Safe administration of Crotalidae equine immune F(ab')2 antivenom in a patient who suffered anaphylaxis from Crotalidae polyvalent immune Fab antivenom.

Allergic reactions to Crotalidae polyvalent immune Fab and Crotalidae immune F(ab')2 are uncommon but potentially life-threatening. It is unknown whether cross-reactivity reactions exist between these two antivenoms. We report a case of a patient who suffered anaphylaxis from Crotalidae polyvalent immune Fab but subsequently was safely administered Crotalidae immune F(ab')2 after a presumed Agkistrodon contortix (copperhead) envenomation. This single case supports the safety of Crotalidae immune F(ab')2 administration in patients with a history of anaphylaxis to Crotalidae polyvalent immune Fab treatment.