Over the past few years researchers in Mexico have become global leaders in developing drugs to treat bites from poisonous spiders and snakes. Several of their remedies are clearing the hurdles of the U.S. Food and Drug Administration, including the scorpion antivenom Anascorp, which was approved by the FDA in 2011, and black widow drugs that are in advanced clinical trials.

Antivenoms are among the oldest drugs in the medical arsenal. They were first produced in the late 1800s at France's Pasteur Institute, and since the 1930s pharmaceutical company Merck has been manufacturing antivenom for black widow bites. But Merck limited distribution in 2009 because of side effects and poor drug sales, and compounds that counteract venom from scorpions and snakes have also been in short supply. The team at the National Autonomous University of Mexico, led by molecular biologist Alejandro Alagón, has introduced a new generation of antivenoms that are safer and less expensive to produce.

The method is based on the one scientists used in the 1800s: they inject venom into animals that have powerful natural defenses against the toxin. They then harvest and purify the antibodies, which are Y-shaped molecules that attach their forked end to the venom and neutralize it. In the case of antibodies directed against black widow bites, the molecule's tail (the bottom of the Y) can interact with the human body and occasionally cause a negative reaction—in a few cases, with fatal results. Although such side effects are rare, many physicians preferred not to use Merck's aging recipe. Black widow bites cause two days of crippling pain, but they do not usually kill, so doctors often treat just the symptoms.

Alagón and his team came up with a twist on the old formula: they chemically cut off the tail of the antivenom antibody, making the Y into a V to lower the risk of side effects. Alagón says the updated formula for black widow bites is safer than the old one and cheaper than a hospital stay—it can eliminate symptoms in 30 minutes.

Because the new antivenoms are relatively inexpensive to produce, Alagón's lab thinks the drugs may be affordable in Africa, where many pharmaceutical companies simply don't see a market for such products.

COMMENT AT ScientificAmerican.com/jan2013