value or is potentially more harmful than the snakebite includes electric shock, alcohol, stimulants, aspirin, ice application, and various folk and herbal remedies. [10, 11]

Cost and risk of acute adverse reactions generally preclude field use of antivenom. [10]

Attempts to capture or kill the snake are not recommended because of the risk of additional injury.

In the United States, all pit viper (rattlesnake, pygmy rattlesnake, and moccasin) envenomations are treated similarly, based on the severity of presenting signs and symptoms. Therefore, if the patient shows signs of envenomation (eg, pain, swelling), then species identification is not necessary. The exception to this rule is Mohave rattlesnakes, whose neurotoxic venom requires special consideration. However, because there is little overlap between the natural range of Mohave rattlesnakes and that of the moccasins (except for the Trans-Pecos region of Texas), this is rarely a clinical dilemma. [12, 13, 14]

If the venomousness of a particular snake is uncertain, consider taking photographs of the snake from a safe distance of at least 6 feet away using a cell phone or digital camera.


Emergency Department Care

Adequate hydration with intravenous fluids is indicated. Patients with hypotension should be resuscitated first with 2 isotonic sodium chloride solution challenges (eg, 20 mL/kg). Treat persistent shock with colloids, followed by pressors as indicated.

Managing envenomations is a dynamic process; administer additional antivenom as indicated by a worsening clinical course. When considering the use of antivenom, the risk of allergy to antivenom must be weighed against the benefits of reducing venom toxicity. See the algorithm [15] below.

Crotaline treatment algorithm. Crotaline treatment algorithm.

Inpatient Care

Patients believed to have dry bites, in which no venom effects develop, should be observed for at least 8 hours. Close follow-up and/or recheck examination is recommended.

Patients who have minimal snake envenomation may be admitted for overnight observation, or they may be discharged if signs of envenomation do not progress for at least 8 hours.

Patients whose envenomation is severe enough to require antivenom should be admitted.

Several reports in the literature have documented instances in which patients who were initially discharged with a mild envenomation returned in several hours with significant injury and required antivenom and admission. However, because the denominator (patients who go home with no progression) is not known, it is unclear whether the strategy of admitting all patients with mild envenomation is cost-effective.

Regardless of the period of observations, patients who are discharged should be instructed to return to the hospital if pain or swelling increase or if new symptoms develop. Because patients at home rarely elevate their envenomated limbs consistently, some increase in swelling is expected during the first 1-3 days after the patient goes home. If not accompanied by increasing pain or other signs/symptoms, this is not a concern.

If indicated, patients may require transfer after stabilization to a facility where antivenom can be administered.


This agent neutralizes toxins from snakebites. Only one antivenom is available: Crotalidae Polyvalent Immune Fab Ovine (CroFab). [16]

Crotaline Fab antivenom (CroFab; Crotaline immune Fab (ovine), Protherics, Nashville, TN) is a highly purified product derived from sheep hyperimmunized with the venom of 4 crotaline snakes, including Agkistrodon piscivorus. A relatively pure IgG fraction is extracted from the sheep serum and cleaved with papain to remove the antigenic Fc portion. Column affinity purification is then used to produce product consisting almost entirely of Fab fragments with specific affinity to snake venom. [17]

Antivenoms can be associated with acute and delayed allergic reactions. However, both the incidence and the severity of these reactions are low with crotaline Fab antivenom.

Urticaria has been reported in approximately 8% of patients treated with crotaline Fab antivenom; wheezing is reported in 2% and serum sickness in less than 10%. No deaths have been reported, and almost all patients have been able to complete antivenom therapy after treatment of mild allergic reactions.

Improved safety compared to historically utilized antivenoms has lead to a change in the management of moccasin envenomation. [18] However, the cost of therapy is significant, and cost-benefit analysis is not available. [19]

Significant clinical experience, including published case series, supports the role of Crotaline Fab antivenom in severe envenomations. [20]

Crotaline Fab antivenom has been formally tested in humans envenomated by cottonmouth snakes (A piscivorus).

In 2016, Crotalidae Polyvalent Immune Fab (Ovine) antivenom was shown to improve limb function at 14 days after copperhead (A contortrix) envenomation. The dosing regimen used in this placebo-controlled study was 6 vials initial treatment, repeated once if needed, followed by 2 vials given 6, 12, and 18 hours later, in accordance with FDA-approved dosing instructions. [21]

Another antivenom (Anavip, manufactured by Instituto Bioclon) has been FDA approved for rattlesnake envenomation; however, it did not receive an indication for moccasin envenomation.


Consider transfusion, in conjunction with ongoing antivenom administration, if antivenom alone does not correct severe coagulopathy or the patient has active severe bleeding. Transfusion is generally recommended for life-threatening bleeding (rare), a platelet count of less than 20,000 μL, or a hemoglobin value of less than 7 g/dL. Use transfusion as a temporizing measure only after adequate antivenom therapy because antivenom may correct coagulopathies more definitively. Coagulopathy often recurs and may persist for as long as 2 weeks after envenomation.

