COMPARISON OF A NEW OVINE ANTIGEN-BINDING FRAGMENT (FAB) ANTIVENIN FOR UNITED-STATES CROTALIDAE WITH THE COMMERCIAL ANTIVENIN FOR PROTECTION AGAINST VENOM-INDUCED LETHALITY IN MICE

Snake venom poisoning is a medical emergency requiring immediate atten tion and the exercise of considerable judgment. Of the estimated 8,000 bites inflicted by venomous snakes in the United States each year, ap proximately 6,000 are treated with commercial antivenin. The only comm ercially available antivenin for North American Crotalidae envenomatio n is Antivenin (Crotalidae) Polyvalent (equine origin) (ACP; Wyeth Lab oratories, Philadelphia, PA). A common complication is the high incide nce of hypersensitivity reactions, occurring in more than 75% of patie nts treated with ACP. To minimize these side effects, a novel, affinit y-purified, antigen binding fragment (Fab) antivenom (FabAV) for Crota lidae venom poisoning has been produced from the sera of sheep. The ne w product is Antivenin Polyvalent Crotalid (Ovine) Fab (Crotab(TM); Th erapeutic Antibodies, Inc., Nashville, TN). The current report compare s the potencies in mice of FabAV and ACP against venom-induced lethali ty. The results indicate that FabAV is 3.1-9.6 times more potent than ACP for the prevention of lethality of the nine United States venoms t ested. For one of the venoms, Crotalus viridis helleri, FabAV was effi cacious while ACP was not.