Vampire spit gives strokes a licking.

An experimental drug derived from the saliva of vampire bats can clear away blood clots in the brains of stroke patients and restore blood flow to brain areas starved of circulation. The findings come from a small number of people but have paved the way for a large trial of the novel drug, called desmoteplase, later this year.

Most strokes result from clots, but only about 1 in 20 patients receives the sole clot-dissolving drug approved for treating stroke, tissue plasminogen activator (tPA). That's because most stroke victims get to a hospital more than 3 hours after they're stricken. By then, risk of hemorrhage from a dose of tPA outweighs the drug's potential benefits.

Desmoteplase could give doctors and patients a health-preserving alternative. In previous tests on animals (SN: 1/18/03, p. 37) and in a handful of people, desmoteplase was safe to give up to 9 hours after a stroke.

In the new study, neurologist Anthony Furlan of the Cleveland Clinic and his coworkers gave 37 people infusions of either an inert substance or desmoteplase between 3 and 9 hours after a stroke. Some people got larger doses of the drug than others.

The lower dosage of desmoteplase was no more effective than the placebo, Furlan says. However, compared with people getting the placebo, significantly more patients receiving the higher dose of desmoteplase had restored circulation in blood-starved parts of their brains.

Even though patients receiving desmoteplase got the drug an average 7 hours after a stroke, none hemorrhaged, Furlan says.

Restoration of blood flow to the affected brain areas correlated with better scores on subsequent assessments of people's disability levels. Desmoteplase is made by Paion of Aachen, Germany.