Many Patients Using Anticoagulants Are Taking Aspirin Daily Too

A study found that 37% of patients who took warfarin also took aspirin. That could place patients at a significantly higher risk of adverse outcomes, including major bleeding events.

Physicians who've prescribed anticoagulants to their patients should double-check to make sure they're not using aspirin too, a new study out of Michigan Medicine suggests.

The study, published this month in JAMA Internal Medicine, found that 37.5% of the 6,539 patients reviewed were receiving the anticoagulant warfarin and aspirin without a clear indication, and that these patients were at a significant increase in adverse outcomes.   

"Nearly 2,500 patients who were prescribed warfarin were taking aspirin without any clear reason, over a seven-year period," said senior author Geoffrey Barnes, MD, a vascular cardiologist and an assistant professor of internal medicine at U-M Medical School. "No doctors really own the prescribing of aspirin, so it's possible it got overlooked."

The study cohort included 6,539 patients who were enrolled at six anticoagulation clinics in Michigan between 2010 and 2017.

In this study, 5.7% of those using aspirin and warfarin experienced major bleeding events after one year, compared to 3.3% of those on warfarin only. The combination group that was using aspirin without a clear indication also visited the emergency department and/or were hospitalized for bleeding significantly more often.

There wasn't a difference in stroke or heart attack outcomes that are typical uses for aspirin, Barnes says. The mortality rates at one year were similar between both groups, and 2.3% of those on both medications had a thrombotic event at one year compared to 2.7% of those on warfarin alone.

Barnes spoke with HealthLeaders about the findings. The following is an edited transcript.

HLM: More than one-third of patients were taking both aspirin and warfarin. Why is that percentage so high?

Barnes: You're seeing here is a two factors. First is, unlike many randomized trials, we included all patients who were managed in our anticoagulation clinics. So we were not filtering out only the healthy patients are only those who did not have risk of bleeding. You get a broader perspective of what kind of risk patients are at when you follow them over the long term. This was a practice-based, real-world cohort as opposed to a randomized trial cohort.

Secondly, we've known from various is other studies that the more blood thinners you take, the higher your risk of bleeding. When these patients are taking both aspirin and warfarin together, that's going to increase their overall risk of bleeding.

HLM: If they didn't consult with a physician, what made these patients think it was a good idea to take both medications?   

Barnes: We don't know exactly why they were taking aspirin. However, there are a couple potential scenarios. The first is that this is somebody who maybe was on aspirin for primary prevention and then developed Afib or DVT and so was started on warfarin, but nobody thought to stop aspirin.

Another scenario is they were on warfarin for Afib and they read or heard something that said, 'you should take aspirin to help prevent a heart attack.' That's out there in the in the media quite a bit. And so they said, 'Oh, well, it's just over the counter. It's got to be safe.' So they go ahead and take it.

The third is that maybe they had a good reason to be on aspirin. Maybe they had a coronary stent that was placed or something, and so they were on aspirin. As time went on, that coronary stent was no longer recent, no longer fresh, and so the indication for aspirin is not quite as strong and yet nobody bothered to think about stopping aspirin.

HLM: Is this something that should be addressed on the patient level, or is this a health systemwide issue that requires new protocols?

Barnes: It's actually both. The first thing we know is that aspirin is a really difficult drug to study and understand because it's not prescribed. Many clinicians do not know whether their patients are taking aspirin or not, because they're not routinely examining their medical record.

Secondly, we as healthcare providers don't always do a great job reconciling the medication list. Even though patients are coming into clinic are coming in for procedures, we don't do a great job making sure we know which drugs they are taking, or they're not taking. Right off the bat, there are some challenges to even knowing when the situation exists.

Systematically there are opportunities for us to build in a screen so you could run a report of all your patients who are on multiple antibiotics, and then cross reference that with sort of those who have indications like heart valve replacement, or recent stent placement or something, and those who don't.

In our situation, we have these big robust anticoagulation clinics. We've put in place a process where we will screen anyone who's on aspirin at the time to start warfarin and say 'is it really necessary?'

Of course, it always comes down to the individual patient level. You have to make a personalized decision. Some are going to be clear cut. Others may be more questionable.

What do you do if somebody had a coronary stent a year or two ago? Should they be an aspirin or not? These are questions that we have to ask other specialists then make the best decision for each individual patient.