IMPACT OF ORAL ANTICOAGULANT CLASS ON ADHERENCE IN PATIENTS WITH ATRIAL FIBRILLATION: A 23-YEAR POPULATION-BASED COHORT STUDY IN CANADA

Abstract

<h3>BACKGROUND</h3> Studies measuring OAC adherence in AF patients have suffered from short follow-up times, inability to account for frequent medication switches and have excluded warfarin. Our objective was to compare AF patients' long-term adherence between OACs and identify the impact of taking direct oral anticoagulants (DOAC) versus vitamin K antagonists (VKA) on adherence, while accounting for switching. <h3>METHODS AND RESULTS</h3> Using linked, population-based administrative data containing physician billings, hospitalization and prescription records of 4.8 million British Columbians (1996-2019), incident adult cases of AF were identified. Primary measure of adherence was proportion days covered (PDC). Consecutive rolling windows of 90 day in length were created for each patient starting from their first OAC prescription fill date until the end of their follow-up time. PDC for each of the 90-day-long rolling windows were calculated. If a person permanently discontinued their medication, they were given a PDC of 0 for all subsequent rolling windows after their last supply ran out, until the end of their follow-up period. As such, both poor execution and non-persistence were measured simultaneously. Patient's average adherence over follow-up was obtained by calculating the mean of PDC values of all their windows during follow-up. Changes in adherence over time and the association between drug class and adherence were assessed using generalized mixed effect linear regression model with both adherence and drug class treated as time-varying covariates. Study sample comprised of 30,264 AF patients [mean age: 72.2(SD11.0), 44.6% Female] with mean follow-up of 7.7(4.8) years. A majority were initiated on warfarin (69.7%), with mean CHA2DS2-VASc score of 2.94 (SD1.4). Mean PDC for our cohort was 0.71(SD0.27) with 51% considered non-adherent (PDC < 0.8). 40.20% of the cohort experienced OAC switches, most of them being between-class switches. Adherence dropped over time with the greatest decline in the first two years after therapy. After controlling for all other confounders, taking VKA compared to DOAC was, on average, associated with a 1-day decrease in number of days of medication taking per year. <h3>CONCLUSION</h3> Adherence to OACs in patients with AF was well below the conventional threshold of 80%, with less than half of the patients taking these medications as prescribed. Adherence dropped over time, particularly in the first two years after therapy initiation. Switching was common. Drug class had no meaningful impact on medication adherence.