Drug Criteria & Outcomes
CroFab: A treatment for snakebites
By Mary Juanita Meeks, PharmD*
Birmingham, AL
* Written as a PharmD candidate at Samford University
Crotalidae Polyvalent Immune Fab-Ovine (CroFab) is an antivenom that was approved for the treatment of snakebites in October 2000. CroFab is indicated for patients with minimal or moderate North American crotalid envenomation. Early use (defined as within six hours of the envenomation) is recommended to prevent deterioration and systemic coagulation abnormalities.
Wyeth-Ayerst announced its decision to stop the production of its polyvalent antivenin once CroFab became available. For years, Wyeth’s polyvalent product was the principal snakebite antivenom to treat snakebites related to the continental United States. This polyvalent antivenin was manufactured from horse serum, which contributes to a high rate of serum sickness reactions. CroFab is manufactured from sheep serum, and the chemical moiety in horse serum that contributed to serum sickness reaction is absent in the newer product.
The active part is a Fab fragment of immunoglobulin G that binds and neutralizes venom toxins to prevent the destruction in target tissues. This makes CroFab less likely to cause serum sickness, although the possibility still exists. The lack of moiety allows physicians to treat patients who normally would not be treated (i.e., in patients who risk possible side effects that are more severe than the snakebite effect itself). This is especially true with copperhead bites that tend not to be as severe.
There are limited data comparing CroFab to other antivenoms. Only two clinical trials using CroFab have been completed so far, but other trials are planned or in progress. One benefit noticed during a clinical trial was that patients who had developed thrombocytopenia before treatment with CroFab had much faster normalization of platelet count after CroFab administration and clinical stabilization. The platelet count recovery normally takes several hours to several days after a patient has been bitten.
Papaya is used to cleave the whole antibody into its active garments; thus, traces of papaya may be found in CroFab. Therefore, CroFab should not be administered to patients who have a known hypersensitivity to papaya or papain unless the benefits outweigh the risks.
Caution also should be used if administering CroFab to nursing women, as CroFab may appear in breast milk. Geriatric and pediatric studies have not been conducted, although the weight-based dose required for children is believed to be the same as in adults. The product must be refrigerated and used within four hours of reconstitution.
Snakebite coverage for CroFab includes:
- Western diamondback rattlesnake;
- Eastern diamondback rattlesnake;
- Mojave rattlesnake; and
- cottonmouth or water moccasin.
CroFab also is believed to cover certain species closely related to those listed above.
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