 Crotaline viper envenomation in the United States is treated with one of two licensed products: Wyeth Antivenin Crotalidae Polyvalent Polyvalent, or CroFab antivenin Crotalidae polyvalent immune Fab, ovine. In recent years, both of these products have been in critically short supply. Use of Wyeth Polyvalent has been associated with a greater than 75 incidence of adverse reactions, including acute type 1 and delayed type 2 immune reactions.These phenomena are an inherent risk in the use of whole immunoglobulin. CroFab s low molecular weight creates a pharmacokinetic mismatch with crotaline venom which leds to a recurrent venom effects. 