A Comparison of Crotalinae Equine Immune F(ab)2 Antivenom (Anavip) and Crotalidae Polyvalent Immune Fab,

The overall objective of this Phase 2 open-label comparative study was to demonstrate that the F(ab)2 antivenom Anavip has significantly longer plasma persistence than does Fab, and that this is associated with a slower rise in venom levels and slower decline in platelet count and fibrinogen following hospital discharge of envenomated subjects. The effectiveness of F(ab)2 in preventing the recurrence of coagulopathies after the subject's discharge from hospital will indicate that, inherently, F(ab)2 antivenom has an improved safety profile relative to the Fab antivenom CroFab in treating envenomation by crotaline vipers. Each subject was assessed for quantitative serum venom levels. Relatively few historical data exist to support the use of venom levels as a surrogate endpoint in envenomation. However, changes in venom levels have been correlated with coagulopathic effects, during both the acute phase of venom toxicity and the post treatment period of recurrent venom effect. Validation of this surrogate endpoint via correlation of venom effect with platelet count and fibrinogen level in this phase II study is intended to support future studies. The secondary endpoints were the determination of coagulation abnormalities during the follow up period.