Nitric oxide cream as snake bite first aid may buy time: Study

By Dr. Ananya Mandal, MDJun 28 2011

According to Australian scientists working on snake bits, a chemical compound that is used on heart patients may raise chances of survival for snakebite victim.

The study was published in Nature Medicine on Monday where researchers said the chemical nitric oxide can slow down by as much as 50 percent the time it takes for snake venom to enter the bloodstream. With that extra time, victims can seek medical help, said lead author Dirk van Helden, Associate professor at the School of Biomedical Sciences, University of Newcastle in Australia.

Helden said, “When you are bitten by a snake, the toxins are large molecules and they get injected into tissues. They can't break into blood vessels because they are too big. So they get taken up by the lymphatic system and it takes them into the blood vessels… The idea is to close off the lymph flow ... and we tried it and it markedly slowed lymph flow in rats and also in humans.”

The team rubbed an ointment containing nitric oxide around the spot where mice were injected with lethal doses of snake venom and found that it slowed lymph flow significantly. He explained, “(They) lived for an hour on average (without ointment), but when we put the cream on, (another group of mice) lived for 90 minutes. If you can slow the lymph, it has a massive effect on survival.”

To test the treatment, fifteen human volunteers were injected on the top of the foot, with a traceable non-toxic substance that is physically similar to snake venom. The ointment had the same effect on human volunteers, although in this case, the participants were injected with a harmless dye which had molecules of roughly the same size as snake venom. The researchers used a special camera to measure how long it took for the mock venom to travel from the foot to the groin. Then, on a separate occasion, they repeated the experiment with the addition of a 5 centimetre patch of glycerol-nitrate-containing ointment next to the injection site. This was applied within a minute of the injection. “Transit time to the groin was three-fold greater when we applied the ointment,” explained van Helden.

Co-author Professor Geoffrey Isbister said there are approximately 3000 humans with suspected snakebites each year in Australia. “There may be more, but it's always difficult to estimate. [Of these, there are] about 100 to 200 severe envenomings and one to four deaths,” he said. Each year, snakebite accounts for an estimated 100,000 deaths and 400,000 amputations worldwide, mostly in South Asia, southeast Asia and sub-Saharan Africa because anti-venom is not readily available. Australia is home to some of the world's most venomous snakes.

Associate Professor Julian White of the Women's and Children's Hospital in Adelaide believes this new approach may be a useful adjunct to existing treatments, which include immobilisation and pressure bandages. He says that it needs further evaluation and validation before it can be recommended. “The problem with all first aid treatments is that it is very hard to properly test to see whether the treatments work in real cases ... and with snakebites you don't have lots of patients presenting in a controlled setting. [But] looking for new methods to make things better is a very worthwhile enterprise ... from my point of view, as a clinical toxicologist, I'd be saying to people watch this space keenly,” he said.