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Trial Stopped: Warfarin Therapy Reaffirmed for Stroke Prevention

For release: Thursday, September 5, 1996

BETHESDA, MD. Warfarin, a standard blood-thinning drug used to prevent stroke, worked so well in certain high-risk patients in a recent clinical trial that the study was halted early. Results of the Stroke Prevention in Atrial Fibrillation III (SPAF III) trial, funded by the National Institute of Neurological Disorders and Stroke (NINDS), are published in the September 7 issue of The Lancet.* The study demonstrated a 75 percent reduction in the risk of stroke for people with a common type of irregular heartbeat called atrial fibrillation.

The trial tested whether a combination of a fixed, low dose of warfarin plus aspirin would work as well as standard warfarin therapy. Investigators stopped the study about one-third of the way to expected completion when the benefit of standard warfarin therapy over the combination therapy was clear. The multicenter clinical trial included 1,044 patients at 20 medical centers in the United States and Canada.

"People with atrial fibrillation are six times more likely to have a stroke than people without atrial fibrillation. Optimal use of standard warfarin therapy in these patients could prevent as many as 40,000 strokes a year in this country and save nearly $600 million a year in health care costs," said Audrey S. Penn, M.D., NINDS Deputy Director. "The costs of these strokes to the health care system cannot begin to describe the devastating impact stroke has on individuals and their families."

SPAF III reaffirms the findings of two previous studies showing that many persons who have atrial fibrillation should be treated with standard warfarin therapy. Warfarin is often underused in everyday medical practice in part because the therapy requires close clinical monitoring and frequent blood tests. The exact dose of warfarin must be individually adjusted for each patient so that there is an adequate amount to prevent stroke yet not so much that unnecessary bleeding results.

"The benefits in stroke prevention shown in this SPAF III trial outweigh the risk of bleeding when warfarin is administered under strict medical supervision," said Michael D. Walker, M.D., Director of the NINDS Division of Stroke and Trauma. "Physicians should be assured that they can offer a stroke prevention therapy that has been upheld in three robust, multicenter investigations."

SPAF III was the latest in a series of trials coordinated by Robert G. Hart, M.D., and David G. Sherman, M.D., from the University of Texas Health Sciences Center at San Antonio. The trials, spanning the last decade, have been designed to find the best way to reduce strokes in the 2 million Americans who have atrial fibrillation. In people with atrial fibrillation, blood clots can form in the upper chambers of the heart. These clots can break loose and be pumped into the blood stream and carried to the brain where they can cause a stroke. Atrial fibrillation primarily affects people over the age of 60 and is diagnosed by having an electrocardiogram. While some people have no symptoms, others experience a sensation of rapid heart beats or skipped beats.

The SPAF trials have involved more than 3,800 patient volunteers with atrial fibrillation. Results from SPAF I, reported in 1990, found an 80 percent reduction in stroke risk for persons with atrial fibrillation who receive treatment with aspirin or warfarin. Both these drugs help prevent the formation of blood clots, but warfarin is a more effective blood thinner than aspirin. The SPAF II study, reported in 1994, identified the 60 percent of people with atrial fibrillation for whom a daily adult aspirin provides adequate protection against stroke with minimal complications. This group consists of those younger than 75 and those older than 75 with no additional stroke risk factors such as high blood pressure or heart disease. SPAF III studied the remaining 40 percent of atrial fibrillation patients with additional risk factors for stroke and for whom warfarin had been shown effective.

The NINDS is the nation's principal supporter of research on the brain and nervous system and is part of the National Institutes of Health, located in Bethesda, MD.

*Stroke Prevention in Atrial Fibrillation Investigators. "Adjusted-dose warfarin versus low-intensity, fixed-dose warfarin plus aspirin for high-risk patients with atrial fibrillation: Stroke Prevention in Atrial Fibrillation III randomized clinical trial." The Lancet, September 7, 1996, 348, 633-638.

Originally prepared by Margo Warren and Norman Oliver, NINDS Office of Communications and Public Liaison.

Last Modified August 7, 2009