A drug for heavy metal poisoning may double as a snakebite treatment

An old drug may find new use as a speedy treatment for venomous snakebites.

The drug, called unithiol, has long been used as a therapy for heavy metal poisoning. Research in mice suggests the drug could block damaging proteins that are found in the venom of many vipers. A recent Phase I clinical trial explored different dosages of the drug in people — larger quantities than are used for metal poisoning — and didn’t find safety issues, researchers report in the March eBioMedicine.

The World Health Organization considers venomous snakebites a priority neglected tropical disease, with people in the rural tropics especially vulnerable. An estimated 1.2 million to 5.5 million people suffer venomous snakebites annually, with more than 125,000 dying from the bites and three to four times that number left with disabilities such as the loss of limbs to amputation.

The venoms of vipers found in Asia, Africa, North America and South America contain proteins called metalloproteinase enzymes. These proteins cause profuse bleeding and tissue damage and need zinc from the body of the bitten to do their job.

Enter unithiol, which can block the proteins by mopping up that zinc. The drug can be given orally and is stable at room temperature, opening up the possibility of easy availability in rural areas. That’s needed because a delay in the treatment of venomous snakebites increases the risk of disability and death.

Right now, antivenoms are the only effective treatment for the bites. But venoms vary, and most need their own specific antivenoms, which are made by raising antibodies in large mammals that have been injected with a particular venom. The medicines are expensive and aren’t usually available outside of health care facilities because they are administered intravenously and can cause severe allergic reactions. This can mean long travel times for people in remote areas.

It’s not known yet what dose of unithiol might work for venomous snakebites in people, so the Phase I clinical trial assessed a variety of doses in 64 adults in Kenya. The researchers established a three-dose regimen to test against bites in future trials.

Unithiol might serve as an alternative to antivenom or be useful as an initial treatment to keep damage in check until a person can get to a hospital for antivenom, the researchers write.