Warfarin Proven Effective

A Harvard physician writing in today's New England Journal of Medicine urges doctors to carefully monitor patients using a drug proven safe and effective at preventing strokes.

In a double-binded study published in today's Journal, Yale Medical School cardiologist Dr. Michael D. Ezekowitz confirms a number of previous studies demonstrating that low doses of warfarin, an anticlotting drug, prevent strokes in patients with a condition known as atrial fibrillation.

But Associate Professor of Medicine and Health Care Policy Dr. Daniel E. Singer, who was involved in a previous Boston-area study of warfarin, cautions in an editorial published in the same issue that some complications are possible if patients are not monitored carefully.

Atrial fibrillation, which affects up to ten percent of people over 80, results from uncoordinated contraction of the two upper chambers of the heart. Irregular blood flow results, causing blood to pool in the chambers and clot. Strokes can then occur if the clots travel around the blood vessels and block blood flow.

Doctors estimate that of 500,000 strokes sustained by U.S. residents every year, 15 percent, or 75,000, are linked to atrial fibrillation. Warfarin has the capability to prevent up to 80 percent of these 75,000 strokes, Singer said.

Warfarin, known in North America by its trade name Coumadin, works by blocking Vitamin K-de-pendent factors involved in clotting activation. But because warfarin slows clotting, the drug can be dangerous to patients prone to ulcers or head injuries, which can cause life-threatening internal bleeding.

"If warfarin is used more widely in less controlled conditions, it may cause more trouble than observed in clinical trials," Singer said in an interview yesterday. "On balance, the message that comes out of these remarkable trials is that every patient with chronic atrial fibrillation should give warfarin a good look."

Singer said that while some researchers have proposed that patients be prescribed aspirin to prevent clotting, findings about its properties have so far been too conflicting to ensure its effectiveness.

"The effects of aspirin are hardly comparable to warfarin for this condition," he said. "I'm skeptical that there's much benefit."