Anti-Snake Venom (ASV) Dosage and Administration Guidelines
The optimal approach to anti-snake venom (ASV) administration is to use a loading dose followed by continuous infusion until clinical improvement, with dosage based on envenomation severity and monitoring for early adverse reactions.
Initial Assessment and Decision to Administer ASV
ASV is indicated for patients with progressive venom injury, defined as:
- Worsening local injury (swelling, ecchymosis)
- Clinically important coagulation abnormality
- Systemic effects (hypotension, altered mental status)
Emergency services should be activated for any person bitten by a venomous or possibly venomous snake 1
ASV Dosing Regimens
Recommended Approach Based on Envenomation Severity
Mild Envenomation:
- Loading dose: 30 ml ASV
- Followed by: 30 ml continuous infusion every 6 hours
- Continue until: Two consecutive normal coagulation times (CT) at 6-hour intervals
- Additional: 30 ml over 24 hours after normalization 2
Moderate to Severe Envenomation:
- Loading dose: 70 ml ASV
- Followed by: 30 ml continuous infusion every 6 hours
- Continue until: Two consecutive normal coagulation times (CT) at 6-hour intervals
- Additional: 30 ml over 24 hours after normalization 2
Duration of Administration
- Each dose should be infused over 30-60 minutes to reduce risk of early adverse reactions 3
- Continuous monitoring is essential for at least 2 hours after administration 3
Monitoring and When to Stop ASV
Parameters to Monitor
- Coagulation parameters (whole blood clotting time, PT/INR, aPTT)
- Local progression of swelling and tissue damage
- Vital signs
- Systemic symptoms (neurological status, bleeding)
Criteria for Stopping ASV
- Primary Endpoint: Two consecutive normal coagulation tests 6 hours apart 2
- Secondary Considerations:
- Resolution of progressive swelling
- Improvement in systemic symptoms
- Stabilization of vital signs
Managing Adverse Reactions to ASV
- Early adverse reactions (EARs) occur in approximately 22.5% of patients receiving ASV 3
- All EARs occur within 2 hours of administration 3
Management of Reactions
Prepare resuscitation equipment before ASV administration
For mild reactions (urticaria, pruritus):
- Temporarily stop ASV infusion
- Administer antihistamines
- Resume at slower rate if symptoms resolve
For severe reactions/anaphylaxis:
Supportive Care
- Rest and immobilize the bitten extremity 1
- Remove rings and other constricting objects from the bitten extremity 1
- Avoid application of ice, use of suction, electric shock, tourniquets, or pressure immobilization bandaging, as these are potentially harmful 1
- Clean the area with mild soap and water 4
- Elevate the affected limb if possible 4
Special Considerations
- Continuous infusion regimens have been shown to require significantly less total ASV compared to intermittent bolus dosing (179-233 ml vs. 343-433 ml for moderate-severe envenomation) 2
- Recurrence of coagulopathy is less common with continuous infusion regimens 2
- Higher initial doses (70 ml vs. 30 ml) result in faster normalization of coagulation parameters in severe envenomation 2
Common Pitfalls to Avoid
- Underdosing: Using too little ASV may lead to progression of envenomation and increased risk of complications 5
- Delayed administration: ASV should be given as soon as indications are present
- Inadequate monitoring: Patients should be observed continuously for at least 2 hours after ASV administration 3
- Failure to prepare for adverse reactions: Always have resuscitation equipment ready before ASV administration
By following these guidelines, clinicians can optimize the use of ASV to effectively treat snake envenomation while minimizing risks and conserving resources.