Model illustrates the position of a blocked artery in stroke. (CBC)

Stroke patients can safely be given a clot dissolving drug within 4.5 hours, an extension of the conventional three-hour window, a European study suggests. The longer timeframe may help patients who can't reach a hospital quickly to access specialist care.

An ischemic stroke occurs when a clot blocks a blood vessel in the brain and cuts off circulation, potentially causing death or permanent disability. Doctors give a drug called tissue plasminogen activator or tPA by intravenous to dissolve clogs lodged in the brain to treat the most common type of stroke.

Treatment guidelines in Canada, the U.S. and Europe set a three-hour time limit for giving tPA because of fears that it may cause dangerous bleeding or other complications.

Given safety concerns, European regulators requested further observational studies and a randomized clinical trial on tPA, also called alteplase.

In Monday's online issue of the medical journal The Lancet, Prof. Nils Wahlgren of the department of clinical neurosciences at Karolinska University Hospital in Stockholm and his colleagues reported no significant differences between subjects who were given the drug after three hours compared to four hours.

"Alteplase remains safe when given at 3–4.5 h after ischemic stroke, offering an opportunity for patients who cannot be treated within the standard three-hour timeframe," the researchers concluded in the journal.

"Our findings lend support to those of the meta-analysis suggesting a potentially longer timeframe for intravenous [use of tPA] of 4.5 hours."

Too soon for guideline changes

The researchers compared 664 people who had the drug between three and 4.5 hours after a stroke and nearly 12,000 who received tPA within three hours.

The death rate among the three-hour group was 12.7 per cent, versus 12.2 per cent for those who got the drug later, the researchers reported.

Functional independence, or that ability to act independently, was 58 per cent in the early group compared to 56.3 per cent in those who got the drug later.

Rates of brain haemorrhage were also similar, at 2.2 per cent in those who got tPA earlier compared with 1.6 per cent in the others.

The researchers are planning to present the observational results at an international meeting in Stockholm in November.

Before changing stroke treatment guidelines, neurologists will consider the results of randomized control trials that are underway. As with heart attacks, it remains true that the sooner blood supply is restored to the brain, the better.

"Extension of the timeframe of systemic thrombolysis seems to be a safe option for patients with acute stroke," Dr. Andrei Alexandrov of the Comprehensive Stroke Center at University of Alabama at Birmingham Hospital wrote in a journal commentary accompanying the study.

"We are looking forward to moving away from rigid timeframes to treatment based on imaging that can assess brain pathophysiology and tissue viability," wrote Alexandrov and Dr. Georgios Tsivgoulis of the department of neurology at University Hospital of Alexandroupolis in Greece.

Alexandrov also noted that half of those treated late received tPA just 15 minutes after the end of the three-hour limit.

Patients treated later were also three years younger on average, had slightly less severe neurological deficits before treatment, and had lower rates of hypertension and high cholesterol than those treated within three hours.