What is the recommended dose of antivenom (antivenin) for a patient with a viper bite?

Recommended Antivenom Dose for Viper Bite

The recommended initial dose of antivenom for viper bite is 10 vials administered intravenously, which provides adequate venom neutralization without increasing adverse reaction risk compared to lower doses. 1, 2, 3

Initial Dosing Protocol

• Administer 10 vials of polyvalent anti-snake venom (ASV) as the starting dose for all viper envenomations requiring antivenom therapy. 1, 2, 3
• This 10-vial dose represents the optimal balance between efficacy and safety—it is sufficient as a single dose for most cases while avoiding the pitfall of inadequate initial dosing (such as 2 vials) which necessitates multiple rounds without improving outcomes. 2
• Hospitals should stock 12-18 vials to ensure adequate initial treatment capacity, with the American College of Emergency Physicians recommending 12 vials available for most North American pit viper envenomations. 1, 2

Preparation and Administration

• Dilute the ASV in normal saline (0.9% sodium chloride) at a ratio of 1:5 to 1:10. 2
• Administer intravenously over 1 hour via slow IV infusion using a dedicated IV line. 2
• Start the infusion slowly for the first 10-15 minutes while monitoring closely for hypersensitivity reactions. 2
• Remove all rings and constricting objects from the bitten extremity immediately before starting antivenom to prevent tissue damage from progressive swelling. 1, 2, 3

Additional Dosing Requirements

• Administer additional 5-10 vials every 4-6 hours if coagulation parameters remain abnormal after the initial dose. 2
• Administer additional 5-10 vials every 4-6 hours if new systemic symptoms develop. 2
• For neurotoxic envenomation (krait, cobra), ensure airway management equipment and ventilatory support capability are immediately available. 2, 3

Monitoring During Administration

• Monitor vital signs (blood pressure, heart rate, respiratory rate) every 15 minutes initially, then every 30 minutes. 2
• Watch for signs of anaphylaxis including urticaria, bronchospasm, hypotension, and angioedema. 2
• Use continuous cardiac monitoring via ECG. 2
• Monitor progression of local swelling and respiratory status, particularly for neurotoxic envenomation. 2

Managing Anaphylactic Reactions

• Have epinephrine immediately available: 0.01 mg/kg in children (up to 0.3 mg maximum) and 0.3-0.5 mg in adults, administered intramuscularly in the anterolateral thigh. 1, 2
• Stop ASV infusion immediately if anaphylaxis occurs. 2
• Provide airway support and supplemental oxygen as needed. 2
• Administer IV antihistamines and corticosteroids, but recognize these are not substitutes for epinephrine in treating anaphylaxis. 2

Critical Pitfalls to Avoid

• Do not use inadequate initial doses (such as 2 vials), as this prolongs the period of inadequate venom neutralization without improving outcomes. 2
• Do not apply tourniquets, ice, suction, or electric shock therapy—these interventions are ineffective and potentially harmful. 2, 3
• Do not routinely prescribe antibiotics, as they do not improve outcomes in viper envenomation. 4
• Avoid corticosteroids as routine treatment, as they do not improve selected endpoints or reduce edema. 4
• Do not use low-molecular-weight heparin, as it increases persistent functional discomfort and length of hospital stay. 4

Evidence Quality Note

The 10-vial recommendation comes from current guideline consensus 1, 2, 3, while older research on European vipers suggests single vials may suffice for some species 4. However, given the variability in venom toxicity and the higher risk profile of many viper species, the 10-vial initial dose provides a safer margin for North American and other highly venomous vipers. The key is early administration—antivenom given within 10 hours of the bite significantly reduces complications compared to delayed treatment. 4