The impact of Medicare Part D coverage on medication adherence and health outcomes in end-stage renal disease (ESRD) patients

The purpose of this study was to investigate the impact of Medicare Part D coverage on medication adherence and health outcomes in dialysis patients. A retrospective analysis (2006-2010) using the United States Renal Data System was conducted for Medicare-eligible dialysis patients. Cardiovascular disease morbidity, healthcare utilization and expenditures, medication adherence, and mortality rates were compared, categorized based on patients’ Part D coverage in 2007 for those who: 1) did not reach the coverage gap (cohort 1); 2) reached the coverage gap but not catastrophic coverage (cohort 2); 3) reached catastrophic coverage (cohort 3); and 4) did not reach the coverage gap but received a low-income subsidy (cohort 4). Cox proportional hazards models, Kaplan-Meier methods, logistic regressions, generalized linear models, and generalized estimating equations were used. A total of 11,732 patients were included as meeting inclusion criteria: 1) cohort 1: 3,678 patients had out-of-pocket drug costs <$799; 2) cohort 2: 4,349 patients had out-of-pocket drug costs between $799 and $3,850; 3) cohort 3: 1,310 patients had out-of-pocket drug costs > $3,850; and 4) cohort 4: the remaining 2,395 patients had out-of-pocket drug costs <$799 but received a low-income subsidy. After adjusting for demographic and clinical factors, patients in cohort 2 and cohort 3 had 42 percent and 36 percent increased risk of cardiovascular disease (odds ratio (OR)=1.42, 95% confidence interval (CI):1.20-1.67; OR=1.38, 95% CI:1.10-1.72); and had 36 percent and 37 percent higher death rates compared to those in cohort 4, respectively (hazard ratio (HR)=1.36, 95% CI:1.27-1.44; HR=1.37, 95% CI:1.27-1.48). Patients in cohort 2 were more likely to be nonadherent to medications for diabetes (OR=1.72, 95% CI:1.48-1.99), hypertension (OR=1.69, 95% CI:1.54-1.85), hyperlipidemia (OR=2.01, 95% CI:1.76-2.29), hyperphosphatemia (OR=1.74, 95% CI:1.55-1.95), and hyperparathyroidism (OR=2.08, 95% CI:1.66-2.60) after reaching the coverage gap. These patients had total health care costs that were $2,644 higher due to increased rates of hospitalization and outpatient visits, despite $2,419 lower pharmacy costs compared to patients in cohort 4 after controlling for covariates (p<0.0001). Reaching the Part D coverage gap was associated with decreased medication adherence and unfavorable clinical and economic outcomes in dialysis patients.