A heart-rending study: Warfarin may be underused by those who need it most.

According to a new study published in the journal Stroke, more than two-fifths of elderly patients with atrial fibrillation (a type of abnormal heart rhythm) are not using the blood-thinner warfarin, an anticoagulant commonly known by the trade name Coumadin. This drug is prescribed to prevent strokes associated with clots in the atria, the upper heart chambers. These can become emboli, or clots that travel to the brain. This failure to take warfarin may be responsible for an excess of strokes, as well as financial burdens to the economy.

Researchers analyzed claims data from 120,000 Medicare beneficiaries with a form of atrial fibrillation (AF) known as NVAF (non-valvular AF) and found that compared to the 41.5 percent of patients not taking warfarin, those who were medicated experienced a 27 percent lower risk of stroke within two years. Meanwhile, they calculated that the direct costs of treating strokes resulting from atrial fibrillation was more than $2.5 billion annually.

Warfarin can, however, have undesirable side effects, including bleeding complications when taken in excess, and the dose needs to be monitored with blood tests at least once or twice a month. But, as Stanford University cardiology fellow Dr. James V. Freeman tells Reuters, physicians “may overestimate this risk and underestimate the relative benefit [of taking warfarin] in terms of preventing stroke and other clot-related complications.”

ACSH's Dr. Gilbert Ross agrees, noting that, “warfarin can be a dangerous drug...that’s why it is sometimes easier for doctors to forgo prescribing it. This study does not indicate how many patients were not taking warfarin because of contraindications, such as a history of serious bleeding problems or certain drugs that can interact adversely. But the decision to take medication for stroke prevention has to be individualized for each patient. Thankfully, new drugs that require less monitoring are in the pipeline and will presumably replace warfarin.”