Platelets, fresh frozen plasma (FFP), and packed RBCs (PRBCs) are preferred initially to whole blood because they limit volume, immune, and storage complications. PRBCs have 80% less plasma, are less immunogenic, and can be stored about 40 days (vs 35 d for whole blood). PRBCs are obtained after centrifugation of whole blood. Leukocyte-poor PRBCs are used in patients who are transplant candidates/recipients or in those with prior febrile transfusion reactions. Washed or frozen PRBCs are used in individuals with hypersensitivity transfusion reactions.



In the United States, the nationwide Poison Help! number, 1-800-222-1222 will connect the caller the nearest poison control center. Certified poison centers have trained personnel to assist physicians in the management of poisonings, including snake bites, with 24-hour access to medical toxicologists for specific questions.

In addition, medical toxicologists are available to provide bedside patient care at some medical centers. Medical toxicologists have specific training and expertise in snakebite management.

The manufacturer of Crotaline Fab antivenom provides a technical assistance hotline at 1-877-SERPDRUG (877-377-3784).

Consider consulting a surgeon (eg, general, orthopedic, hand) if compartment syndrome is suspected or, in the subacute phase of illness, if debridement of clearly necrotic tissue is required.

Occupational therapy, physical therapy, physiatry (rehabilitative medicine), and/or pain management consultation may be helpful to assist patients with persistent pain, swelling, or other limitations.



Antivenom-associated complications may include immediate hypersensitivity reactions and delayed hypersensitivity reactions. [22]

Immediate hypersensitivity reactions

Anaphylaxis is a type I (immediate) hypersensitivity reaction, which may be life threatening.

Anaphylactoid reactions are histamine release stimulated by rapid infusion of medications, such as antivenom, that do not involve immune system sensitization.

Both anaphylactic and anaphylactoid reactions may be characterized by urticaria, airway swelling, wheezing, and shock. Anaphylactoid reactions are related to the rate of infusion; anaphylactic reactions are not related to rate or dose.

Urticaria occurs in approximately 8% of patients treated with crotaline Fab antivenom; more severe reactions such as wheezing and hypotension occur in approximately 2%.

Immediate hypersensitivity is treated by halting the infusion and administering antihistamines, steroids, and epinephrine as needed. If continued antivenom therapy is necessary, it is often possible to complete the antivenom infusion, after appropriate therapy, at a slower rate.

Delayed hypersensitivity reactions

Urticaria has been reported in approximately 8% of patients treated with crotaline Fab antivenom; wheezing is reported in 2%, and serum sickness in less than 10%.

Serum sickness is a type III (delayed) hypersensitivity reaction.

Serum sickness is characterized by fever, urticaria or petechial rash, lymphadenopathy, and arthritis, that may occur 5 days to 3 weeks after antivenom administration. Although serum sickness is uncomfortable, it is usually benign and self-limited.



Never handle a venomous snake, even if it is believed to be dead.

Do not reach or step into places outdoors that are not visible.

At home, remove debris in which snakes might hide (eg, log piles). Remove items, such as bird feeders, that might attract snakes—seeds that fall from bird feeders attract rodents, which attract snakes.

Heavy clothing (such as hiking boots) may retard some strikes.

Young children should be closely supervised, and older children should be educated to avoid snakes. [4]


Long-Term Monitoring

Discharge instructions should include the following:

  • Keep the envenomated extremity elevated.
  • Return immediately if swelling worsens or pain becomes severe.
  • Return immediately if any abnormal bleeding or bruising, dark tarry stools, or severe headache occurs.
  • Return for signs of wound infection, such as fever, worsening redness, or swelling immediately adjacent to the bite site, or drainage of pus. Because tenderness at the bite site, more generalized swelling, and lymphangitic streaking are common manifestations of the envenomation itself, these are less useful as signs of infection.
  • Return or follow up if a fever, itchy rash, joint pain, or swollen lymph nodes occur any time during the next few weeks.
  • Do not take nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin, ibuprofen (Motrin, Advil), or naproxen (Naprosyn, Aleve) for 2 weeks after the snakebite. Acetaminophen (Tylenol) or a prescribed pain medication can be taken.
  • Do not participate in contact sports, undergo elective surgery, or have dental work for 2 weeks after the snakebite.
  • Drink plenty of liquids. Return if urine decreases in amount or becomes cola colored.
  • Referral to a physical therapist or surgeon may be indicated.
  • Patients who developed severe coagulopathy or thrombocytopenia should have these studies rechecked in 3 days, and as needed for signs of coagulation problems (eg, bleeding gums, easy bruising).