Objectives The study investigated dual antiplatelet therapy (DAPT) patterns over time and patient characteristics associated with the various treatments in a myocardial infarction (MI) population.

Design A registry-based observational cohort study was performed using antecedent data.

Setting This study linked morbidity, mortality and medication data from Danish national registries.

Participants All 28 449 patients admitted to a Danish hospital with a first-time MI and alive at discharge from 2009 through 2012 were included.

Primary and secondary outcome measures Primary outcome was initiation of DAPT and secondary outcomes comprised persistence in DAPT treatment and switches between DAPT treatments.

Results The overall proportion of patients prescribed DAPT increased from 68% (CL 95% 67–69%) to 73% (CL 95% 72–74%) from 2009 to 2012. For treatment of patients with and without percutaneous coronary intervention (PCI), the corresponding numbers were from 87% (CL 95% 86–88%) to 91% (CL 95% 90–92%) and from 49% (CL 95% 47–50%) to 52% (CL 95% 51–54%), respectively. Non-PCI patients had a higher cardiovascular risk compared with PCI patients. Among PCI patients, age>75 years, atrial fibrillation, diabetes and peripheral arterial disease were associated with a higher risk of treatment breaks for DAPT. Among patients without PCI, ticagrelor treatment was associated with an increased risk of treatment breaks during the first 12 months compared with clopidogrel treatment.

Conclusions From 2009 to 2012, there was an increase in the proportion of patients with MI receiving DAPT, and a longer duration of DAPT. Still, a large proportion of patients without PCI are discharged either without DAPT or with a short DAPT duration. These findings may indicate the need for more careful attention to DAPT for patients with MI not undergoing PCI in Denmark.