Feb. 9, 2004 (San Diego) -- Stroke experts say "time is brain," meaning that once stroke occurs each ticking of the clock makes permanent damage more likely. But an experimental drug developed from a mainstay of horror stories -- vampire bats -- appears capable of beating the deadly stroke clock.
The new drug is called desmoteplase and it takes its name from Desmodus rotundus, the scientific name for vampire bats. When a bat bites its victim, a component of the bat's saliva keeps the victim's blood flowing without clots forming. The new drug is a genetically engineered version of the bat-saliva clot buster.
Steven Warach, MD, PhD, chief of the section on stroke diagnostics and therapeutics at the National Institute of Neurological Disorders and Stroke (NINDS), tells WebMD early studies of desmoteplase suggest that the drug can reverse stroke symptoms including difficulty in speaking and paralysis in 60% of patients treated with the highest test dose of the drug. Warach and colleagues conducted dose and safety studies of the drug in 43 stroke patients. He presented the results at the 29th International Stroke Conference here.
Moreover, the drug is effective up to nine hours after stroke onset, which is three times as long as the three-hour treatment window of the currently available clot-busting drug, tPA.
This type of stroke, which is called an ischemic stroke, accounts for 88% of the 700,000 new strokes diagnosed in the United States each year.
Warach says desmoteplase differs in a number of ways from tPA, including the possibility that it can dissolve a clot without increasing the risk of bleeding in other areas of the body -- especially in other regions of the brain, which is a well-recognized risk with tPA.
Warach's study did more than just test doses of a new -- and potentially breakout -- drug, it also tested a new method for identifying patients who could benefit from clot-busting treatment. He says that in the 10 years since the FDA approve tPA, stroke experts have been frustrated by the fact that tPA does not work in all patients. Estimates are that only about one in eight patients actually benefit. "So patient selection is extremely important," he says.
In this study, patients were selected using a new magnetic resonance imaging (MRI) technique called diffusion-perfusion mismatch. The technique can show the area of brain damage that cannot be reversed and the area that is not yet damaged but is at risk hours after the stroke.
Warach says patients with at least 20% of brain cells in the "at-risk" area are good candidates for treatment, but "the larger the at-risk area, the better the results." Asked if the same technique could be used to select patients for tPA, Warach said, "in my opinion, yes."
By repeating MRI scans after treatment with the new clot buster, the researchers were able to show that treatment restored blood flow. The return of blood flow, to areas considered to be at risk for irreversible damage, correlated with how well stroke victims did after treatment.
Howard Rowley MD, associate professor of radiology at the University of Wisconsin Medical School and lead radiologist for the study, says the "new MRI techniques are key in helping to select the right patients for therapy."
Rowley also says that the impact of the expanded treatment window -- 9 hours vs. 3 hours -- "cannot be overstated. Buying more time to treat stroke symptoms -- and the ability to safely restore blood flow to the brain -- means we can give acute stroke victims hope for a better outcome, even if having a stroke cannot be prevented."
Michael Moskowitz, MD, director of the stroke and neurovascular regulation laboratory at Harvard Medical School, says the "three hour window is pretty severe when we are trying to get patients to treatment." He tells WebMD that a drug that can be used "as late as nine hours is extremely promising."
Moskowitz, who led a news conference where Warach presented the results, was not involved in the study.