Improper Anticoagulant Therapy Increases Bleeding Risk

A new study reveals that many patients receiving warfarin for the management of atrial fibrillation (AF) or venous thromboembolism (VTE) also take aspirin without a clear therapeutic indication.

Researchers at the University of Michigan (U-M; Ann Arbor, USA), Huron Valley Sinai Hospital (Commerce Township, MI, USA), and other institutions conducted a registry-based cohort study involving 6,539 adults (50.9% men) at six anticoagulation clinics in the state of Michigan receiving warfarin therapy for AF or VTE (without documentation of a recent myocardial infarction or history of valve replacement), in order to evaluate the frequency and outcomes of combination anticoagulation therapy without clear indication.

Of the study cohort, 2,453 patients (37.5%) who had no clear therapeutic indication for aspirin were receiving a combination warfarin and aspirin therapy. Of these, 5.7% experienced major bleeding events after one year, compared to 3.3% of those on warfarin only. The combination therapy group was also hospitalized for bleeding significantly more often. However, there was no difference in stroke or heart attack outcomes at one year, and mortality rates were similar between both groups, at 2.3%. The study was published on March 4, 2019, in JAMA Internal Medicine.

“Nearly 2,500 patients who were prescribed warfarin were taking aspirin without any clear reason, over a seven-year period. No doctors really own the prescribing of aspirin, so it's possible it got overlooked,” said senior author vascular cardiologist Geoffrey Barnes, MD, MSc, of the U-M Medical School. “The combination does make sense for a small number of people; patients who may need to be on both medications include those who have had a recent heart attack, recent coronary stent placement, or bypass surgery, prior mechanical valve surgery, or known peripheral artery disease.”

“Clinicians should ask their patients who are anticoagulated with warfarin if they're taking aspirin as well. For the patients who are on both therapies, clinicians should review their medical history to determine if it's really necessary to be on both drugs,” said lead author hematologist Jordan Schaefer, MD, of M-U Medicine. “There's been some hint of this being an issue for a long time. Now, based on these new findings, we're working to reduce the number of patients on aspirin without a clear reason for both drugs.”

Aspirin (acetylsalicylic acid) is a salicylate drug often used as an analgesic to relieve minor aches and pains, as an antipyretic to reduce fever, and as an anti-inflammatory medication. Aspirin's efficacy as an anticlotting agent and its widespread use as a preventive treatment for heart attacks and strokes have turned it into one of the most widely used medications in the world, with an estimated 40,000 tons of it being consumed each year.

Related Links:
University of Michigan
Huron Valley Sinai Hospital