What is the proper administration and dosage of antivenom for a snake bite?

From the Guidelines

Antivenom administration for snakebites should be guided by the specific antivenom recommended, such as antivenin Crotalidae polyvalent immune Fab (ovine) (CroFab; FabAV), which is preferred over antivenin (Crotalidae) polyvalent due to its improved safety profile 1. The dosage and administration of antivenom vary based on the severity of envenomation and the specific product used.

• Typically, the initial dose is 4-10 vials given intravenously over 30-60 minutes.
• Before administration, patients should be tested for hypersensitivity with a small skin test dose.
• During infusion, vital signs must be closely monitored for signs of anaphylaxis.
• Additional vials may be administered if symptoms persist or worsen, with some severe cases requiring 20 or more vials. The amount of antidote needed to treat a 100-kg patient for either 8 hours or 24 hours should be considered, and hospitals should perform a hazard vulnerability assessment for each antidote to determine the appropriate amount to stock 1. Antivenom works by binding to and neutralizing venom proteins, preventing further tissue damage and systemic effects.
• Treatment is most effective when given within 4-6 hours of the bite, though it may still provide benefit when administered later.
• Supportive care, including pain management, wound care, and monitoring for compartment syndrome, is essential alongside antivenom therapy.
• Patients should be observed for at least 24 hours after antivenom administration to monitor for delayed reactions or recurrence of symptoms.

From the Research

Administration and Dosage of Antivenom

• Antivenom should be administered as soon as there is evidence of envenoming, such as venom-induced consumption coagulopathy, sudden collapse, myotoxicity, neurotoxicity, thrombotic microangiopathy, and renal impairment 2.
• One vial of the relevant antivenom is sufficient to bind all circulating venom, but recovery may be delayed as many clinical and laboratory effects of venom are not immediately reversible 2.
• The dosage of antivenom may vary depending on the severity of envenomation, with mild cases requiring up to five vials, moderate cases requiring 10 to 15 vials, and severe cases requiring 15 to 20 vials 3.
• Antivenin is effective only when administered intravenously, and skin testing to predict the possibility of anaphylactic reaction is mandatory before administration 3.

Preparation and Administration

• Antivenom should be prepared and administered by a clinician capable of treating complications such as anaphylaxis 2.
• Diphenhydramine and epinephrine should be readily available in case of anaphylaxis 3.
• The administration of antivenom should be done in a hospital with onsite laboratory facilities and appropriate antivenom stocks 2.

Considerations and Priorities

• Patients with suspected snakebite should be admitted to a suitable clinical unit for at least 12 hours after the bite, and serial blood testing and neurological examinations should be done for all patients 2.
• The priorities of care in treating venomous snakebites include timely transportation to facilities that stock and administer antivenom, and the use of pressure immobilization bandages and related strategies to delay onset of systemic toxicity 4.
• Serum sickness is a potential complication of antivenom administration, and can cause significant effects after the treatment of snake envenoming, but appears to respond well to corticosteroid treatment 5.