DALLAS (AP) -- A change to stroke treatment guidelines is expanding the time that some patients can get clot-busting drugs. Current recommendations limit the use of the medicine to within three hours after the start of stroke symptoms. That treatment window is now being lengthened to 4 1/2 hours for some patients.

But the committee that made the change stressed that the earlier the treatment, the better for stroke victims.

"They should call the ambulance straight away and get moving," said Dr. Gregory del Zoppo, of the University of Washington School of Medicine in Seattle, who headed the committee for the American Heart Association Stroke Council.

The update, published online Thursday in the heart group's journal Stroke, comes after a European study last fall found stroke sufferers still benefited from getting the medicine an hour or so beyond the three-hour window.

The new guideline is expected to increase the number of people who get the treatment. Only about a third of stroke sufferers get help within three hours, and only about 5 percent get the drug now. Many people don't recognize the signs of a stroke: numbness or weakness in the face, arm or leg; trouble speaking, seeing or walking; a sudden, severe headache.

Stroke is the third leading cause of death in the U.S., with about 795,000 people suffering a new or recurrent stroke each year and more than 140,000 people dying. Strokes caused by blood clots are the most common; the clot blocks an artery supplying blood to the brain, which starves brain cells of oxygen. The drug TPA breaks up the clot and opens the artery.

Another member of the committee, Dr. Jeffrey Saver, of the University of California at Los Angeles, said some hospitals extended the time for using the clot dissolver after the European study, while many have been waiting for national guidelines.

He said the change could increase the number of people who get the drug by a third, to 7 or 8 percent of stroke victims.

Dr. Mark D. Johnson, a stroke specialist at the University of Texas Southwestern Medical Center in Dallas, said that the expanded time frame is good news but the emphasis is still on getting treatment sooner rather than later.

"If you were to arrive in 30 minutes, the chances of a better outcome are higher than if you arrive in four hours," said Johnson.

The new guideline notes that some patients should still be restricted to treatment within the three-hour period: people older than 80, those suffering from a severe stroke or with a history of stroke and diabetes or those taking anti-clotting drugs.

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