Pit Viper Antivenin
Antivenin (Crotalidae) Polyvalent
Also known as: CroFab · Pit Viper Antivenin · Crotalidae Polyvalent Immune Fab
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Pit viper envenomation | 1-2 vials of antivenin. Initially, give one vial, by diluting to 100-250 mL of crystalloid fluids and initially administer by slow IV | IV | prn | — | 🌎 NA |
| Pit viper envenomation | 1-5 rehydrated vials (10-50 mL) IV depending on severity of symptoms, duration of time after the bite, snake size, patient size. Additional doses may be given every 2 hours as required. If unable to give IV, may administer IM as close to bite as practical. | IV/IM | q2h as required | — | 🌎 NA |
- Pit viper envenomation: Adjust infusion volume in smaller patients to prevent fluid overload. Intravascular bites or bites to torso/tongue require prompt, aggressive administration.
- Pit viper envenomation: The smaller the victim, the larger the dose (venom amount/kg is higher).
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Pit viper envenomation | 1-2 vials of antivenin. Initially, give one vial, by diluting to 100-250 mL of crystalloid fluids and initially administer by slow IV | IV | prn | — | 🌎 NA |
- Pit viper envenomation: Adjust infusion volume in smaller patients to prevent fluid overload.
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Systemic effects of envenomation | 1-2 vials slowly IV diluted in 250-500 mL saline or lactated Ringer's | IV | prn | — | 🌎 NA |
- Systemic effects of envenomation: Use only if necessary to treat systemic effects. Administer antihistamines; corticosteroids are contraindicated.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Antivenin (Crotalidae) Polyvalent is a critical, life-saving antidote indicated for the treatment of envenomation from North, Central, and South American pit vipers (e.g., rattlesnakes, copperheads, cottonmouths, fer-de-lance).
- Formulations: Available as an equine-origin product (whole IgG antibodies) and an ovine-origin product (Fab fragments, e.g., CroFab®).
- Risks: Up to 50% of the veterinary-labeled equine product contains equine albumin and other proteins, carrying a significant risk of hypersensitivity reactions (anaphylaxis).
- Clinical Pearl: While the ovine Fab product (CroFab) is human-labeled, it is frequently used off-label in veterinary medicine. Fab fragments generally have a lower risk of anaphylaxis compared to whole-IgG equine products, though they have a shorter half-life and may require repeated dosing to prevent venom recurrence.
- Treatment requires aggressive supportive care and can be highly expensive.
Mechanism of action
Antivenins provide passive immunity to the patient.
- They contain concentrated serum globulins (or Fab fragments) obtained from animals (horses or sheep) hyperimmunized with pit viper venom.
- Mechanism: The immunoglobulins directly bind to and neutralize the complex toxic proteins and enzymes present in the venom.
- Effect → Rapidly reverses venom-related systemic signs and coagulation abnormalities.
- Note: Venom-induced thrombocytopenia, particularly from Timber Rattlesnakes, may be resistant to antivenin treatment.
Safety & warnings
Contraindications
- Known severe hypersensitivity to equine or ovine proteins (relative contraindication in life-threatening envenomation)
Adverse effects
- Anaphylaxis (Type I hypersensitivity)
- Anaphylactoid reactions
- Serum sickness (Type III hypersensitivity, delayed)
- Nausea
- Pruritus
- Hyperemia of the inner pinna
Precautions
High risk of anaphylaxis due to equine-origin proteins. A test dose (1:10 dilution intracutaneously) is sometimes suggested but evaluation is difficult. Slow IV administration is usually sufficient to identify reactive animals. Pre-treatment with diphenhydramine is highly recommended to sedate the patient and reduce allergic reactions. If an anaphylactoid reaction occurs (nausea, pruritus, pinna hyperemia), stop the infusion, administer additional diphenhydramine, and restart 5 minutes later at a slower rate.
Drug interactions
May mask the clinical signs associated with the venom; use with caution initially.
Theoretical risk of potentiating venom, though diphenhydramine is routinely and safely used by clinicians for pre-treatment.
May mask the early signs associated with anaphylaxis.
Generally out of favor for treating snakebite envenomation, but may be useful to treat secondary anaphylaxis. Contraindicated in horses per some references.
Reportedly not effective in treating the thrombin-like enzymes found in rattlesnake venom.
Monitoring
- Signs associated with an allergic response (anaphylaxis, anaphylactoid-reactions, serum sickness)
- CBC with platelets
- Coagulation parameters
- Biochemical profile
- Hydration status
- ECG
Overdose
Specific overdose information is not provided, but fluid overload is a significant risk in smaller patients receiving large volumes of crystalloid fluids used to dilute the antivenin.
Available products
Formulations
- Powder for injection (lyophilized)
Veterinary
- Antivenin (Crotalidae) Polyvalent Equine Origin single dose vial lyophilized; 10 mL vials with diluent (Antivenin - Fort Dodge)
Human-labeled
- Antivenin (Crotalidae) Polyvalent Powder for Injection (lyophilized): combo packs with 1 mL vial of normal horse serum and 10 mL Bacteriostatic water (Wyeth)
- Antivenin (Crotalidae) Polyvalent Immune Fab (Ovine Origin) Powder for Injection (lyophilized): 1 g total protein per single use vial (CroFab - Altana)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Do not store above 98°F (37°C); avoid freezing and excessive heat. Reconstitute gently by swirling (do not shake) to prevent foaming. Veterinary-labeled product should be used immediately after rehydration. Human equine product may be used within 4-48 hours depending on the reference. Ovine product (CroFab) should be refrigerated and used within 4 hours of reconstitution.
Client information
Medical Emergency: Snakebites are life-threatening emergencies. Immediate veterinary intervention is required.
- High Cost: Antivenin therapy is very expensive. Depending on the severity of the bite and the size of your pet, multiple vials may be necessary.
- Intensive Care: Treatment involves more than just the antivenin. Your pet will likely require hospitalization, aggressive IV fluid therapy, pain management, and continuous monitoring.
- Allergic Reactions: Because the antivenin is derived from horse or sheep proteins, there is a risk of severe allergic reactions (anaphylaxis) during administration, or delayed reactions (serum sickness) days to weeks later. Your veterinarian will monitor closely for these complications.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.