Two recent studies examined the difficulties of using the drug warfarin, a clot- preventing drug that is often prescribed for people who have atrial fibrillation, an abnormal heartbeat. Common among older individuals, atrial fibrillation increases the risk that a clot will form in the heart and travel to the brain, causing a stroke.

Warfarin is a difficult drug to manage-for both the doctors who prescribe it and the people who take it. Frequent blood tests are necessary to make sure that the dosage prescribed creates just the right amount of clot-preventing activity. Too much warfarin can cause dangerous bleeding episodes.

The First Study: Why It's Not Prescribed

One study at Boston University followed the treatment of 405 people, age 65 and older, who had atrial fibrillation. According to the researchers, only 51% of the patients were taking warfarin when they left the hospital. Doctors gave several reasons for not prescribing the drug.

In one-third of the cases, doctors cited current or chronic bleeding episodes as the reason for not prescribing warfarin. In another one-third, the physicians cited falls by patients that had caused a head injury or a broken bone. And the reason given in 14% of the cases was the patient's refusal to take the drug or a history of not taking prescribed drugs.

"We need to better understand the underlying mechanism of clotting to find novel drugs that lessen the risk of hemorrhage," says study author Dr. Elaine M. Hylek, an associate professor of medicine at Boston University.

The Second Study: Real-Life Experiences

The second study looked at the real-life experiences of more than 12000 Medicare beneficiaries who were taking warfarin for atrial fibrillation.

"It was pretty disappointing," says lead researcher, Dr. Brian F. Gage, an associate professor of medicine at Washington University in St. Louis. "Warfarin was only half as effective in these Medicare beneficiaries as in clinical trials."

Even when warfarin use was clearly indicated-in people who had no reason for not taking the drug and had other risk factors for stroke-it was used in only 65% of the cases, the study found.

One major reason for the underuse of warfarin was the need for constant monitoring through a blood test every few weeks, Gage says. "Monitoring for many patients was infrequent," he says. "Tests were done every three months or sometimes at longer intervals."

Gage thinks the infrequent monitoring could be due to some Medicare policies. For example, most people get their blood test results by phone, but Medicare doesn't reimburse patients unless the assessment is made in a doctor's office, he says. "It's a hassle for patients, physicians and staff," Gage explains. "This kind of reimbursement is a disincentive for monitoring."

But, "In the long term, what we need are easier drugs to handle. In a few years, we should have alternatives to warfarin," Gage predicts.

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