New Publication Compares Total Vials of CroFab® and Anavip® Administered to Treat US Rattlesnake Envenomation

Analysis shows patients treated with CroFab® require fewer total vials of antivenom, and fewer administrations to achieve control, than Anavip.

West Conshohocken, PA, May 02, 2023 (GLOBE NEWSWIRE) -- BTG Pharmaceuticals, a SERB company, today announced the publication of a new analysis of data from the American College of Medical Toxicology’s North American Snakebite Registry (NASBR) comparing the total vials of CroFab® [Crotalidae Polyvalent Immune Fab (Ovine)] and Anavip® [crotalidae immune F(ab′)2 (equine)] antivenom used to treat rattlesnake envenomation. The analysis was published in the Journal of Medical Toxicology.1

This data, collected between 2019 and 2021, considered 101 patients receiving CroFab® and 110 patients receiving Anavip®. To avoid bias, the authors excluded envenomation from copperhead (Agkistrodon) species in their analysis as so few in the NASBR database received Anavip®. The analysis found that:

  • The total number of vials of CroFab® was significantly less than the number of vials of Anavip® required for the treatment of rattlesnake envenomations, at a ratio of 1.8 vials of Anavip to 1 vial of CroFab® (P<0.0001). 
  • The median number of CroFab® vials administered to achieve control was significantly less than the median vials of Anavip® used to achieve control. (10 vials vs 18 vials; P<0.0001). 
  • According to the data, 39% of patients treated with CroFab® required more than one dose and 69% of patients treated with Anavip® required more than 1 dose (P<0.0001). 
  • There was no significant difference observed in treatment time between CroFab® (median 5.5 hours) compared to Anavip® (median 6.5 hours).
  • There was no significant difference in administration events or hospital length of stay.

“This analysis offers the first nationwide comparison of treatment characteristics of patients since both antivenoms have been widely available,” said Richard Dart, MD, Director of the Rocky Mountain Poison and Drug Center, and one of the paper’s authors. “Increased administration clearly has cost implications for envenomated patients and hospitals stocking antivenoms, and so it is worth understanding how different antivenoms are being used in practice.”

“We believe antivenom decisions should be based on clinical data and what’s best for patients,” said Thomas Kolaras, US Chief Commercial Officer of BTG Pharmaceuticals. “But where cost does come into the equation, hospitals and health systems need to consider the total cost of treatment rather than the cost per vial. We will continue to support the science and the understanding of vial ratios in the coming years as treatment practices evolve.”

CroFab® is the only antivenom derived from geographically and clinically relevant US snakes for comprehensive coverage of all North American pit viper envenomations.2,3 CroFab® uses an affinity purification process to eliminate nonspecific antibodies and increase the purity of the Fab fragments in each vial that rapidly bind to and neutralize venom toxin.2,3 CroFab® is backed by more than 20 years of clinical experience.3

About BTG Pharmaceuticals

BTG, a SERB company, is dedicated to helping healthcare providers treat patients with critical conditions, focusing on emergency care and rare diseases. For over 30 years we have helped treat complex and life-threatening conditions; supporting clinicians, healthcare systems and governments while offering hope to patients and their families. As a fully integrated company, we have the experience and capabilities to acquire, develop, and manufacture our medicines to the highest standards, and make them available worldwide through our secure supply chain.  


Brandehoff, N., Dalton, A., Daugherty, C. et al. Total CroFab and Anavip Antivenom Vial Administration in US Rattlesnake Envenomations: 2019–2021. J. Med. Toxicol. (2023).

2. WHO Expert Committee on Biological Standardization. WHO Technical Report Series, No. 1004, Annex 5; 2017. Accessed June 13, 2022.

3. CroFab®Prescribing information. BTG International Inc.; August 2018. 

Anavip® is a registered trademark of Laboratorios Silanes S.A. De C.V. Corporation Mexico Av. Paseo De Las Palmas 340 Lomas De Chapultepec, Miguel Hidalgo Mexico City Mexico 11000.


CroFab® Crotalidae Polyvalent Immune Fab (Ovine) is a sheep-derived antivenin indicated for the management of adult and pediatric patients with North American crotalid envenomation. The term crotalid is used to describe the Crotalinae subfamily (formerly known as Crotalidae) of venomous snakes which includes rattlesnakes, copperheads and cottonmouths/water moccasins.

Important Safety Information


Do not administer CroFab® to patients with a known history of hypersensitivity to any of its components, or to papaya or papain unless the benefits outweigh the risks and appropriate management for anaphylactic reactions is readily available.

Warnings and Precautions

Coagulopathy: In clinical trials, recurrent coagulopathy (the return of a coagulation abnormality after it has been successfully treated with antivenin), characterized by decreased fibrinogen, decreased platelets, and elevated prothrombin time, occurred in approximately half of the patients studied; one patient required re-hospitalization and additional antivenin administration. Recurrent coagulopathy may persist for 1 to 2 weeks or more. Patients who experience coagulopathy due to snakebite should be monitored for recurrent coagulopathy for up to 1 week or longer. During this period, the physician should carefully assess the need for re-treatment with CroFab® and use of any type of anticoagulant or anti-platelet drug.

Hypersensitivity Reactions: Severe hypersensitivity reactions may occur with CroFab®. In case of acute hypersensitivity reactions, including anaphylaxis and anaphylactoid reactions, discontinue infusion and institute appropriate emergency treatment. Patients allergic to papain, chymopapain, other papaya extracts, or the pineapple enzyme bromelain may also have an allergic reaction to CroFab®. Follow-up all patients for signs and symptoms of delayed allergic reactions or serum sickness (e.g., rash, fever, myalgia, arthralgia).

Adverse Reactions

The most common adverse reactions (incidence ≥ 5% of subjects) reported in the clinical studies were urticaria, rash, nausea, pruritus and back pain. Adverse reactions involving the skin and appendages (primarily rash, urticaria, and pruritus) were reported in 12 of the 42 patients. Two patients had a severe allergic reaction (severe hives and a severe rash and pruritus) following treatment and one patient discontinued CroFab® due to an allergic reaction. Recurrent coagulopathy due to envenomation and requiring additional treatment may occur.

Please see full Prescribing Information.


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