When to stop Antivenom (AV) in a patient with a viper bite presenting with swelling in a limb?

When to Stop Antivenom in Viper Bite with Limb Swelling

Stop antivenom when local swelling progression has halted, systemic signs have resolved, and coagulation parameters have normalized or stabilized—typically requiring monitoring for recurrence of venom effects for at least 24-48 hours after the last dose. 1, 2

Indications to Continue Antivenom

The primary indication for ongoing antivenom administration is progressive venom injury, which includes: 1

• Worsening local swelling that continues to advance proximally toward the trunk 2, 3
• Clinically important coagulation abnormalities (elevated PT/INR, thrombocytopenia, hypofibrinogenemia) 1, 4
• Systemic effects such as hypotension, altered mental status, or neurotoxicity 1, 5

Criteria to Stop Antivenom

Discontinue antivenom when ALL of the following are achieved: 1, 2

• Local swelling has stopped progressing and begins to stabilize or regress 2, 3
• Coagulation parameters normalize (PT, INR, fibrinogen, d-dimer trending toward normal) 4
• Systemic signs resolve (blood pressure stabilizes, mental status clears) 1
• No new symptoms develop during observation period 5

Critical Monitoring Period After Stopping

Continue monitoring for at least 24-48 hours after the last antivenom dose because: 1, 5

• Recurrence of venom effects is common with both older IgG antivenoms and newer Fab preparations due to shorter half-life of antivenom compared to venom 1
• Delayed onset of clinical signs can occur several hours after envenomation 5
• Late coagulation abnormalities may emerge even after initial improvement 4

Specific Dosing Guidance

Administer antivenom in repeated doses until progression stops: 1, 3

• The typical dosing is 1-2 vials initially, with additional vials given based on clinical response 5
• Some cases require 6 or more vials for severe envenomation with marked local effects 3
• Reassess every 1-2 hours for progression of swelling or worsening laboratory parameters 4, 2

Common Pitfalls to Avoid

Do not stop antivenom prematurely based solely on lack of systemic symptoms: 2

• Clinicians often underestimate the morbidity of local venom effects and fail to administer adequate antivenom 2
• Marked progressive swelling alone is an indication for antivenom even without systemic signs 2
• Inadequately treated swelling can progress to the trunk and threaten vital structures (airways, urinary retention) even when the bite site is distal 2

Do not assume treatment is complete after initial improvement: 1

• Both Fab and IgG antivenoms allow recurrence of venom effects if additional doses are not given 1
• Monitor coagulation studies serially as they may worsen again after initial correction 4

Algorithm for Decision-Making

1. Initial assessment: Determine if progressive local injury, coagulation abnormality, or systemic effects are present 1
2. If YES: Administer antivenom and reassess in 1-2 hours 4, 3
3. Repeat antivenom if swelling continues to progress, coagulation worsens, or systemic signs persist 1, 2
4. Stop antivenom only when ALL progression has halted 2, 3
5. Continue monitoring for minimum 24-48 hours for recurrence 1, 5
6. Resume antivenom if any venom effects recur during observation 1