December 16, 2023Journal of Thrombosis and ThrombolysisOpen Access

Adherence to direct or vitamin K antagonist oral anticoagulants in patients with atrial fibrillation: a long-term observational study

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Why the study?

The study was conducted to measure long-term adherence to oral anticoagulants in patients with atrial fibrillation and to identify patient factors associated with adherence.

Structured PICO

Population

30,264 adult patients (≥18 years) with incident non-valvular atrial fibrillation prescribed oral anticoagulants, mean age 72.17, 44.6% female, based in British Columbia, Canada.

Intervention

Oral anticoagulants (DOACs: apixaban, dabigatran, edoxaban, rivaroxaban; or VKA: warfarin)

Outcome

Long-term adherence measured by proportion of days covered (PDC) for each 90-day window from OAC initiation until the end of follow-up

Over half of patients with atrial fibrillation are non-adherent to long-term oral anticoagulant therapy, highlighting the need for targeted adherence-supporting interventions, particularly for older patients and those on VKAs with polypharmacy.

Limitations

Use of administrative data assumes that filling a prescription equates to consuming the medication
Absence of variables known to affect adherence such as education level, frailty, nonprescription drug use, and adverse effects
Frequent switching between OACs hampered robust comparisons between individual agents
Unable to distinguish clinician-guided therapy discontinuations from patient-initiated ones
Exclusion of patients with only one prescription fill may overestimate adherence

Implication

High OAC non-adherence in AF was observed; leaves open whether targeted interventions improve outcomes in prospective trials.

Abstract

Our objectives were to measure long-term adherence to oral anticoagulants (OACs) in patients with atrial fibrillation (AF) and to identify patient factors associated with adherence. Using linked, population-based administrative data from British Columbia, Canada, an incident cohort of adults prescribed OACs for AF was identified. We calculated the proportion of days covered (PDC) as a time-dependent covariate for each 90-day window from OAC initiation until the end of follow-up. Associations between patient attributes and adherence were assessed using generalized mixed effect linear regression models. 30,264 patients were included. Mean PDC was 0.69 (SD 0.28) over a median follow-up of 6.7 years. 54% of patients were non-adherent (PDC < 0.8). After controlling for confounders, factors positively associated with adherence were number of drug class switches, history of stroke or transient ischemic attack, history of vascular disease, time since initiation, and age. Age > 75 years at initiation, polypharmacy (among VKA users only), and receiving DOAC (vs. VKA) were negatively associated with adherence. PDC decreased over time for VKA users and increased for DOAC users. Over half of AF patients studied were, on average, nonadherent to OAC therapy and missed 32% of their doses. Several patient factors were associated with higher or lower adherence, and adherence to VKA declined during therapy while DOAC adherence increased slightly over time. To min im ize the risk stroke, adherence-supporting interventions are needed for all patients with AF, particularly those aged > 75 years, those with prior stroke or vascular disease, VKA users with polypharmacy, and DOAC recipients.