In addition to supportive care, antivenom provides definitive management of North American venomous snakebites. In the past, numerous treatments were advocated to prevent systemic absorption or to neutralize venom. These therapies included tourniquets, incision and suction, venom extractors, electrotherapy, and cryotherapy. All of these treatment modalities are either ineffective, delay time to definitive care, or harmful. The focus of treatment for the snakebite victim is a careful assessment, supportive care, evaluating for signs of envenomation, and ultimately, determining the need for antivenom.
Crotalidae Polyvalent Immune Fab (Ovine)
Historically, Wyeth (Marietta, PA) manufactured Antivenin Crotalidae Polyvalent (ACP) for treatment of crotaline snakebites in the United States. It was a poorly purified whole IgG product derived from horse serum with significant risk for acute and delayed allergic reactions.18 Wyeth stopped production of ACP, and any extant lots expired. Many physicians still recall the use of this product, but new antivenoms have replaced ACP, improving the approach to snakebite treatment. In October 2000, the US Food and Drug Administration (FDA) approved Crotalidae polyvalent immune Fab (Fab antivenom), manufactured by BTG International, marketed as CroFab. This antivenom is derived from sheep serum and formulated as an effective treatment for US Crotalinae species. In addition, because of papain digestion and the affinity purification, which removes extraneous proteins as well as the Fc portion of the antibody, Fab antivenom is a less allergenic alternative to the previously manufactured horse serum product from Wyeth (Table A39–1).18,37
TABLE A39–1Comparison of Crotalid and Elapid Antivenoms ||Download (.pdf) TABLE A39–1 Comparison of Crotalid and Elapid Antivenoms
|Snake Species Used in Production
Crotalidae Polyvalent Immune Fab
|4–6 vials repeated as needed to achieve control; then 2 vials every 6 h × 3 doses
Crotalidae Immune F(ab’)2
|10 vials repeated as needed to achieve control
|North American Coral Snake Antivenin
|3–5 vials repeated as needed for clinical improvement
Crotalidae Immune F(ab′)2 (Equine)
Equine-derived Crotalidae immune F(ab′)2 (Anavip; F(ab′)2 antivenom) manufactured by Instituto Bioclon, was recently approved by the FDA as an alternative treatment for North American Crotalidae, but its widespread availability is not expected until the fall of 2018. The historical experience with Fab antivenom has revealed the unexpected problem of recurrent venom effects that occur hours to days after completing treatment. Unlike the Fab antivenom, this F(ab′)2 product uses pepsin digestion, which keeps the Fab fragments joined to form a larger antibody complex and, as such, is expected to prolong the duration of action. Therefore, the benefits to this new F(ab′)2 antivenom ...