Blood-thinning drug heparin may stop snakebite victims losing limbs

A commonly used blood thinner could prevent hundreds of thousands of people from needing amputations after a cobra bite.

Snakebites kill up to 138,000 people each year, mostly in sub-Saharan Africa and South and South-East Asia. Another 400,000 people have complications, such as the death of body tissues and subsequent amputations.

Focusing on complications from cobra bites, Tian Du at the University of Sydney, Australia, and her team found that the venom targets a molecule called heparan sulfate, which lines the surface of cells at the site of the bite, and a naturally occurring substance called heparin, which is produced by certain immune cells.

Next, the researchers exposed human skin and blood cells to the venom of two cobra species from Africa: the red spitting cobra (Naja pallida) and the black-necked spitting cobra (Naja nigricollis). Adding heparin, which is commonly administered as a drug to thin blood, prevented the toxins from killing the cells.

Similar experiments in mice also reduced the risk of tissue death. In mice, heparin “could almost completely block the local damage at the bite site”, says team member Greg Neely, also at the University of Sydney.

The scientists think the treatment could be effective for bites from many different types of cobras but is unlikely to work on non-cobra species, unless their toxins use a similar chemical pathway to destroy cells.

Unlike existing antivenoms, heparin is stable at room temperature, which could improve access when prompt treatment is needed, says Du. This could be done via an auto-injector, such as an EpiPen, she says.

Another advantage of heparin is that existing antivenoms don’t prevent necrosis, says Du. However, Geoff Isbister at the University of Newcastle in Australia says that is probably because they are not generally available immediately after a snakebite.

“What they didn’t do in this article was compare this to antivenom, because it is highly likely that antivenom would be just as effective,” he says. The mice were given heparin immediately, which may have been why it was effective, says Isbister. “But will it work after 1 hour, 4 hours or [the] 24 hours that it takes to get from a remote location in Tanzania to a person bitten by a cobra?”