Antivenom, Crotalinae (Rattlesnake)
Pharmacology. Although two antivenoms are still available for the treatment of crotaline envenomation in some parts of the United States, production of the older product, Crotalinae polyvalent antivenom (equine), or Antivenom Crotalinae Polyvalent (Wyeth-Ayerst), has ceased, and it has been replaced by the newer Crotalinae polyvalent immune Fab (ovine), or CroFab (Protherics). To produce the polyvalent Fab antivenom, sheep are hyperimmunized with pooled venom from four North American snakes: Crotalus adamanteus, Crotalus atrox, Crotalus scutulatus, and Agkistrodon piscivorus. Papain then is added to the pooled serum product collected from the donor animals to cleave the immunogenic Fc fragment from the IgG antibody. The result is an affinity-purified Fab fragment antivenom. After administration, the antivenom is distributed widely throughout the body, where it binds to venom. Some remaining stocks of the Wyeth product may be found in parts of the United States.
Indications. Antivenom is used for treatment of significant envenomation by Crotalinae species (Table III–4 and See Snakebite).
Table III-4 Initial Dose of Crotalinae Antivenom
Table III-4 Initial Dose of Crotalinae Antivenom
Initial Dose (No. of Vials)
Severity of Envenomation
Antivenom Crotalinae Polyvalent (Wyeth)
CroFab (Protherics)
None or minimal
None
None
Mild (local pain and swelling)
5
4
Moderate (proximal progression of swelling, ecchymosis, mild systemic symptoms)
10
4–6
Severe (hypotension, rapidly progressive swelling and ecchymosis, coagulopathy)
15
6–12
Contraindications. Known hypersensitivity to the antivenom or to horse serum is a relative contraindication for the Wyeth product; antivenom may still be indicated for severe envenomation despite a patient history of allergic reaction. Known hypersensitivity to sheep or sheep serum, or to papain or papayas, is a contraindication for the CroFab product.
Adverse effects
Immediate hypersensitivity reactions (including life-threatening anaphylaxis) may occur to both products, even in patients with no history of animal serum sensitivity and negative skin test results. Skin testing is not
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