Assessing the Impact of Medication Adherence on Long-Term Cardiovascular Outcomes

Abstract

Background: Although guideline-recommended therapies reduce major adverse cardiovascular events (MACE) in patients after myocardial infarction (MI) or those with atherosclerotic disease (ATH), adherence is poor.

Objectives: The goal of this study was to determine the association between medication adherence levels and long-term MACE in these patients.

Methods: We queried the claims database of a large health insurer for patients hospitalized for MI or with ATH. The primary outcome measure was a composite of all-cause death, MI, stroke, or coronary revascularization. Using proportion of days covered for statins and angiotensin-converting enzyme inhibitors, patients were stratified as fully adherent (≥80%), partially adherent (≥40% to ≤79%), or nonadherent (<40%). Per-patient annual direct medical (ADM) costs were estimated by using unit costs from 2 national files.

Results: Data were analyzed for 4,015 post-MI patients and 12,976 patients with ATH. In the post-MI cohort, the fully adherent group had a significantly lower rate of MACE than the nonadherent (18.9% vs. 26.3%; hazard ratio [HR]: 0.73; p = 0.0004) and partially adherent (18.9% vs. 24.7%; HR: 0.81; p = 0.02) groups at 2 years. The fully adherent group had reduced per-patient ADM costs for MI hospitalizations of $369 and $440 compared with the partially adherent and nonadherent groups, respectively. In the ATH cohort, the fully adherent group had a significantly lower rate of MACE than the nonadherent (8.42% vs. 17.17%; HR: 0.56; p < 0.0001) and the partially adherent (8.42% vs. 12.18%; HR: 0.76; p < 0.0001) groups at 2 years. The fully adherent group had reduced per-patient ADM costs for MI hospitalizations of $371 and $907 compared with the partially adherent and nonadherent groups.

Conclusions: Full adherence to guideline-recommended therapies was associated with a lower rate of MACE and cost savings, with a threshold effect at >80% adherence in the post-MI population; at least a 40% level of long-term adherence needs to be maintained to continue to accrue benefit. Novel approaches to improve adherence may significantly reduce cardiovascular events.

Keywords: atherosclerosis; myocardial infarction; secondary prevention.