I grew up on a military base near a small border town in New Mexico. As a child of the 90s, the ideas of what were considered reasonable and safe childhood activities differed greatly from today's standards. A shining example of this was at Moore's Trading Post, a local pawn shop and military surplus store just a few miles from the city limits. They were most famous for their rattlesnake pit near the entrance to the shop.
For the bargain price of one dollar, you could dangle a balloon attached to a fishing rod down into the snake pit, taunting the various rattlesnakes until one of them became annoyed enough to strike at the balloon. A large plexiglass barrier separated the local children from the pit, and five bucks was usually more than enough to keep your child entertained while you browsed the shop looking for good deals (or a grenade if you were so inclined).
One evening in the ED, toxicologist Dr. Will Rushton stared at me with a mixture of shock and disbelief as I waxed nostalgic about my childhood memories of hitting rattlesnakes in the head with a balloon while my father browsed pocket knives and camera equipment.
We had a good laugh about the absurdity of the situation, and thankfully, no children were ever harmed to the best of my knowledge. Snake bites, however, remain a very real and very serious reason for ED visits, and in our ERcast segment, "Antivenom," host Matt DeLaney sits down with Dr. Rushton to talk about all things antivenom.
Snake Bite Symptoms and Damage
Damage from snake bite envenomation falls into one of three categories:
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▪️Cytotoxic tissue damage resulting in ecchymosis, hemorrhagic bullae, and edema that can involve joints.
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▪️Coagulopathy in the form of:
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▪️Venom-induced thrombocytopenia leads to platelet dysfunction and destruction.
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▪️Venom-induced consumptive coagulopathy resulting from fibrinogen damage will often present like DIC without the shower emboli.
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▪️Neuromuscular issues such as paresthesias, and, in severe cases, respiratory depression.
How Is Antivenom Made?
Antivenom is produced by injecting horses or sheep with venom, which results in antibody production in the animal in response to the venom. The antibodies are then isolated from collected serum and used to create antivenom.
Antivenom Treatment Options
You’ll typically encounter two antivenom treatments:
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▪️Crotalideae polyvalent immune Fab (FAB) is made from sheep serum using the venom of four snakes indigenous to the United States.
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▪️Some evidence suggests that FAB is better at neutralizing whole venom and may be more effective for treating tissue damage.
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▪️Crotalidae immune F(ab)2 (FAB2) has only recently become available for use in the United States, but has been previously used in other countries such as Mexico.
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▪️FAB2 is made from the venom of two snakes non-indigenous to the United States.
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▪️Some evidence suggests that FAB2 may better treat coagulopathy in snake bite victims.
Which Antivenom Should You Use?
It depends on the clinical picture:
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▪️If tissue damage is the primary concern, FAB (CroFab) might be preferred
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▪️If coagulopathy is prominent, FAB2 (Anavip) may offer better results
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That said, many hospitals only stock one type of antivenom—and that’s okay. The most important thing is to start treatment quickly. Don’t delay care trying to transfer the patient to a facility that carries a specific product. When it comes to snake bite treatment, timing matters more than the brand.
Snake bites still happen—and when they do, antivenom saves lives. Understanding the mechanism of injury, knowing how antivenom is made, and making confident, timely treatment decisions can make all the difference.
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