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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.
    No
    Yes

    Result:

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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 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.

    Formula

    Algorithm, as follows:

    1. Are there signs of envenomation? Signs include:
      • Swelling, tenderness, redness, ecchymosis, or blebs at bite site.
      • Elevated protime, decreased fibrinogen or platelets.
      • Systemic signs (hypotension, bleeding beyond puncture site, refractory vomiting, diarrhea, angioedema, neurotoxicity).

    If YES, proceed to 2.

    If NO, this is an apparent dry bite or no bite. Observe patient ≥8 hours, repeat labs prior to discharge, and do not administer antivenom.

    1. Check for indications for antivenom:
      • Swelling that is more than minimal and is progressing.
      • Elevated protime, decreased fibrinogen or platelets.
      • Any systemic signs.

    If YES, proceed to 3.

    If NO, this is an apparent minor envenomation. Observe patient 12-24 hours, repeat labs at 4-6 hrs and prior to discharge, and do not administer antivenom.

    1. Administer antivenom:
      • Establish IV access, give IV fluids.
      • Mix 4-6 vials of crotaline Fab antivenom in 250 mL NS and infuse over 1 hour.
      • Increase dose to 6-8 vials for patients in shock or with serious active bleeding.
      • Reexamine after 1 hour, and proceed to 4.
    1. Check for control of envenomation (after initial antivenom):
      • Swelling and tenderness not progressing.
      • Protime, fibrinogen, platelets normal or clearly improving.
      • Clinically stable.
      • Neurotoxicity resolved or clearly improving.

    If YES, monitor patient and perform serial examinations and maintenance therapy (2 vials of antivenom every 6 hours x 3 doses (given 6, 12, and 18 hours after initial control). Maintenance therapy may not be needed if close observation by physician expert is available.

    If NO, then repeat antivenom until control is achieved.

    Evidence Appraisal

    Lavonas et al analyzed the medical literature regarding use of Crotalidae Polyvalent Immune Fab for pit viper envenomations. After analysis of 42 original articles, this panel of experts met and held a consensus-building meeting, which resulted in a consensus treatment algorithm.

    Dr. Eric J. Lavonas

    About the Creator

    Eric J. Lavonas, MD, is a practicing emergency physician and medical toxicologist. He is a professor of emergency medicine at the University of Colorado School of Medicine, and has served as the interim director of the emergency department at Denver Health. His research interests include envenomation and antidote development, carbon monoxide poisoning, and health care quality.

    To view Dr. Eric J. Lavonas's publications, visit PubMed

    Content Contributors
    • Stephen A. Harding, MD
    About the Creator
    Dr. Eric J. Lavonas
    Partner Content
    Content Contributors
    • Stephen A. Harding, MD