Stroke sufferers can still benefit from the TPA clot buster even if they receive it up to 90 minutes beyond the current three-hour window following the start of symptoms, according to a study in The New England Journal of Medicine.

The finding could potentially extend treatment to thousands more people each year and prevent many from being left disabled, the Associated Press notes. However, the results do not change long-standing advice that stroke victims seek immediate help.

The study found the drug could safely be given up to 4½ hours after the start of symptoms. TPA is marketed by Boehringer Ingelheim, which funded the study, as Actilyse overseas and the med is sold in the US and Canada by Genentech as Activase. Here is the abstract.

The best treatment is giving patients TPA to break up a clot and open the artery. A large federal study in 1995 showed that it could save lives when given within three hours of the start of a stroke. But only a third of stroke victims seek help that fast, and fewer than 5 percent get TPA now. Some doctors have been trying to push the time limit, and the new study is the largest to test the approach.

Doctors randomly assigned 821 stroke patients in Europe who were not treated within three hours to receive an intravenous dose of TPA or a dummy drug up to 4½ hours after symptoms started.

Doctors found those given TPA fared better - 52 percent survived without major disability compared with 45 percent of the others. The drug group had more cases of bleeding in the brain - 27 percent versus 18 percent. However, it was serious in only about 2 percent. The death rate was similar in both groups.

“I strongly believe it has the potential to have a major impact on practice,” Lee Schwamm, director of Massachusetts General Hospital’s acute stroke program, tells the AP, while estimating that nearly 20,000 more patients a year could be treated under the time extension

Some experts worry that some patients and doctors may take their time treating strokes given the extra window. “It is very clear that our focus must remain on the door-to-needle time. Every minute matters during a stroke,” Patrick Lyden, head of the University of California, San Diego stroke center, wrote in an accompanying editorial.

Stroke neurologist Walter Koroshetz of the National Institutes of Health tells the AP that treatment guidelines deserve a fresh look “to try to break this three-hour barrier.” He adds that it’s not clear which patients might benefit most from the extra time. Since the European study focused on mild stroke cases, it’s unknown if severe stroke victims would also benefit.

Ken Gaines, stroke director at New Orlean’s Ochsner Medical Center, might be more willing to consider giving TPA in borderline cases, but he remains concerned about bleeding side effects. “The real solution is to move faster,” he tells the AP. “There is diminishing return the longer you delay treatment.”