Antivenin (Crotalidae) Polyvalent, Wyeth, is a refined and concentrated preparation of serum globulins obtained by fractionating blood from healthy horses immunized with the following venoms: Crotalus adamanteus (Eastern diamond rattlesnake), C. atrox (Western diamond rattlesnake), C. durissus terrificus (tropical rattlesnake, Cascabel), and Bothrops atrox ("Fer-de-lance''). Phenol, 0.25%, and thimerosal, 0.005%, are added as preservatives. The product is standardized by its ability to neutralize the lethal action of standard venoms by intravenous injection in mice.1 Dried from the frozen state, the lyophilized serum has a moisture content of less than 1% and is soluble on addition of the diluent contained in each package (Sterile Water for Injection, USP).

CroFab® [Crotalidae Polyvalent Immune Fab (Ovine)] is a sterile, nonpyrogenic, purified, lyophilized preparation of ovine Fab (monovalent) immunoglobulin fragments obtained from the blood of healthy sheep flocks immunized with one of the following North American snake venoms: Crotalus atrox (Western Diamondback rattlesnake), Crotalus adamanteus (Eastern Diamondback rattlesnake), Crotalus scutulatus (Mojave rattlesnake), and Agkistrodon piscivorus (Cottonmouth or Water Moccasin). To obtain the final antivenin product, the four different monospecific antivenins are mixed. Each monospecific antivenin is prepared by fractionating the immunoglobulin from the ovine serum, digesting it with papain, and isolating the venom-specific Fab fragments on ion exchange and affinity chromatography columns.