Adherence to Antithrombotic Therapy for Patients Attending a Multidisciplinary Thrombosis Service in Canada - A Cross-Sectional Survey

Background: Poor medication adherence puts patients who require antithrombotic therapy at greater risk of complications. We started a multidisciplinary Adult Outpatient Thrombosis Service in 2017 in a Canadian health authority and were interested in the level of medication adherence in the population attending.

Aims: The aim of this study is to assess adherence to antithrombotic medications for patients attending a multidisciplinary Thrombosis Service.

Methods: We conducted a cross-sectional survey of outpatients seen at the Thrombosis Service between 2017 and 2019 using the 12-item validated Adherence to Refills and Medications Scale (ARMS) to assess adherence to antithrombotic (anticoagulants and antiplatelet) therapy. Linear regression analysis examined the factors associated with adherence to antithrombotic therapy.

Results: Of 1058 eligible patients, 53.2% responded to the survey. Seventeen were excluded from the analysis for missing more than 6 responses to the 12 items on the ARMS. About 55% (n = 297) were on direct oral anticoagulants (DOACs), 19% (n = 102) on warfarin, 5.0% (n = 27) on low molecular weight heparin, 3.3% (n = 18) on antiplatelet therapy and 18% (n = 96) were no longer on antithrombotic therapy. Nearly half (47%, n = 253) had taken antithrombotic therapy for 1-5 years while 28% (n = 150) and 25% (n = 137) had taken antithrombotic treatments for <1 and >5 years, respectively. Most patients (87%, n = 475) were ≥50 years and half (51%, n = 277) were male. The mean adherence score was 13.9 (SD±2.2) and 88% (n = 481) of participants were adherent to antithrombotic treatment (ARMS = 12-16). Multivariable linear regression showed that patients with post-graduate education had 0.4% lower adherence to antithrombotic therapy as compared with elementary education (β = 0.0039, p = 0.048). Patients with prior antithrombotic agent use >5 years had 0.5% lower adherence to antithrombotic treatment compared to patients with <1 year (β = 0.0047, p = 0.0244).

Conclusion: Self-reported adherence to antithrombotic therapy was high (88%) within a multidisciplinary Thrombosis Service. Patients with advanced education and prolong duration of antithrombotic therapy were more likely to have lower self-reported adherence to antithrombotic treatment.