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Treatment with CroFab®

How CroFab® is made

CroFab® Crotalidae Polyvalent Immune Fab (Ovine) is manufactured using venom from 4 common types of North American pit vipers that are indigenous to the United States:

  • Western diamondback rattlesnake

  • Eastern diamondback rattlesnake

  • Mojave rattlesnake

  • Cottonmouth (water moccasin)

These 4 snake venoms were specifically selected based on several criteria:

  • Their clinical importance in snakebite cases in the United States
  • The wide geographic range of these snakes
  • Genetic dissimilarities of the immunizing venoms
  • Cross-reactivity with 10 other clinically important North American crotalid snake venoms

Step 1:
Immunogens from each of the 4 North American pit viper venoms* are produced in a laboratory.

Step 2:
Immunogens from each venom are used to immunize separate flocks of sheep to ensure a consistent and uniform product.

  • The immunogens are recognized by the ovine immune system as foreign antigens, to which antibodies are produced

Step 3:

  • Antibodies are separated and cleaved with papain
  • The Fc fragment and undigested immunoglobulin G are separated from the Fab fragments through column affinity purification
  • This purification process may reduce hypersensitivity reactions

Step 4:

  • To obtain the final antivenom product, the 4 different monospecific antivenoms are mixed and standardized

The resulting product is formulated into the antivenom CroFab®.

*Western diamondback rattlesnake, eastern diamondback rattlesnake, Mojave rattlesnake, and cottonmouth (water moccasin).

Our commitment to ethical practices
BTG is committed to strict adherence to ethical research and development practices. We believe the rights, safety, and well-being of the trial subjects prevail over the interests of science and society. Thus, we respect the safety of clinical research participants and our clinical trials are performed in accordance with the listed directives, regardless of where they are performed. We ensure that all medical care and medical decisions made on the behalf of research participants are the responsibility of a qualified physician. We ensure that all patient data is recorded confidentially and handled and stored in a way that allows accurate reporting, interpretation, and verification according to best practice, including reporting of adverse clinical events.

Our policy is that the use of animals in research will be performed to the highest standard of ethics, adhering to the three guiding principles of reduction, refinement and replacement. All animal studies are performed at external Clinical Research Organizations (CROs) and academic units, and we will only work with external parties that evaluate animal studies using a local ethical review process. In addition, we will only perform animal studies in territories where they are strictly regulated. Alternatives to animal use will always be assessed and in vitro testing performed as an alternative wherever possible.

CALL 1-844-293-0007.


CroFab® Crotalidae Polyvalent Immune Fab (Ovine) is an antivenin indicated for the management of patients with North American crotalid envenomation. The term crotalid is used to describe the Crotalinae subfamily (formerly known as Crotalidae) of venomous snakes that includes rattlesnakes, copperheads, and cottonmouths/water moccasins. Early use of CroFab® (within 6 hours of snakebite) is advised to prevent clinical deterioration and the occurrence of systemic coagulation abnormalities.

Important Safety Information

The most common adverse events reported in clinical studies were mild or moderate reactions involving the skin and appendages (primarily urticaria, rash, or pruritus), which occurred in 14 out of 42 patients. Three patients experienced a serious adverse event. Two patients had a severe allergic reaction (severe hives and a severe rash and pruritus) following treatment. One patient had a recurrent coagulopathy due to envenomation, which required rehospitalization and additional antivenin administration. 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. 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. One patient discontinued CroFab® therapy due to an allergic reaction. Anaphylaxis and hypersensitivity reactions can occur, and patients should be monitored closely during treatment. Patients with allergies to papain, chymopapain, other papaya extracts, or the pineapple enzyme bromelain may also be at risk for an allergic reaction to CroFab®. CroFab® contains mercury in the form of ethyl mercury from thimerosal. The final product contains up to 30 mcg or approximately 0.03 mg of mercury per vial, which amounts to no more than 0.6 mg of mercury per dose (based on the maximum dose of 18 vials studied in clinical trials of CroFab®).