THURSDAY, Aug. 28 (HealthDay News) — Only 40 percent of patients with atrial fibrillation, a known risk factor for stroke, who did suffer a stroke were taking the anti-clotting drug warfarin, a new study found.

Among those taking warfarin, 75 percent weren’t getting the dose needed to prevent a stroke. And an additional 25 percent were taking medications that were less effective at preventing clots or no medication at all, according to the report by Canadian researchers.

“These are missed opportunities for stroke prevention,” lead researcher Dr. David J. Gladstone, a stroke neurologist at the University of Toronto, said in a prepared statement. “Sadly, we frequently see patients admitted to a hospital with a devastating stroke who are known to have atrial fibrillation, yet were either not taking warfarin or were taking a dose that is not therapeutic. We consider these to be potentially preventable strokes.”

The findings are published online Aug. 29 in the journal Stroke.

Gladstone’s team collected data on 2,135 stroke patients listed in the Registry of the Canadian Stroke Network. Among these patients, 597 were diagnosed with atrial fibrillation, an irregular heartbeat, before their stroke. For these patients, 60 percent of the strokes were disabling, and 20 percent were fatal.

Warfarin, by thinning the blood, helps prevent clots from developing and reduces the risk of stroke by about 67 percent in people with atrial fibrillation (AF). Strokes caused by AF can be more severe than other strokes, and studies have shown that warfarin can reduce the severity of strokes in patients with atrial fibrillation, the researchers said.

It’s not clear why the rates of warfarin use were so low, the researchers said. “On one hand, we have an extremely effective and cheap medication for stroke prevention — warfarin — yet, on the other hand, it remains under-used in people who would benefit most from it,” Gladstone said.

The study authors believe that efforts are needed to educate physicians and patients about the benefits of warfarin therapy for those with atrial fibrillation. “This is a public health priority, because atrial fibrillation is one of the most common causes of stroke,” Gladstone said. “Many more strokes could be prevented if anti-coagulation therapy were optimized in the population at large.”

Dr. Byron Lee, an assistant professor of cardiology at the University of California, San Francisco, thinks part of the problem may owe to the fact that many patients have problems taking warfarin, because it requires blood tests to monitor its effectiveness. Too low a dose is ineffective, while too high a dose can cause internal bleeding. So, patients need to have their warfarin levels measured at least once a month, he said.

“Patients hate taking warfarin, and doctors hate prescribing it,” Lee said. “This is mainly because it’s a hassle. However, this study confirms that many strokes can be avoided if patients are adequately anti-coagulated. Therefore, both patients and doctors need to do a better job of overcoming the inconvenience of warfarin.”

Dr. John Worthington is a stroke physician at Liverpool and Northern Beaches Hospitals at the University of New South Wales in Sydney, Australia, who wrote an accompanying editorial in the journal. He said it’s essential for patients with atrial fibrillation to receive warfarin to prevent a stroke.

“Warfarin is usually the best and safest available treatment to prevent stroke in people with atrial fibrillation. Increasing the uptake of warfarin would reduce the risk of death and disability of stroke,” he said.

Worthington said patients with AF should ask their doctor why they aren’t being prescribed warfarin