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Snake Antivenom

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Snake Antivenom, Snake Anti-Venom, Snake Antivenin, Antivenin Crotalidae Polyvalent, CroFab

  • See Also
  1. Snake Bite
  2. Envenomation
  1. Unstable SnakeBite patient
  2. All eastern Coral Snake bites
  3. Clinical worsening in SnakeBite patient
    1. Progressive local swelling and Ecchymosis at bite
    2. Coagulopathy
    3. Hypotension
    4. Mental status changes
  • Efficacy
  1. Effective if given within 24 hours of bite
  2. Most beneficial if given within 4 hours of bite
  • Contraindications
  1. Positive Skin Test for Horse Serum Sensitivity
  2. Mild pit viper bite
  • Preparations
  1. Pit vipers (Rattlesnake, Cottonmouth, Copperhead)
    1. Equine-derived Snake Antivenin (horse derived)
      1. Antivenin Crotalidae Polyvalent (ACP)
    2. Ovine-derived Snake Antivenin (CroFab)
  2. Eastern coral Snake Antivenin (Micrurus fulvius)
    1. Required in all Coral Snake bite cases
  • Protocol
  1. Start reconstituting antivenin on patients ER arrival
    1. Requires 60 minutes to prepare
  2. Consider Skin Test for Horse Serum Sensitivity
    1. Controversial due to lack of efficacy
    2. Only advantage may be a medicolegal one
  3. Consider Premedication for Allergy Prevention
  4. Be prepared for Anaphylaxis
  5. Administer antivenin
    1. Depending on severity may require more than 25 vials (typically 8-12 vials for life threatening bite reactions)
      1. Dosing is per recommendations of poison control and local herpetologists
    2. Protocols vary for ACP, CroFab, and Coral antivenin
    3. Antivenin doses are the same for children and adults
    4. Give 4-6 vials in 250 ml Normal Saline over 1 hour for any of the following findings
      1. Advancing swelling (mark margins, and repeat hourly until stops advancing)
      2. Platelet Count <100
      3. Fibrinogen <100
    5. Maintenance dosing (typically 2 vials every 6 hours)
      1. Consult with poison control
      2. May not be recommended by toxicologists (despite package inserts)
    6. Monitoring
      1. See Snake Bite for monitoring
      2. Monitor labs at baseline (see above), one hour after antivenom, and then every 6 hours until stable
      3. Monitor for Anaphylaxis and anaphylactoid reactions
      4. Recheck at 48 to 72 hours for repeat CBC, Fibrinogen (for hematologic toxicity)
    7. References
      1. Swadron and Nordt in Herbert (2016) EM:Rap 16(5): 15
  6. Rattlesnake hand bites are associated with risk of hand dysfunction
    1. CroFab 6 vials (based on expert opinion)
  7. Most protocols follow antivenom with Prednisone 40-60 mg orally daily for 5 days
    1. Consult with poison control
  • Adverse Effects
  1. Serum Sickness
  2. Severe allergy or Anaphylaxis
    1. ACP: 23 to 56% Allergic Reaction rate
    2. CroFab: 14.3% Allergic Reaction and none severe
      1. Some studies quote CroFab adverse reaction rates 0.5 to 5%
  • Disadvantages
  1. CroFab is very expensive
    1. Cost to hospital is over $1,000 per vial
    2. Typical 12 vial course with hospital mark-up pricing is over $100,000
  • Resources (Antivenin sources)
  1. Arizona Poison and Drug Information Center
    1. Exotic Snake Antivenins
    2. Phone: 520-626-6016
  2. American Zoo and Aquarium Association
    1. Antivenin indexes
    2. Phone: 301-562-0777
  • References
  1. Corbett (2016) Crit Dec Emerg Med 30(10): 28
  2. Cowling and Ferreri (2019) Crit Dec Emerg Med 33(2): 17-25
  3. Mason and Brandehoff (2020) EM:Rap 20(9): 13-4
  4. Dart (2001) Ann Emerg Med 37:181-8 [PubMed]
  5. Juckett (2002) Am Fam Physician 65(7):1367-74 [PubMed]
  6. McKinney (2001) Ann Emerg Med 37(2):168-74 [PubMed]