Hypersensitivity reactions due to North American pit viper antivenom administration and confirmed elevation of alpha-gal IgE

The two current antivenom products available in the United States (US) for North American pit viper envenomation include ovine-derived Crotalidae polyvalent immune Fab (FabAV, Crofab®) and equine-derived Crotalidae Immune (F(ab′)2, Anavip®). Both products contain the oligosaccharide, galactose-alpha-1,3-galactose (alpha-gal), and may lead to a hypersensitivity reaction commonly referred to as alpha-gal syndrome (AGS). We report two patients receiving antivenom for pit viper envenomation who developed anaphylactic reactions and had confirmed abnormal titers of alpha-gal-specific IgE. We suggest clinicians seek a history of red meat allergy and administer AV cautiously in endemic areas of AGS.