Adherence to dual antiplatelet therapy among outpatients after acute myocardial infarction in primary care

Introduction: The efficacy outcomes of dual antiplatelet therapy (DAPT) observed in randomized controlled trials are often not replicated in real-world post-myocardial infarction (MI) patients due to suboptimal adherence to prescribed pharmacotherapy. This study aimed to assess DAPT adherence in outpatients after MI and evaluate its association with risk of major adverse cardiovascular events (MACE). Material and methods: This retrospective pharmacoepidemiologic study included 276 patients who experienced AMI between January 1, 2021, and December 31, 2023, based on electronic medical data. Adherence was measured using proportion of days covered (PDC) metric. Kaplan-Meier curves were constructed to evaluate the impact of DAPT adherence on the incidence of MACE over a 12-month period. Results: Patients primarily received ASA 100 mg (91.3%) in combination with P2Y12 inhibitor ticagrelor (68.5%). The proportion of patients fully adherent to DAPT (PDC≥80% for both components) over 12 months was only 46.4%, with a significant decline from 60.9% to 42.0% between first and second half-year periods (p<0.001). Adherence to P2Y12 inhibitors was significantly higher compared to ASA (87.8±18.9% vs. 73.6±27.5%; p<0.001), largely due to high adherence to ticagrelor (PDC=92.5±12.8%). Post-MI patients fully adherent to DAPT had a lower probability of MACE compared to non-adherent (p=0.047). The protective effect of optimal adherence, adjusted for patient comorbidity, was also assessed using Cox regression, which demonstrated a 2% reduction in MACE risk for every 1% increase in PDC (p<0.05). Conclusion: Higher adherence to DAPT following MI was associated with lower risk of MACE. However, adherence declined over time, underscoring the necessity of enhancing medication adherence in post-MI outpatients.