One in three seniors prescribed the blood thinners dabigatran and rivaroxaban are not taking the medications as recommended, increasing their risk of stroke, transient ischemic attack (mini stoke) or death by 80 per cent, according to a new study from the Institute for Clinical Evaluative Sciences (ICES).

Dabigatran and rivaroxaban are novel oral anticoagulants (NOACs) approved for stroke prevention in patients with atrial fibrillation (an irregular heart rhythm). The drugs are meant to be used continuously to ensure efficacy, as their effects wear off otherwise.

In the study, published recently in Heart, the researchers looked at 25,976 Ontario patients with atrial fibrillation from January 1998 to March 2014 who were prescribed dabigatran or rivaroxaban.

“One in three patients is not taking their medication as prescribed within six months of starting either dabigatran or rivaroxaban, and our study shows that this is associated with an 80 per cent increased risk of stroke, mini stroke or death in this population,” says Dr. Cynthia Jackevicius, author of the study and senior adjunct scientist with ICES.

The study found that at six months, 36.4 per cent of patients were no longer taking their prescription for dabigatran, while 31.9 per cent of patients were no longer taking their prescription for rivaroxaban. The researchers defined non-adherence as a gap in dabigatran or rivaroxaban prescriptions equal to or greater than 14 days.

The researchers found that patients who were nonpersistent to dabigatran and rivaroxaban were four times and more than six times respectively, more likely to have a stroke or mini stroke than those who continued to take their medication as prescribed.

“Patients need to know the risks associated with not taking their medications as prescribed and clinicians need to be aware that many patients prescribed these drugs aren’t taking them as intended,” adds Jackevicius.

NOACs are more convenient than older anticoagulants like warfarin because they don’t have as many food and drug interactions and don’t require monthly blood tests. But the study’s authors suspect the lack of required monitoring by doctors and pharmacists may inadvertently be one of the causes of non-adherence to the drugs.

“There appears to be an assumption that patients would be more adherent to novel oral anticoagulants than the older drugs because they are more convenient but we didn’t find that in this study.  In fact, a previous study in Ontario found that nearly 32 per cent of patients using warfarin discontinued therapy within one year, a rate similar to that found in our current study for dabigatran and rivaroxaban,” says Jackevicius.

The researchers add that it’s important to reinforce the importance of taking these drugs as prescribed to both patients and clinicians.