Crotalidae Polyvalent Immune Fab (ovine) was launched as CroFab? in the US for the
treatment of North American crotalid snake envenomation. It is the second antivenom to
be commercialized over fifty years after Antivenin (Crotalidae) Polyvalent (equine) from
Wyeth Labs. CroFab? is prepared by purification of Fab immunoglobulin fragments
obtained from the blood of healthy sheep flocks immunized with one of the following North
American snake venoms: Crotalus atrox (Western Diamondback rattlesnake), Crotalus
adamanteus (Eastern Diamondback rattlesnake), Crotalus scutulatus (Mojave rattlesnake),
and Agkistrodon piscivorus (Cottonmouth or Water Moccasin). The final preparation is
achieved by mixing the four different monospecific antivenins after fractionating the
immunoglobulin G from the ovine serum, cleaving the whole antibody into Fab and Fc
fragments with papain and isolating each of the venom-specific Fab fragments on ion
exchange and affinity chromatography columns. CroFab? acts by binding and neutralizing
venom toxins, facilitating their redistribution away from target tissues and their elimination
from the body. In infected mice, CroFab? was found to be 3-9 times more potent than
Antivenin (Crotalidae) Polyvalent (equine) for the prevention of lethality of nine venoms. In
a randomized clinical trial, initial control of envenomation was achieved in all patients
treated with intravenous administrations of CroFab?. The risk of hypersensitivity is
decreased with this mixture of specific antivenins compared to Antivenin (Crotalidae)
Polyvalent (equine) due to the absence of the Fc components of the immunoglobulin. The
elimination half-life of CroFab? ranged from approximately 12 to 23 hours, which is
relatively short for an antibody.
