Time is the foe for people who have been bitten by a poisonous snake, but a new study may give them a bit more of it. Researchers have identified an ointment that slows the spread of some kinds of snake venom through the body, potentially giving snakebite victims longer to reach a hospital or clinic.
Although poisonous snakes kill only a handful of people in the United States each year, the World Health Organization puts the global toll at about 100,000 people. When some snakes strike, the bulky proteins in their venom don't infiltrate the bloodstream immediately but wend through the lymphatic system to the heart. In Australia, a country slithering with noxious snakes, the recommended first aid for a bite includes tightly wrapping the bitten limb to shut the lymphatic vessels—a method called pressure bandage with immobilization (PBI). The idea is to hamper the venom's spread until the victim can receive antivenom medicine, essentially antibodies that lock onto and neutralize the poison. But PBI is not practical if the bite is on the torso or face, and one study found that even people trained to perform the technique do it right only about half the time. As a result, some people don't get antivenom in time.
So physiologist Dirk van Helden of the University of Newcastle in Australia and colleagues went looking for a chemical method to detain the venom. They settled on an ointment that contains glyceryl trinitrate, the compound better known as nitroglycerin that doctors have used to treat everything from tennis elbow to angina. The ointment, prescribed for a painful condition called anal fissures, releases nitric oxide, causing the lymphatic vessels to clench. The researchers first injected volunteers in the foot with a harmless radioactive mixture that, like some snake toxins, moves through the lymphatic vessels. In control subjects that didn't receive the ointment, the mixture took 13 minutes to climb to the top of the leg. But it required 54 minutes if the researchers immediately smeared the ointment around the injection site, the team reports online today in Nature Medicine.
To determine whether the ointment improved survival, the researchers injected the feet of anesthetized rats with venom from the eastern brown snake, a cobra relative that is one of Australia's deadliest, and measured how much time elapsed before the rodents stopped breathing. Rats lived about 50% longer if the researchers slathered the rodents' hind limbs with the cream .
Although the team can't specify how many minutes or hours the treatment might buy, the findings suggest that "it gives you time and a half to get help," says van Helden. "I'd prefer that to just time." He says that hikers and people who work in rural areas might consider carrying the cream in case they get bitten when they are far from medical facilities.
The method is "very exciting," says Steven Seifert, medical director of the New Mexico Poison and Drug Information Center in Albuquerque. "It makes sense to try to slow the passage of the venom into the circulation." Medical toxicologist Eric Lavonas, associate director of the Rocky Mountain Poison and Drug Center in Denver, Colorado, is also impressed. "This is really promising," he says. The authors "did the right studies to evaluate this approach."
Still, Seifert and Lavonas question whether such a treatment would do much good in the United States. Australian snakes largely inject neurotoxic venom that spreads through the body and attacks the nervous system, triggering paralysis. The perpetrators of most U.S. snakebites are rattlesnakes, copperheads, and cottonmouths, which inject a different type of venom that mainly destroys the tissue near the bite. But the researchers note that the ointment could prove valuable in many other countries inhabited by dangerous snakes, such as cobras, mambas, and kraits, that produce neurotoxic venom. "If this treatment pans out, it may revolutionize first aid for snakebite in parts of the world where venom causes paralysis," Lavonas says.