24 February 2015

Aspirin 'resistance' may mean worse strokes

A daily dose of aspirin won't prevent blood clotting in about 28% of people, which may lead to more severe strokes.


People who are "resistant" to aspirin may be at risk for larger, more severe strokes, South Korean researchers report.

Drug prevents blood clots

Doctors often prescribe low-dose aspirin to people at high risk of stroke because the drug helps prevent blood clots. But for about 28 percent of stroke patients in a new study, aspirin didn't keep blood from clotting. And their strokes were worse than strokes suffered by aspirin-users who weren't resistant to the drug.

"Aspirin resistance is an important predictor of severe stroke and large stroke size in patients taking aspirin before having a stroke," said lead researcher Dr. Mi Sun Oh, of the department of neurology at Hallym University College of Medicine in Seoul.

What causes aspirin resistance isn't known. Other studies have found that between 5 percent and 45 percent of patients have this problem, but doctors do not routinely test for it.

Read: Stroke

Clots that break loose can travel to the brain and cause "ischemic" strokes – the most common type of stroke. This study suggests that people who are aspirin-resistant might need a different drug to prevent dangerous clotting, Oh said.

"In patients at high risk for stroke with aspirin resistance, different anti-clotting drugs – such as clopidogrel (Plavix) – can be considered as alternatives to prevent another stroke or decrease stroke severity," Oh said.

The findings of the study were released on 23 February, ahead of its official presentation in April at the annual meeting of the American Academy of Neurology in Washington, D.C. Data and conclusions presented at meetings are usually considered preliminary until published in a peer-reviewed medical journal.

Smaller and less severe strokes

Dr. Ralph Sacco, chairman of neurology at the University of Miami Miller School of Medicine, said the new research sheds light on the aspirin-stroke relationship. Prior studies have suggested that patients taking aspirin at the time of their stroke may have smaller and less severe strokes. This would indicate that these people aren't resistant to aspirin.

"This study fits with this premise," Sacco said.

Why this happens isn't known, he added.

"One way aspirin works is to prevent platelets [particles that form clots in the blood] from clumping, and this could mean that clots that are released and block brain arteries are smaller and lead to smaller areas of brain injury," Sacco speculated.

Read: Stroke - what to do in an emergency

"Although we do not routinely test for aspirin resistance, in the future era of targeted medicine we may improve the ability to assess whether someone is aspirin-resistant and choose medicines more accurately," he said.

For the study, Oh and colleagues studied 310 patients who had been taking aspirin for at least seven days before they suffered an ischemic stroke. Aspirin resistance was checked within 24 hours of hospital admission.

Research findings

The researchers found that nearly 28 percent of the patients were resistant to aspirin. Their strokes ranged from 3 to 11 on a stroke severity score, compared with scores of 1 to 6 among aspirin responders.

Read: Stents are best for removing stroke-causing blood clots

Moreover, strokes of patients resistant to aspirin affected about twice the brain area as the strokes of those who responded to aspirin, the study found.

Read More:

Paramedics should play a larger role in early stroke care

Stroke is a lead killer in South Africa

Depression after stroke linked to troubled sleep

Image: Aspirin tablets from Shutterstock

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