What are the guidelines for administering snake venom antiserum (antivenom) to patients presenting with symptoms of snake envenoming?

Guidelines for Snake Venom Antiserum Administration

The mainstay of treatment for venomous snakebites is antivenom administration, which should be done in a hospital setting with monitoring for adverse reactions. 1

Indications for Antivenom

• Administer antivenom when there is evidence of progressive venom injury:
  • Worsening local injury (swelling, ecchymosis)
  • Clinically important coagulation abnormality
  • Systemic effects (hypotension, altered mental status) 2

Initial Management

• Call emergency services immediately 1
• Apply pressure immobilization bandage (40-70 mmHg for upper extremity, 55-70 mmHg for lower extremity) to reduce venom spread, except for North American pit vipers 1
• Rest and immobilize the bitten extremity 1
• Remove rings and other constricting jewelry from the affected limb 1
• Avoid harmful methods: suction, ice, electric shock, tourniquets 1

Diagnostic Evaluation

• Complete blood count, coagulation studies, renal function tests, electrolytes
• Cardiac monitoring
• Assess for hemolysis, anemia, coagulopathy, and acute kidney injury 1
• Monitor oxygen saturation and provide supplemental oxygen if hypoxic 1

Antivenom Administration

Types of Antivenom

• Equine-derived antivenin (traditional standard of care)
• Sheep-derived antigen binding fragment (CroFab) - less allergenic 1

Dosing Considerations

• Evidence suggests that lower doses of antivenom can be as effective as higher doses in certain cases of neurotoxic envenomation 3
• Early administration (within 6 hours) is more effective at preventing complications such as myotoxicity 4

Administration Protocol

1. Prepare for potential allergic reactions before administration:

   • Have epinephrine, antihistamines, and corticosteroids readily available
   • Ensure resuscitation equipment is accessible

2. Administer antivenom intravenously in a monitored setting

3. Monitor closely for:

   • Acute reactions (anaphylactic or pyrogenic) - typically within the first hour 5
   • Delayed reactions (serum sickness) - onset between 5-14 days after administration 5

Potential Complications and Management

Adverse Reactions

• Acute hypersensitivity reactions occur in approximately one-third of patients receiving antivenom, with severe anaphylaxis in about 17% 4
• Serum sickness may develop 5-14 days after administration 5

Special Populations

• Pregnant women should receive appropriate antivenom when indicated, with maternal and fetal monitoring 1
• Patients with sickle cell disease require close monitoring for vaso-occlusive crisis triggered by envenomation 1

Follow-up Care

• Monitor for delayed reactions to antivenom, such as serum sickness
• Provide wound care and monitoring for infection 1
• Follow coagulation parameters until normalized

Important Caveats

• Antivenom is most effective when administered early; it may not effectively reduce local tissue damage if delayed
• The risk-benefit ratio must be considered, given the high rate of adverse reactions
• Fab fragments (CroFab) have a shorter half-life than traditional antivenoms and may require additional dosing to prevent recurrence of venom effects 2
• Skin testing has poor predictive value for identifying patients likely to experience allergic reactions to equine-derived antivenom 6