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Studies Highlight Problems With Anti-Clotting Drug

Warfarin is tough to prescribe and use, doctors say

THURSDAY, March 9, 2006 (HealthDay News) -- Two new studies show why doctors wish they had a blood clot-preventing drug that could work better than warfarin, the current standard.

Warfarin is taken by many people for a number of reasons -- to prevent clots from forming on an artificial heart valve, for example. Most notably it is prescribed for people with atrial fibrillation, an abnormal heartbeat common among older individuals that increases the risk that a clot will form in the heart and travel to the brain, causing a stroke.

But one study that followed the treatment of 405 people aged 65 and older with atrial fibrillation found that only 51 percent of them were on warfarin when they left the hospital. Several reasons were given by doctors for not prescribing the drug, said a report by physicians at Boston University that appears in the April issue of Stroke.

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

Warfarin is a difficult drug to handle, for both the doctors who prescribe it and the people who take it. Frequent blood tests are needed to determine that the given dose causes just the right amount of clot-preventing activity, rather than bleeding episodes that can be dangerous.

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

The second study in the journal looked at the real-life experiences with warfarin of more than 17,000 Medicare beneficiaries with atrial fibrillation who were hospitalized in 1998 and 1999.

"It was pretty disappointing," said research leader Dr. Brian F. Gage, an associate professor of medicine at Washington University in St. Louis. "It [warfarin] was only half as effective in these Medicare beneficiaries than 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 percent of cases, the study found.

One major reason for the underuse of warfarin and its less-than-effective results when prescribed was the need for the constant monitoring -- a blood test every few weeks, Gage said. "Monitoring for many patients was infrequent," he said. "Tests were done every three months or sometimes at longer intervals."

Warfarin use and monitoring was especially low for blacks and Hispanics, the study found. Doctors prescribed or planned to prescribe warfarin for 49.7 percent of whites at hospital discharge, but only 43.2 percent of blacks and 40.2 percent of Hispanics. After discharge, 17.9 percent of blacks and 13.6 percent of Hispanics were monitored less frequently than every 90 days, compared to 7.9 percent for whites.

Some policy changes could improve benefits from the drug, Gage said. For instance, most people get their blood-test results by phone, but Medicare doesn't reimburse for those tests unless the assessment is made in a doctor's office, he said.

"It's a hassle for patients, physicians and staff," Gage said. "This kind of reimbursement is a disincentive for monitoring."

But, he added, "in the long term what we need are easier drugs to handle." One drug that looked promising in early testing fell by the wayside when it was found to cause liver problems in a small percentage of those taking it.

"In a couple of years, we should have alternatives to warfarin," Gage said. Then, after a pause, he added, "Make that two to five years."

More information

The National Library of Medicine provides more about warfarin.

SOURCES: Brian F. Gage, M.D., associate professor, medicine, Washington University, St. Louis; April 2006 Stroke
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