updated 2/7/2004 5:48:24 PM ET 2004-02-07T22:48:24

Considering the lack of good treatments for strokes, it probably is no surprise that researchers will consider just about anything. But still, vampire bat saliva?

New data released Saturday suggest that idea, farfetched as it sounds, actually may work.

Doctors would like to quickly dissolve the clots in brain arteries that cause about 80 percent of all strokes, the third leading cause of death behind heart disease and cancer. But their only widely available treatment, a bioengineered human protein called TPA, has drawbacks and is given to only about 5 percent of U.S. stroke victims.

If used improperly, the drug can trigger disastrous bleeding. One of its chief limitations is that it must be given within three hours of the start of stroke symptoms. Many victims, hoping their symptoms will go away, do not get to the hospital quickly enough.

So, in search of something better, researchers have been experimenting with another natural anticlotting substance, the saliva of Desmodus rotundus, the vampire bat. The hope is that the active protein, called desmoteplase, will be more precisely targeted at clots and can be used several hours longer after symptoms begin.

In theory, desmoteplase may break up blood clots in the brain without affecting the rest of the body’s clotting system and with less risk of hemorrhaging inside the head.

Certainly, it works for the bat, a one-ounce, grayish-brown creature that ranges over Central and South America and preys mostly on livestock. The protein keeps its victims’ blood flowing clot-free so it can feed.

'Promising' new therapy
In the first of two mid-size studies on the approach, doctors in Europe, Australia and Asia randomly gave either a genetically engineered version of the saliva protein or dummy injections to 104 stroke victims. All had suffered their strokes within the previous three to nine hours.

Dr. Steven Warach, chief of stroke therapy at the National Institute of Neurological Diseases and Stroke, presented the results at a meeting of the American Stroke Association in San Diego.

The researchers tested several different doses. Sixty percent of those getting the largest amount had an excellent recovery after three months, compared with 22 percent in the untreated comparison group.

“This is a promising new stroke therapy,” he said.

The study was sponsored by Paion, a German company developing desmoteplase. A similar study, still under way, is expected to enroll more than 100 patients at 17 hospitals in the United States. Already being planned is a much larger study intended to prove the drug’s safety and effectiveness.

“These are very important results, because they suggest that with a different drug we can extend the therapeutic window from three hours, which is pretty severe when trying to get patients to treatment,” said Dr. Michael Moskowitz of Massachusetts General Hospital.

Doctors were especially impressed that only one patient getting the saliva protein suffered brain bleeding.

“It’s very good that bleeding is not occurring,” said Dr. Daniel Hanley of Johns Hopkins University. “That, of course, will require further study to be sure.”

The researchers gave MRI scans and limited treatment to patients who had significant amounts of brain tissue that was at risk of dying but still was potentially salvageable. Warach said about half of all stroke patients seen after three hours fit this criteria.

“There are patients we can help after three hours and maybe even after nine hours,” Warach said.

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