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INTRODUCTION

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Definitive management of North American venomous snakebites is antivenom and supportive care. 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.

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HISTORY

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Crotalidae Polyvalent Immune Fab (Ovine)

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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.16 Wyeth has since stopped production of ACP, and all extant lots have expired. Many physicians still recall the use of this product, but new antivenoms have replaced ACP and have improved the approach to snakebite treatment. In October 2000, the US Food and Drug Administration (FDA) approved Crotalidae polyvalent immune Fab (FabAV), manufactured by BTG International (West Conshohocken, PA). This product is marketed as CroFab. This antivenom is derived from sheep serum and formulated specifically to treat snakebites from US Crotalinae species. It is an effective and less allergenic alternative to the previously manufactured horse serum product from Wyeth.16,33

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Antivenin (Micrurus fulvius) (Equine)

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For decades, Wyeth Laboratories (Marietta, PA) manufactured Antivenin (Micrurus fulvius) (Equine), which is more commonly known as North American Coral Snake Antivenin (NACSA), for treatment of envenomations by the eastern coral snake (Micrurus fulvius) and Texas coral snake (Micrurus tener). Wyeth discontinued production of this antivenom. The last remaining lot (# 4030026) was labeled with an expiration date of October 31, 2008. However, the US Food and Drug Administration extended the expiration date based on stability and potency data to October 31, 2013. Additionally, lot 4030024 has a new expiration date of April 30, 2015.35

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PHARMACOLOGY

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Crotalidae Polyvalent Immune Fab (Ovine)

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Chemistry/Preparation.
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Crotalidae polyvalent immune Fab (FabAV) is produced by inoculating sheep with the venom of one of the following crotaline snake species: the eastern diamondback rattlesnake (Crotalus adamanteus), western diamondback rattlesnake (Crotalus atrox), cottonmouth (Agkistrodon piscivorus), and Mojave rattlesnake (Crotalus scutulatus). The species specific antivenom is then prepared by isolating the antibodies from the sheep serum and digesting the IgG antibodies with papain. The venom-specific Fab antibody fragments are then isolated by affinity purification. This refining process eliminates most of the Fc portion of the immunoglobulin and other potentially immunogenic sheep proteins. Manufacturing specifications require ≤1.0% w/w for Fc fragments and ≤0.3% w/w for albumin.14 All four species ...

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