Description
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.
Veterinary Drugs and Treatments
The equine-derived product is indicated for the treatment of envenomation
from most venomous
snake bites (pit vipers) in North
America and those caused by several species found in Central
and South America (fer-de-lance, Central and South American
Rattlesnake). The ovine-derived product is indicated for North
American Crotalid snake envenomation in humans, but has been
used in dogs. There is a fair amount of controversy with regard to
use of these products in domestic animals. The risks of administration
(e.g., anaphylaxis—
see below) may outweigh their potential
benefits in certain circumstances. However, these agents can be life
saving when given early in select situations. Many factors contribute
to the potential
for toxicity (victim’s size and general health, bite
site(s), number of bites, age, species and size of snake, etc.).
