People with atrial fibrillation (Afib) who took low doses of blood-thinning drugs known as direct oral anticoagulants (DOACs) experienced more bleeding during the first three months of treatment. About 1 in 5 patients on low doses of DOACs had high levels of the medications in their blood compared to people taking standard doses of the medications, according to a study published Thursday in Blood Advances.
Some studies have shown that patients with Afib who take DOACs have fewer strokes and blood clots than those with Afib who take warfarin, an older blood-thinning medication.
Unlike with warfarin, most people taking DOACs don’t undergo regular tests to measure blood levels of the medication. However, recent studies indicate that blood levels of DOACs can vary between patients and that levels that are too low or too high may boost their risk for blood clots and bleeding episodes. Many people taking the drugs need them for the rest of their lives.
“We found that 58% of bleeding complications occurred in patients who were treated with low doses of DOACs,” Gualtiero Palareti, MD, of the Arianna Anticoagulation Foundation in Bologna, Italy, and the study’s coordinator, said in a statement. “Not only did the use of low doses not reduce bleeding risk, it also did not prevent patients from developing high blood levels of the medication.”
Palareti’s team published another study in April in Blood Advances, which reported that people with the lowest blood levels of their DOAC medication had the most blood clots during a one-year follow-up period. The current study looked at the relationship between measured blood levels of DOACs and bleeding events.
Investigators examined data on 1,657 people with Afib. The team evaluated bloodwork drawn within two to four weeks of beginning treatment with a DOAC and immediately before they were to take their next pill, when blood levels of the drug were expected to be at their lowest. The people were evaluated during the first month of treatment and had follow-up visits every three to four months for a year. Then researchers looked at bleeding events, blood clots, heart attacks, strokes and deaths during that same year.
Among participants, 3.1% had bleeding events, and 58% of them occurred in patients treated with low doses of a DOAC. About 30% of all bleeding events happened in people with the highest levels in their blood. Bleeding events occurred significantly more frequently in patients who had the highest blood levels of their medication during the first three months of starting treatment.
“Our findings indicate that treatment with low doses of a DOAC does not necessarily prevent the occurrence of high blood levels of the drug,” Palareti said. “This predisposes patients to a higher risk of bleeding during the first three months of treatment — a period when the risk of bleeding due to oral anticoagulants is already elevated.”
After the first three months, the risk of bleeding events wasn’t linked to low-dose treatment or blood levels of the medication.
The takeaway: Measure medication blood levels after they start and tailor the dose based on that to avoid low or high blood levels and reduce bleeding and clotting complications, especially in people on low doses, the authors noted.
