Assessing the association between medication adherence, as defined in quality measures, and disease-state control, health care utilization, and costs in a retrospective database analysis of Medicare supplemental beneficiaries using statin medications

BACKGROUND: Adherence to medication, and related health and economic outcomes, is becoming increasingly important as populations age and as the number of Americans managing chronic conditions increases. The Pharmacy Quality Alliance (PQA) statin medication adherence measure is used in Medicare star ratings to evaluate health plan performance. Yet, limited evidence exists that investigates the association between statin medication adherence, as specified in the PQA adherence quality measure, and disease-state control, health care utilization, and costs. OBJECTIVE: To determine the association between adherence (≥80% proportion of days covered) and disease-state control, health care utilization, and health care costs for Medicare supplemental beneficiaries using statin medications eligible for inclusion in the PQA statin adherence quality measure. METHODS: This retrospective study used a cohort of eligible beneficiaries for inclusion in the PQA statin adherence measure with low-density lipoprotein (LDL) laboratory values from IBM MarketScan Medicare Supplemental Research Databases (2009-2015). A logistic regression model assessed the association between adherence and LDL control (controlled individuals had LDL levels ≤ 100 mg/ dL). Health care utilization and costs during a 1-year period, from first statin medication claim, were compared between adherent and nonadherent groups using generalized linear models with log link and negative binomial distribution (utilization) or gamma distribution (costs), adjusting for covariates. Beta coefficients were used to compute cost ratios (CR) and rate ratios (RR). Cohort characteristics were assessed using t-tests, Wilcoxon rank sum tests, or chi-square tests. An a priori alpha level of 0.001 was used. RESULTS: The study cohort consisted of 77,174 beneficiaries, of whom 58,668 (76.0%) were classified as adherent to their statin medications. After controlling for other factors, odds of diseasestate control were approximately 2 times higher among medication adherent beneficiaries compared with their nonadherent counterparts (OR = 2.192; 95% CI = 2.109-2.278). Multivariable analyses showed adherers experienced 4.7% fewer outpatient (RR = 0.953; 95% CI = 0.940-0.965) and 27.5% fewer inpatient (RR = 0.725; 95% CI = 0.687- 0.766) visits; had 9.9% lower outpatient (CR = 0.901; 95% CI = 0.885- 0.916) and 28.3% lower inpatient (CR = 0.717; 95% CI = 0.705-0.729) costs; 14.7% lower total costs (CR = 0.853; 95% CI =0.838-0.868); and 7.0% higher prescription drug costs (CR = 1.070; 95% CI = 1.052-1.089) than nonadherers. Adherence to statin medications was associated with a reduction in total costs of $157.32 per member per month. CONCLUSIONS: This retrospective database analysis demonstrated that statin adherence was associated with approximately twice the odds of having a controlled disease state compared with nonadherence in a large Medicare sample. Adherent beneficiaries had fewer outpatient and inpatient visits (lower utilization), lower outpatient and inpatient costs, and lower total costs, a calculated savings of $157.32 per member per month, despite having higher prescription drug costs. Finally, these results provide important new information by demonstrating that adherence (≥ 80%) is associated with lower health care costs in a short (1-year) time frame.