Efficacy, safety, and use of snake antivenoms in the United States.

The mainstay of hospital treatment for venomous snakebite is antivenom. There is currently only one antivenom available in the United States for the treatment of pit viper envenomation, Antivenin (Crotalidae) Polyvalent (ACP). The general indication for the administration of antivenom is presence of progressive venom injury. Progressive injury is defined as worsening local injury (eg, swelling, ecchymosis), a clinically important coagulation abnormality, or systemic effects (eg, hypotension, altered mental status). Unfortunately, there are no prospective data available regarding the efficacy of ACP. The efficacy of a new antivenom (CroFab; FabAV) composed of purified Fab specific to indigenous snake species has been demonstrated in prospective trials. FabAV appears as effective as IgG antivenoms. However, Fab molecules have a shorter half-life than IgG molecules and may allow recurrence of venom effects, if additional doses are not administered. It has also been found that other antivenoms, including ACP, also allow recurrence of venom effects. The Fab preparation has produced fewer acute or delayed (serum sickness) allergic reactions; however, further experience is needed to confirm this observation. Evaluation of this new antivenom has led to advances in our understanding of antivenoms in terms of solubility and durability. Fab fragments enter solution quickly, thereby shortening the time to antivenom administration and are remarkably stable under extreme conditions of heat and handling.