Untangling the relationship between medication adherence and post-myocardial infarction outcomes: Medication adherence and clinical outcomes

Background Patients who adhere to medications experience better outcomes than their nonadherent counterparts. However, these observations may be confounded by patient behaviors. The level of adherence necessary for patients to derive benefit and whether adherence to all agents is important for diseases that require multiple drugs remain unclear. This study quantifies the relationship between medication adherence and post-myocardial infarction (MI) adverse coronary events. Methods This is a secondary analysis of the randomized MI FREEE trial. Patients who received full prescription coverage were classified as adherent (proportion of days covered >= 80%) or not based upon achieved adherence in the 6 months after randomization. First major vascular event or revascularization rates were compared using multivariable Cox models adjusting for comorbidity and health-seeking behavior. Results Compared with patients randomized to usual care, full coverage patients adherent to statin, beta-blocker, or angiotensin-converting enzyme inhibitor/angiotensin receptor blocker were significantly less likely to experience the study's primary outcome (hazard ratio [HR] range 0.64-0.81). In contrast, nonadherent patients derived no benefit (HR range 0.98-1.04, P = .01 for the difference in HRs between adherent and nonadherent patients). Partially adherent patients had no reduction in clinical outcomes for any of the drugs evaluated, although their achieved adherence was higher than that among controls. Conclusion Achieving high levels of adherence to each and all guideline-recommended post-MI secondary prevention medication is associated with improved event-free survival. Lower levels of adherence appear less protective.