Use of direct oral anticoagulants in patients with atrial fibrillation in Scotland: applying a coherent framework to drug utilisation studies

Purpose: To report the use of direct oral anticoagulants (DOAC) for stroke prevention in patients with atrial fibrillation (AF) in Scotland and advocate the standardisation of drug utilisation research methods. Methods: Retrospective cohort study using linked administrative data. Patients included those with a diagnosis of AF (confirmed in hospital) who received a first prescription for a DOAC (dabigatran, rivaroxaban, apixaban) from September 2011 to June 2014. Drug utilisation measures included discontinuation, persistence, and adherence. Results: 5398 patients (mean CHA2DS2-VASc score 2.98 [SD 1.71], 89.7% with ≥ 6 concomitant medicines) were treated with DOACs for a median of 228 days (IQR 105 – 425). Of 35.6% who discontinued DOAC treatment, 11.0% switched to warfarin and 48.3% re-initiated DOACs. Persistence after 12 and 18 months were 75.9% and 69.8%, respectively. Differences between individual DOACs were observed: discontinuation rates ranged from 20.4% (apixaban) to 60.6% (dabigatran), and 12 months persistence from 60.1% (dabigatran) to 85.5% (apixaban). Adherence to treatment with all DOACs was good: overall DOAC median medication refill adherence (MRA) was 102.9% (IQR 88.9% – 115.5%), and 82.3% of patients had an MRA > 80%. Conclusions: In Scotland, adherence to DOAC treatment was good and switching from DOAC to warfarin was low. However, discontinuation and persistence rates were variable – although treatment interruptions were often temporary. To decrease the inconsistencies in drug utilisation methods and facilitate meaningful study comparison, the use of a coherent framework – using a combination of discontinuation, persistence and adherence – and the standardisation of measurements is advocated.