Covering a snakebite wound with an ointment that slows the spread of the snake venom through the body’s lymphatic system could delay the toxin from entering the bloodstream and give snakebite victims more precious time to seek medical help.
In some snake venoms, the toxins are too large to immediately enter the bloodstream and instead first travel through the lymphatic system before entering the heart. As nitric oxide inhibits the pumping action of the body’s lymph system, Megan Saul and colleagues reasoned that applying topical agents that release nitric oxide to the snakebite wound could impede the venom’s progress in the body. Thus, the researchers tested an ointment that contained nitric-oxide-releasing glyceryl trinitrate in their study published in Nature Medicine.
By simulating a snakebite in human volunteers (6 men and 9 women, who were told to remain still throughout the experiment, an important component of snake bite first aid) and injecting participants with a molecular dye, the researchers could track the progress of ‘snake venom’ through the lymph (from the initial ‘bite’ site in the foot to the lymph nodes in the groin). Applying a thick layer of the ointment within 1 minute of the injection markedly increased the foot-to-groin lymph transit time of the dye by nearly fourfold, from 13 min without treatment to 54 min with the ointment. Similarly, using the same principle in rats, the ointment also increased lymph transit time by threefold (from 3.2 min to 9.4 min). The researchers then went on to test whether the ointment could improve survival in rats injected with snake venom (from the Eastern Brown snake, one ofAustralia’s most deadly) and measured how time it took before the animals stopped breathing. Crucially, rats treated with the ointment lived about 50% longer (time to respiratory rest was 65 min in controls and 96 min in treated rats).
Pressure bandages and pads can be used to mechanically block the flow of snake venom in the body, but this approach can’t be used on bites to the face or torso and can be difficult to perform properly. Arguably, carrying a cream with you when out hiking in the wild is a simple new addition to your first aid kit and a bonus is that the ointment used in the study (Rectogesic, Care Pharmaceuticals) is already commercially available, albeit as a treatment for anal fistulas. Even though we don’t know exactly how much additional time this ointment will buy in bitten humans, that extra time could prove vital when seeking suitable antivenom treatment, especially in those in which pressure immobilisation is not possible.
Megan E Saul, Paul A Thomas, Peter J Dosen, Geoffrey K Isbister, Margaret A O’Leary, Ian M Whyte, Sally A McFadden &, & Dirk F van Helden (2011). A pharmacological approach to first aid treatment for snakebite Nature Medicine : doi:10.1038/nm.2382