Portland, OR—More than one-fifth of patients prescribed a direct-acting oral anticoagulant (DOAC) for atrial fibrillation were receiving an inappropriate dose of the blood-thinners, with under-dosing being most common, according to a new study.

The report in the Journal of the American Heart Association notes that dosing guidelines for atrial fibrillation recommend alteration based on age, renal function, body weight, and drug-drug interactions. Yet Oregon Health & Science University–led researchers point out the lack of data describing the frequency and factors associated with prescription of potentially inappropriate doses.

In the ongoing SAGE-AF (Systematic Assessment of Geriatric Elements in Atrial Fibrillation) study, the study team performed geriatric assessments, looking at frailty, cognitive impairment, sensory impairments, social isolation, and depression for participants with atrial fibrillation. Patients, who were aged 65 years or older, had CHA2DS2VASc ≥2 and no anticoagulant contraindications.

Researchers developed an algorithm to analyze DOAC dose appropriateness, taking into account drug-drug interactions, age, renal function, and body weight. They also evaluated whether geriatric impairments were related to inappropriate dosing.

Of 1,064 patients prescribed anticoagulants, 460 received a DOAC. Participants were aged 74±7 years, 49% were women, and 82% were white.

The study determined that 23% of participants received an inappropriate DOAC dose. Most of those, 78%, were underdosed, while 22% were overdosed.

Results indicate that, among participants receiving an inappropriate dose, 12 (11%) were identified using the drug-drug interactions criteria and would have otherwise been misclassified.

In multivariable regression analyses, inappropriate DOAC dosing was found to be associated with:
• Older age
• Higher CHA2DS2VASc score
• History of renal failure

On the other hand, geriatric conditions were not associated with inappropriate dosing.

“In this cohort, over 20% of older patients with atrial fibrillation treated with DOACs were prescribed an inappropriate dose, with most being underdosed,” the authors conclude.

“Drug-drug interactions were common. Factors that influence prescription of guideline-nonadherent doses may be perception of higher bleeding risk or presence of renal failure in addition to lack of familiarity with dosing guidelines.”

The authors recommend that clinicians systematically assess for drug-drug interactions, in addition to age, body weight, and renal function, for prescription of accurate DOAC dose.

DOACs, including dabigatran, apixaban, rivaroxaban, and edoxaban, have been approved by the FDA for the prevention of thromboembolic events in patients with nonvalvular atrial fibrillation.

 « Click here to return to Weekly News Update.