Blood thinners can help prevent dangerous clots, but they also come with risks for excess bleeding.
Dr Gregg Fonarow, a professor of cardiology at the University of California, previously said that it's known that aspirin use by patients on anticoagulant therapy doubles the risk of bleeding.
Now, new research shows that use of the medications does boost the odds of "subdural hematomas" – bleeds occurring within the skull and near the brain. And some blood thinners carry higher risk than others.
The study was published in the Journal of the American Medical Association.
The Danish research team stressed that the results don't mean patients who need blood thinners should avoid them altogether – just that their data adds to decisions around their use.
A Health24 article stresses that people taking blood thinners to prevent clots in their legs or lungs may put themselves at risk for serious internal bleeding if they also take common painkillers such as aspirin or ibuprofen.
These over-the-counter painkillers – called non-steroidal anti-inflammatory drugs (NSAIDs) – include Advil, Aleve, Bufferin, Excedrin, Motrin and Nuprin, as well as aspirin. Patients who use blood thinners such as warfarin, Eliquis, Xarelto or Pradaxa should not take them.
The risk-benefit equationco
"The present data adds one more piece of evidence to the complex risk-benefit equation of [blood thinner] use," wrote a team led by Dr David Gaist, of Odense University Hospital and the University of Southern Denmark.
Despite the bleeding risk, the study authors added: "It is known that these drugs result in net benefits overall in patients with clear therapeutic indications."
In the study, Gaist's team tracked data on more than 10 000 Danish patients, aged 20 to 89, who were diagnosed with a first-ever subdural hematoma between 2000 and 2015.
The investigators then compared that group to more than 400 000 people in the general population.
Different blood thinners, different effects
Among the patients with the bleeds, 47% were taking anti-clotting medications. These included low-dose aspirin; another class of drugs known as vitamin K antagonists (which includes Coumadin/warfarin); clopidogrel (Plavix); or other blood-thinning medications.
Low-dose aspirin was associated with a small risk of the subdural hematoma bleed; use of clopidogrel plus a second blood-thinning pill was associated with a moderate risk; and use of a vitamin K antagonist (VKA), such as warfarin, carried a higher risk, the researchers said.
With the exception of low-dose aspirin (either alone or combined with the blood-thinner dipyridamole), concurrent use of more than one anti-clotting drug was related to substantially higher subdural hematoma risk, the study found.
The risk was particularly high among patients taking a combined treatment of a VKA (such as warfarin) plus a second drug such as low-dose aspirin or clopidogrel.
Use drugs under 'stringent control'
Finally, the Danish team found that the use of blood thinners rose in the general population in Denmark from 2000 to 2015 – as did the rate of subdural hematomas. The findings showed that the largest increase in subdural hematoma rates occurred in patients older than 75.
As director of the neurointensive care unit at Winthrop-University Hospital in Mineola, New York, Dr Rajanandini Muralidharan often works with patients who need blood thinners.
Reviewing the new study, she agreed that the use of drugs such as Coumadin/warfarin "should be carefully considered in the elderly" and, if they are used, this should be done only under stringent controls.
Newer (but more expensive) blood thinners – drugs such as Pradaxa, Xarelto, and Eliquis – "are an alternative option, given their lower risk of intracranial bleeding", Muralidharan said. However, in rare cases these medicines can also cause dangerous bleeding episodes, she noted, and as yet there are few approved drugs out there to help reverse these events.