Atrial fibrillation, often called AFib, is the most common type of irregular heartbeat. Instead of beating in a steady rhythm, the upper chambers of the heart beat quickly and unevenly.
This can allow blood to collect inside the heart, where clots may form.
If a clot travels to the brain, it can block blood flow and cause a stroke. Because of this, many people with AFib need long-term treatment to lower their stroke risk and keep their heart rate under control.
Doctors often prescribe blood-thinning medicines, also known as anticoagulants, to reduce the chance of blood clots. Two commonly used drugs are apixaban and rivaroxaban. Many patients also take medicines that slow the heart rate, including diltiazem or metoprolol.
These medicines are widely used and are generally effective, but combining several drugs can sometimes increase the risk of side effects.
Researchers have long known that people do not all respond to medicines in the same way. Age, kidney function, liver function, other health conditions, genetics, and the use of additional medications can all affect how the body breaks down drugs.
Some medicines can also interfere with each other, causing drug levels in the blood to become too high or too low. This is especially important for older adults, who often take several medicines every day.
A new study published in the medical journal JAMA has raised concerns about one common drug combination used to treat atrial fibrillation.
The research suggests that people taking the blood thinners apixaban or rivaroxaban together with diltiazem may have a higher risk of serious bleeding than those taking the same blood thinners with metoprolol.
The study was led by Dr. Eli Zimmerman of Northwestern University and included Medicare patients aged 65 years and older.
The researchers examined medical records from people who began treatment with apixaban or rivaroxaban together with either diltiazem or metoprolol between 2012 and 2020. They then compared the health outcomes of the two groups.
The results showed that people taking diltiazem were about 20% more likely to be hospitalized for serious bleeding or die from bleeding-related problems than people taking metoprolol. However, the researchers did not find major differences between the two groups in the rates of stroke, blood clots, or several other cardiovascular outcomes.
The researchers believe the higher bleeding risk may be linked to the way diltiazem affects the body’s ability to process certain blood thinners.
When the drugs are taken together, blood thinner levels may become higher in some patients, increasing the chance of dangerous bleeding. More research is needed to fully understand why this happens and why some people appear to be more affected than others.
Dr. Zimmerman said that understanding how individual patients respond to medications is an important step toward safer and more personalized care. His team hopes future studies will determine whether monitoring drug levels more closely could help doctors identify patients at higher risk and reduce bleeding complications.
The findings do not mean that patients should stop taking diltiazem or any blood thinner on their own. These medicines are highly effective and may be the best treatment for many people.
Instead, the study highlights the importance of discussing all medications with a healthcare provider, especially when starting a new prescription. Doctors can weigh the benefits and risks for each individual patient and decide which treatment is most appropriate.
In addition to taking medicines as prescribed, maintaining a healthy lifestyle can also support heart health. Controlling blood pressure, eating a balanced diet, staying physically active, avoiding smoking, limiting alcohol, and attending regular medical check-ups all play important roles in reducing the risk of heart disease and stroke.
The research was published in JAMA.
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