Warfarin may be underused to prevent strokes

NEW YORK (Reuters Health) - The blood thinner warfarin prevents strokes and saves money, but the drug is only used by a little more than half the elderly patients with abnormal heart rhythms who might benefit from it, a new study has found.

An estimated 2.3 million Americans have atrial fibrillation -- electrical disturbances in the heart that cause the organ to beat erratically. The abnormal beating can lead to blood clots that block vessels in the brain, causing so-called ischemic strokes. A form of the condition, called non-valvular atrial fibrillation, or NVAF, is particularly dangerous. NVAF accounts for between 15 and 20 percent of strokes in the United States each year.

Warfarin (sold as Coumadin, Jantoven, Marfarin and others) prevents ischemic strokes by keeping clots from forming. The anticoagulant drug is temperamental, though: too much can cause life-threatening bleeding and even strokes resulting from leaking blood vessels, known as hemorrhagic strokes.

“Physicians are very concerned in the elderly population about significant bleeding events and may overestimate this risk and underestimate the relative benefit in terms of preventing ischemic stroke and other clot-related complications,” said Dr. James V. Freeman, a cardiology fellow at Stanford University who was not involved in the study.

Taken together, the direct costs of treating strokes from atrial fibrillation exceed $2.5 billion a year, the authors write in the journal Stroke. They calculated the health care system would save roughly $1.1 billion of that amount if all patients with atrial fibrillation who are candidates for warfarin received well-controlled treatment with the drug.

The researchers analyzed claims data from more than two million Medicare beneficiaries, of whom about 120,000 had NVAF. Using an indirect measurement of warfarin prescriptions, they determined that 58.5 percent of patients with NVAF were taking the drug, while 41.5 percent were not.

The study authors could not determine from the Medicare data set how many patients not on warfarin were taking aspirin or some other anti-clotting therapy.

Of the 70,057 patients in the database taking warfarin, 5,640 (8 percent) suffered ischemic strokes over approximately two years, compared with 4,130 strokes among 49,707 not taking the drug (8.33 percent).

That translates to a rate of 3.56 strokes per hundred patients per year for those taking warfarin versus 4.63 strokes per hundred patients per year among those not on the drug - or a 27 percent lower stroke rate for the patients on warfarin.

Only a slight increase in incidents of major bleeding among patients taking warfarin was seen, and no increase in hemorrhagic strokes - an unexpected finding that might be explained by patients at high risk for bleeding having been channeled away from warfarin use, the authors note.

Total medical costs also were lower among warfarin patients compared with those not taking the drug, by more than $9,800 a year. Warfarin users had more doctor visits but fewer hospitalizations, the study found.

“When warfarin is prescribed correctly, it is cost-effective, and if it was used more in the (atrial fibrillation) population and used appropriately, then we’d see even bigger reductions in cost,” said lead author Catherine J. Mercaldi, an epidemiologist at United BioSource Corp., a research consulting firm in Bethesda, Md.

The drug does come with unusually burdensome requirements for monitoring and restrictions to avoid interactions. Patients taking warfarin, for instance, are subject to laboratory testing and dose adjustment every couple of weeks and sometimes even more frequently to make sure they are getting enough blood-thinning from the drug but not too much, to avoid excessive bleeding.

“This can be time consuming and labor intensive for both patients and physicians and may be a disincentive for using the drug,” said Freeman.

Patients are also likely to bruise easily and are at heightened risk of excessive bleeding from even minor injuries or during simple procedures such as dental work. In addition, the drug interacts with a significant number of other medications, foods and supplements, requiring patients taking it to watch their diets and keep their doctors informed of any other prescriptions.

The authors note some limitations to their study, including the absence of information about other medications the patients may have been taking.

The study was funded by Boehringer Ingelheim Pharmaceuticals Inc, which received FDA approval in October for its blood thinner Pradaxa, a potential alternative to warfarin for preventing strokes linked to nonvalvular atrial fibrillation. Unlike warfarin, Pradaxa does not require blood testing and can be taken on a twice-daily regimen.

SOURCE: Stroke, online December 9, 2010.