Long-term adherence to evidence based secondary prevention therapies after acute myocardial infarction

BACKGROUND: After acute myocardial infarction (AMI), treatment with beta-blockers and angiotensin-converting enzyme inhibitors (ACEI) is widely recognized as crucial to reduce risk of a subsequent AMI. However, many patients fail to consistently remain on these treatments over time, and long-term adherence has not been well described. OBJECTIVE: To examine the duration of treatment with beta-blockers and ACEI within the 24 months after an AMI. DESIGN: A retrospective, observational study using medical and pharmacy claims from a large health plan operating in the Northeastern United States. MEASUREMENT: Enrollees with an inpatient claim for AMI who initiated beta-blocker (N = 499) or ACEI (N = 526) therapy. Time from initiation to discontinuation was measured with pharmacy refill records. Associations between therapy discontinuation and potential predictors were estimated using a Cox proportional hazards model. RESULTS: ACEI discontinuation rates were high: 7% stopped within 1 month, 22% at 6 months, 32% at 1 year and 50% at 2 years. Overall discontinuation rates for beta-blockers were similar, but predictors of discontinuation differed for the two treatment types. For beta-blockers, the risk of discontinuation was highest among males and those from low-income neighborhoods; patients with comorbid hypertension and peripheral vascular disease were less likely to discontinue therapy. These factors were not associated with ACEI discontinuation. CONCLUSION: Many patients initiating evidence-based secondary prevention therapies after an AMI fail to consistently remain on these treatments. Adherence is a priority area for development of better-quality measures and quality-improvement interventions. Barriers to beta-blocker adherence for low-income populations need particular attention.