(McClatchy-Tribune Information Services) -- The American Heart Association has issued an advisory extending the use of a "clot-busting" drug.

The advisory means that patients who show up at emergency rooms will have an extra 90 minutes in which to receive medication that could save their lives or preserve their ability to function.

For more than a decade, the U.S. Food and Drug Administration set a limit on administering the clot-dissolving drug at 3 hours after a patient suffers a stroke.

But last month, the Heart Association's advisory said the drug, "recombinant tissue-plasminogen activator," or rt-PA, can be used up to 4.5 hours after the beginning of symptoms of a stroke caused by a blood clot.

A panel from the American Heart and American Stroke associations looked at studies that showed some people could use the drug after the 3-hour window closed, said Dr. Colin P. Derdeyn, professor of radiology, neurology and neurological surgery at Washington University School of Medicine.

Derdeyn was a member of the panel that issued the new advisory.

The drug works by almost instantly dissolving clots, which account for more than 85 percent of strokes. It doesn't help when strokes are caused by a burst blood vessel in the brain..

When someone arrives at an emergency room, tests to pinpoint the cause of a stroke may take 45 minutes, Derdeyn said, enough time to perhaps preclude using the drug.

"But we've used it past the 3-hour limit with success," Derdeyn said. Barnes-Jewish has been using the 4.5-hour window for a while, he said.

People who aren't suited for use of the drug after 3 hours are those who are older than 80, on blood thinner for a cardiovascular condition, have diabetes or have had previous strokes.

Barnes-Jewish Hospital gets about 1,200 stroke patients a year, a hospital spokesperson said. Of those, about 40 on average receive the clot-dissolving drug. Since using the wider window at the beginning of this year, four patients have been given the drug between 3 and 4.5 hours after symptoms.

Meanwhile, the advisory unties the hands of doctors who choose to follow the stricter protocols laid out by the drug's label, said Dr. Nirav Vora, a professor of neurology at St. Louis University School of Medicine and head of the stroke program at DePaul Health Center.

While off-label use of a drug is legal once the FDA allows a drug on the market, "It was somewhat of a legal matter," Vora said. "Now if (physicians) wish to use it, there's support from the studies and the (Heart Association).

The Heart Association advisory bases its findings on re-examination of studies done in Europe and the United States that date to the early 1990s when the drug was being tested.

Early tests showed the drug didn't work after 3 hours. But researchers later found that certain people responded to treatment after that point.

Krysta Pellegrino, of Genentech corporate relations, said that with the Heart Association advisory and the strength of the European and American studies used by the Heart Association, the company will seek approval from the U.S. Food and Drug Administration to update the label so that it reflects the 4.5-hour extension.

The Heart Association says the challenge remains getting people to emergency rooms in time.

Fewer than 25 percent of stoke victims recognize their symptoms soon enough.

"That's what we're doing now, to get the word out," says Madelyn Alexander, communications director for the Heart Association's St. Louis office.

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