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UBC Theses and Dissertations

Adherence to oral anticoagulants in patients with atrial fibrillation Salmasi, Shahrzad


Objective: The overall aim of this dissertation was to provide a better understanding of adherence to oral anticoagulants (OACs) in patients with atrial fibrillation (AF). Methods: Meta-analysis was used to summarize the current evidence on patients’ adherence. Population-based administrative data of British Columbia (BC) was used to develop a cohort of adults with AF. Random-effects multivariable regression modeling was used to develop and validate a method, called REWarDS, to estimate patient’s individualized daily dose of warfarin and facilitate measurement of adherence to this medication. OAC adherence was measured over follow-up by creating time windows. Group-based trajectory modeling was used to characterize adherence trajectories. Regression analyses were used to identify the factors associated with adherence, and adherence trajectories. Results: Systematic review and meta-analysis found that one year after therapy initiation patients, on average, miss 27% of their doses. REWarDS was found to be accurate with superior performance over current methods for estimating exposure to warfarin. 54% of the patients in the cohort were found to be nonadherent to their OAC, missing, on average, 32% of their doses. The greatest decline in adherence was observed in the first year of therapy. Patients were found to exhibit four distinct long-term adherence trajectories. Being on Vitamin K Antagonist (VKA) was associated with statistically significantly 13% higher adherence compared to being on Direct Oral Anticoagulants (DOAC). Over time, however, adherence increased for DOAC but decreased for VKA. Clinical and demographic factors, while readily available in administrative databases, do not have adequate discriminatory power to predict patients’ adherence trajectories. Conclusion: Adherence in patients with AF was found to be worse than previously understood. Identification of distinct long-term adherence trajectories revealed heterogeneity among nonadherent patients and compels tailoring interventions for different kinds of nonadherence patterns. Findings on the impact of drug class on adherence suggest that prescribers should not assume better adherence for DOACs based on their convenience. Overall, very few variables were identified to be independently associated with any specific adherence trajectory. Altogether, findings call for urgent interventions to improve adherence in patients with AF on both VKA and DOAC, particularly early after therapy initiation.

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