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    Antivenom Dosing Algorithm

    Doses antivenom for pit viper snakebites.
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    IMPORTANT

    This dosing tool is intended to assist with calculation, not to provide comprehensive or definitive drug information. Always double-check dosing of any drug and consult a pharmacist when necessary.

    INSTRUCTIONS

    Use only in cases of severe crotalid snake envenomation (pit vipers including rattlesnakes, cottonmouths, and copperheads) in the US. Do not use in cases of coral snake envenomation or snakes not indigenous to the US. Report all cases of suspected/confirmed envenomation to poison control (1-800-222-1222).

    When to Use
    Pearls/Pitfalls
    Why Use
    • Patients with known or suspected crotalid envenomation.
    • Not valid for snakebites to head or neck, snakebites causing rhabdomyolysis, or cases of anaphylactic/anaphylactoid reactions to venom.
    • Does not apply to envenomation by coral snakes or snakes not indigenous to the US.
    • This unified treatment algorithm was developed with the goal of quick identification and management of patients who may benefit from Crotalidae Polyvalent Immune Fab.
    • There is significant variability among envenomation patients, and this algorithm does not represent a standard of care.
    • Report all cases of suspected/confirmed envenomation to poison control (1-800-222-1222).
    • Approximately 9,000 snakebites are treated yearly in the US, with 5 of those patients dying annually. The case-fatality rate is reported at 1 death per 736 patients.
    • The algorithm specifies the manifestations of crotaline envenomation that necessitate aggressive management.
    • As antivenom is an extremely expensive resource that carries significant risk of adverse events, physicians should be aware when it is indicated, as well as other steps to take in the management of these patients.
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    Yes

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    Advice

    • Leading edge of swelling and tenderness should be marked every 15-30 minutes.
    • Elevate and immobilize extremity, treat pain aggressively with IV opioids, and update tetanus status as needed.

    Management

    Maintenance therapy:

    • 2 vials of antivenom every 6 hours x 3 doses (given 6, 12, and 18 hours after initial control).
    • May not be needed if close observation by physician expert is available.

    Follow-up planning:

    • Patient should return for worsening swelling not relieved by elevation, or abnormal bleeding (e.g. melena, gum bleeding, easy bruising).
    • If fever, rash, or muscle/joint pains occur (i.e., suggesting serum sickness), patient should return.
    • Patient should be given bleeding precautions (no contact sports, elective surgery, or dental work for 2 weeks).
    • Follow-up as needed for cases in which antivenom is not given, or copperhead bites in which antivenom is given.
    • Follow-up for repeat labs twice (2-3 days and 5-7 days after discharge), then as needed.

    Critical Actions

    • Report to poison control (1-800-222-1222) all cases of suspected/confirmed envenomation.
    • Avoid the following:
      • Cutting or suctioning wound.
      • Ice.
      • NSAIDs.
      • Prophylactic antibiotics.
      • Prophylactic fasciotomy.
      • Routine use of blood products.
      • Electrical shock therapy.
      • Steroids, unless allergic phenomena observed.
      • Tourniquets.
    Content Contributors
    • Stephen A. Harding, MD
    About the Creator
    Dr. Eric J. Lavonas
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    Content Contributors
    • Stephen A. Harding, MD