Acute adverse reactions in two pit viper antivenoms

There are two FDA-approved antivenoms for the treatment of North American pit viper envenomations: Crotalidae polyvalent immune Fab (ovine) and Crotalidae immune F(ab’)2 (equine). Previous publications have estimated the risk of acute adverse reactions to FabAV to be 1.4%–8%. There are fewer studies assessing the adverse reaction rate in Fab2AV. This study compared the incidences of acute adverse reactions between the two products. We retrospectively reviewed snakebites on which our toxicology service consulted between January 1, 2021 and November 1, 2023. Collected data included patient demographics, suspected snake species, antivenom use, adverse reactions to antivenom, and medications prescribed for these reactions. There were 226 snakebite patients, of whom 78 (34.5%) were female. Ages ranged from 18 months to 89 years old. We administered antivenom to 154 patients; 102 received Fab2AV and 52 were treated with FabAV. Acute adverse reactions occurred in 15 (14.7%) of the Fab2AV patients and in two (3.8%) patients managed with FabAV. In the Fab2AV group, two patients developed anaphylaxis. The two FabAV patients developed only pruritis. Acute adverse reactions were more common in patients treated with Fab2AV than with FabAV. The severity was also greater in the Fab2AV group.