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Release: Nov. 14, 2001


Warfarin, aspirin provide similar benefits in stroke prevention

IOWA CITY, Iowa -- Research results from a $35 million, eight-year study involving more than 2,000 patients show that aspirin and warfarin are essentially comparable in their ability to prevent recurrent strokes in patients who have had a prior ischemic stroke and did not have atrial fibrillation. The results are published in the Nov. 15 issue of the New England Journal of Medicine.

After a decade of earlier research that verified the drug's benefit, physicians now routinely prescribe the blood thinner warfarin to prevent first and recurrent strokes in individuals who have atrial fibrillation, a condition characterized by an irregular and rapid rhythm in the atrial chambers of the heart. People with atrial fibrillation are at risk for stroke because pooled blood in their hearts can lead to clots which, dislodged and carried to the brain (a process known as embolism), can occlude brain arteries, blocking blood flow, resulting in brain damage known as an ischemic stroke. Because warfarin use has a reputation for complications in the form of hemorrhage, many physicians have been hesitant for its use even in atrial fibrillation.

Until now there has been no research about warfarin's value compared to aspirin in the prevention of stroke in the majority of people who do not have atrial fibrillation yet have had a prior ischemic stroke. A University of Iowa Health Care team, including Harold Adams, M.D., and Patricia Davis, M.D., participated a in the multi-center trial, which was coordinated by physicians at Columbia University.

"We already knew that treating patients with either aspirin or warfarin helped prevent another stroke," Adams said. "Now, we also know that it is safe to use aspirin or warfarin therapy, whether the patient has atrial fibrillation or not."

The study included 2,206 individuals who had suffered from an ischemic stroke due either to local blockage in the brain vessels from hardening of the arteries or from a clot arising from a source outside the brain carried through arteries to the brain vessels. The study did not include patients whose stroke was associated with atrial fibrillation (approximately 15 percent of all cases of stroke) or from any form of hemorrhage (approximately 20 percent of all cases).

In the study, half the patients received warfarin and the other half took aspirin, each patient receiving pills that appeared to be warfarin or aspirin, in a fashion known as double-blind, in which neither the patients nor the investigators were aware of who received which medication. Since individuals who take warfarin need to have their blood monitored for its ability to clot, the investigators were sent true laboratory values for those patients actually on warfarin but for those on aspirin, they were sent false values, values which suggested the patients were actually on warfarin therapy.

After analyzing the data, the researchers found that the group of patients taking aspirin had no statistically significant differences in the risk in having a subsequent stroke as the group taking warfarin. There was also no statistically significant difference in the risk of major bleeding in either of the two groups.

Aspirin, with its low cost, wide availability, ease of use and lack of need for the monitoring needed for warfarin, may remain the most widely used of the two drugs, Adams says. Its use in combination with other drugs having similar action seems promising. However, he also stressed that earlier concerns that warfarin was a more hazardous therapy proved unfounded at the doses used in the study. Those physicians having other indications for warfarin therapy should take comfort in its comparative safety and efficacy even when there is no atrial fibrillation present, and have no reason to switch to aspirin should a stroke occur.

"This study shows that it is ultimately up to the patient and physician to decide which therapy is the best course of action," Adams said.

Although both drugs will provide a reduction in the risk of having another stroke, the research showed that at least 8 percent per year of the patients taking either warfarin or aspirin still experience another stroke. Adams says further research is ongoing to develop new methods to reduce this continuing recurrence rate.

Stroke is the third largest cause of death in the United States, ranking behind "diseases of the heart" and all forms of cancer, according to the American Heart Association. Stroke is a leading cause of serious, long-term disability in the United States, the heart association says. Approximately 500,000 people suffer a new stroke each year; an additional 100,000 cases are recurrent attacks.

The symptoms of a stroke include a sudden numbness or weakness of the face, arms or legs, especially on one side of the body, a sudden loss of vision in one or both eyes, a severe headache, sudden confusion, trouble speaking or understanding, and sudden trouble walking, dizziness or loss of balance and coordination. Such symptoms are signs of a potential "brain attack" and require immediate medical evaluation. Neurologists say when treatment for stroke begins soon after the onset of symptoms there is a much greater likelihood for recovery.

The National Institute of Neurological Disorders and Stroke funded the trial. Bayer Corp. provided aspirin and placebo aspirin at no cost for the study. DuPont Pharmaceuticals Co. donated the warfarin and placebo-warfarin and provided $600,000 for the formulation of both the medications used in the trial. The findings of the study affect approximately 70 percent of all stroke patients; only 15 percent of patients with ischemic stroke also have atrial fibrillation.

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