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    Antivenom Dosing Algorithm

    Doses antivenom (CroFab only, not Anavip) 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 symptomatic crotalid snake envenomation (pit vipers including rattlesnakes, cottonmouths, and copperheads) in the US, for CroFab administration. Do not use in cases of coral snake envenomation or snakes not indigenous to the US. Do not use for Anavip administration, as it will result in incorrect dosing. 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 crotaline envenomation (rattlesnake, copperhead, cottonmouth).
    • Not valid for snakebites to the head or neck or with cardiovascular collapse: call Poison Control (1-800-222-1222).
    • Based on the Unified Treatment Algorithm (Lavonas 2011), which 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.
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    Next Steps
    Evidence
    Creator Insights

    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:
      • Patients who did not require antivenom: as needed.
      • Copperhead victims: as needed.
      • Cottonmouth and rattlesnake victims: repeat labs (CBC, PT, fibrinogen) 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: avoid in rattlesnake/cottonmouth victims (Pham 2018).
      • 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
    Partner Content
    Content Contributors
    • Stephen A. Harding, MD