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New use for old drug

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It is estimated that almost 5 million people are bitten by snakes each year with up to 125,000 deaths as a result. The majority of snakebite victims live in impoverished, rural areas with limited medical resources. Survivors may suffer permanent disability even after successful treatment the cost of which can cause economic ruin for them and their families. Yet snakebite has been one of the most neglected of all tropical diseases.

The venom of cobras and many other snakes contain neurotoxins which work by blocking the neurotransmitter acetylcholine resulting in symptoms that typically progress from eye muscle weakness to paralysis and death by respiratory failure. The standard treatment for neurotoxic snakebite is an appropriate antivenom with or without neostigmine both of which are administered by injection. Neostigmine cannot deactivate the venom directly but it can allow what little acetylcholine is available to move freely. It can buy time in an emergency. Efforts to produce a universal antivenom have proved difficult since venoms can be very different even in closely related species of snakes. And there are said to be over 500 species of venomous snakes worldwide. 

Following the death from snakebite of one of their scientists while working in the jungles of Myanmar a few years ago, the California Academy of Sciences brought in Matthew Lewin, a doctor and expert in wilderness medicine. He developed highly mobile and effective first-aid kits, which included intravenous neostigmine, to be taken into remote jungles and deserts.

Noting that administering intravenous drugs outside hospital can be difficult and that probably over 75% of snakebite deaths occur even before reaching a hospital, a team led by Lewin with Stephen Samuel from Trinity College, Dublin, formulated neostigmine as a nasal spray. A report in the Journal of Tropical Medicine describes how tests on mice injected with high doses of Indian cobra venom gave encouraging results so a healthy human volunteer was paralysed, while awake, using a toxin that mimics the effect of neurotoxic venom. The patient recovered within 20 minutes of administering neostigmine nasal spray. Other tests were carried out successfully on snakebite victims in a hospital in Tamil Nadu, India.

Lewin calls it ironic that virtually every medical organisation has a snake on its emblem but no ability to treat snakebite in the field. Although neostigmine nasal spray may not be the desired universal antidote, it could make a profound difference in the health of millions of people.

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From: Beyond pharmacy blog

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