Treatment Drawbacks
Antivenins have been in use for decades and are the only effective treatment for some bites. "Antivenins have a fairly good safety record," says Don Tankersley, deputy director of FDA's division of hematology. "There are sometimes reactions to them, even life-threatening reactions, but then you're treating a life-threatening situation. It's clearly a case of weighing the risks versus the benefits."People previously treated with antivenin for snakebites probably will develop a lifelong sensitivity to horse products. To identify these and other sensitive patients, hospitals typically obtain a record of the victim's experience with snakebites or horse products. But some people with no history of such exposures may have become sensitive through contact with horses, or possibly exposure to horse dander, and not know they are sensitive. Others may be sensitive without any known or remembered contact with horses. So hospitals also perform a skin test that quickly shows any sensitivity. Some hypersensitive patients may even react severely to the small amount of antivenin used in the skin test. Hospitals have procedures for reviving patients with serious reactions. Some victims with positive skin tests can be desensitized by gradually administering small amounts of antivenin.
Newer kinds of antivenins derived from sheep are under study now and show some promise, according to FDA officials. But progress has been slow due to low demand and the small number of venomous bites a year. Certain venomous snakebites may be treated without using antivenin. This is usually a judgment call the doctor makes based on the snake's size and other factors, which normally involves close monitoring of patients in a medical facility.
"In some areas, such as desert areas, most rattlesnakes are small and don't have as potent a venom," says Edward L. Hall, M.D., a Thomasville, Ga., trauma surgeon who treats snakebites. "You might get by with those patients in not using antivenin." But with other snakes, Hall says, antivenin can be a lifesaver. For example, the Eastern diamondback rattlesnake--found in large quantities in the region of Georgia where Hall practices medicine and in other Southern states from the Carolinas to Louisiana--can reach six feet in length and deliver a potent payload of venom. "It's an enormously dangerous bite that requires very aggressive treatment [with antivenin] or the patient will die," Hall says.
Treatment Dilemmas
Because not all snakebites, including those from the same species, are equally dangerous, doctors sometimes face a dilemma over whether or not to administer antivenin. Venomous snakes, even dangerous ones like the Eastern diamondback, don't always release venom when they bite. Other snakes may release too small an amount to pose a hazard.Hall says his experience in Georgia bears this out. "Some 20 to 30 percent of patients we see who have been bitten by a snake, who actually have fang marks, have not received any venom at all." He says one reason for this may be poor timing by the snake. "Pit vipers have a very sophisticated mechanism that allows them to deliver venom at the exact instant the teeth are sunk into the flesh. So it has to be precise timing. But what we often see is that the [snake's timing is off and] venom is squirted on the pants leg or released prematurely."
Another complicating factor is the diverse potency of venom. "Venom can vary within species and even within litter mates--brothers and sisters," says Arizona physician Hardy. For example, he says, a common pit viper in the Southwest, the Mojave rattlesnake, may carry a powerful neurotoxic venom in some areas and a less toxic one in others.
Hall's work in Georgia and Florida shows that factors such as genetic differences among snakes, their age, nutritional status, and the time of year also can affect venom potency. All these variables make it nearly impossible for doctors to characterize a "typical" venomous snakebite. That's why there exists what Hall calls "so much controversy" about snakebite treatment.
The solution, Hall says, lies with the patient. "Truly the only way to look at snakebites is on an individual basis and on the patient's actual reaction to the venom." Basic signs like pain, swelling and bleeding, along with more complicated reactions such as ecchymosis (purple discoloration), necrosis (tissue dies and turns black), low blood pressure, and tingling of lips and tongue give medical professionals clues to the seriousness of bites and what treatment route they should take.
Some experts emphasize that though antivenin can effectively reverse the effects of venom and save life and limb, there is no guarantee that it can reverse damage already done, such as necrosis. Some patients may later require skin grafts or other treatment. Arizona physician Hardy says the potential for limiting complications is one compelling reason to seek medical treatment as soon as possible after a snakebite.
