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Salve buys time after snakebite: ointment slows venom's progress to vital organs.

Indiana Jones, intrepid cinematic archaeologist, is famously afraid of snakes. Perhaps he wouldn't need to be if he had an ointment recently tested by scientists in Australia. Quickly applying a nitric oxide-producing ointment near the bite site slows the spread of some venoms, including the notorious eastern brown snake's, the researchers report online June 26 in Nature Medicine.

"This treatment might make all the difference between dying on the road and getting to the hospital in time," says physician and tropical medicine specialist David Warrell of the University of Oxford, who was not involved with the study. Worldwide, snakebites cause about 100,000 deaths and 400,000 limb amputations each year.


Physiologist Dirk van Helden at the University of Newcastle in Australia and his colleagues showed that, in humans, applying a nitric oxide-producing ointment within one minute of a simulated snakebite slows the transit of injected tracer molecules. Foot-to-groin tracer travel times increased from an average of 13 minutes without the ointment to an average of 54 minutes with the ointment, when applied in a 5-centimeter-diameter circle just up the limb from the bite site.

The group also tested the effects of the cream on rats injected with venom from the eastern brown snake (Pseudonaja textilis), native to Australia. In rats slathered with ointment, symptoms of snakebite toxicity set in about 96 minutes after injection, compared with about 65 minutes in untreated animals.

The nitric oxide source in the ointment is nitroglycerin, the same compound used to treat angina. When applied to the body, the ointment releases microscopic amounts of nitric oxide gas, which sinks through the skin.

There, the gas inhibits pumping of the lymphatic vessels--the primary roadways for molecules too big to squeeze through blood vessel walls and hitch a ride in the bloodstream.

But victims might be out of luck if bitten by a black mamba or cobra, since the ointment isn't effective against venom containing smaller toxic proteins capable of directly entering the bloodstream.

Another potential snag is the need for bite victims to be quick on the draw. The scientists applied ointment within 20 seconds of a snakebite in rats and within a minute in the human tracer tests.

Van Helden hypothesizes that a combination of ointment and pressure treatment might be the best way to slow the spread of snake venom. But "if I had the ointment in mybackpack," he says, "that would be the first I'd put on."
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Title Annotation:Body & Brain
Author:Drake, Nadia
Publication:Science News
Geographic Code:8AUST
Date:Jul 30, 2011
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