WEDNESDAY, Feb. 1 (HealthDay News) -- New research suggests that it may be safe to give the clot-busting drug tPA to people who wake up with stroke symptoms, even though there is a short time window in which to use the treatment and doctors have no idea when these patients first started experiencing their stroke.

The powerful medication can save lives and stave off lasting disability after a stroke, but experts believe it needs to be given within 4.5 hours of the start of symptoms. Almost 25 percent of people who have strokes have them while they are asleep, the study authors noted, and doctors typically err on the side of caution, assume the stroke happened when the patient first went to bed and do not treat with tPA.

However, in this latest study, doctors from King's College Hospital in London used a stroke registry to compare 326 patients treated with tPA within 4.5 hours of symptoms to 68 "wake-up" stroke patients. The second group only received clot-busting drugs if they had similar symptoms and showed the same signs of early stroke-related brain changes on CT scans that people whose strokes occurred within the 4.5-hour window did. The risks, namely bleeding, of giving tPA outside of this window are thought to outweigh its benefits.

In the study, the death rates, risk of bleeding inside the brain and recovery rates after three months were similar in both groups of stroke patients.

"Our study shows that administering clot-busting drugs to patients with wake-up stroke who have the same clinical and imaging features as those treated within current guidelines is feasible and safe," study author Dr. Dulka Manawadu, a medical consultant at King's College Hospital, said in a news release, although he added that more research is needed to confirm the findings.

The study was slated to be presented Wednesday at the American Stroke Association meeting in New Orleans. Research presented at medical meetings should be viewed as preliminary until published in a peer-reviewed medical journal.

Of the similar findings between groups,"it is encouraging and it doesn't yet prove that they will get the same benefits, but it doesn't seem that the risk is excessive," said Dr. Steven Greenberg, vice chairman of the International Stroke Conference 2012's program committee and a professor of neurology at Harvard Medical School. "Even if only a subset of wake-up stroke patients were eligible for tPA, it is still a subset of a substantially large number, so the importance is pretty high."

The bottom line remains unchanged, he said: "If you or someone you know is having a stroke, call 911 or get to an emergency room as fast as possible. The earlier treatment is started within the 4.5-hour window, the better. With every minute that goes by, you lose part of the benefit and gain more risk."

"A large number of patients can't receive tPA is because they are too far past the window of opportunity," added Dr. M. Shazam Hussain, a neurologist at the Cleveland Clinic, in Ohio. Most "wake-up" strokes do occur close to when a person wakes up, he noted, so "potentially this will expand treatment quite significantly."

"A lot of people are denied treatment because there is no exact time of onset, because the risks may outweigh the benefits of tPA," he said. "I want to see a larger study done, but it certainly lends weight to help advocate for expanded use of tPA among wake-up stroke patients."

More information

Find out about stroke warning signs at the American Stroke Association.