This is the first study to evaluate statin medication adherence and associated outcomes in a diabetic population based on a national Medicaid database. A retrospective claims-based study was conducted in patients who were continuously enrolled in Medicaid from January 2004 to December 2006. Patients (≥ 18 years) with diagnosis of hyperlipidemia and type 2 diabetes were identified by international classification of disease 9th revision (ICD-9) codes based on medical claims. Prescriptions of statin or oral antidiabetic medications were identified by national drug code (NDC) based on drug claims. Demographic, clinical and medication related information was extracted from the MarketScan® Medicaid database. The eligible patients starting the use of statin medications in 2005 were followed for one year to measure medication use, hospitalization, outpatient visits, emergency room (ER) visits, and healthcare costs. A conceptual model based on modified health belief model and health services use behavior model was proposed in this study. Propensity scores were used to remove the imbalance of baseline characteristics between patients with diabetes and without diabetes. Regression models were used to compare mediation adherence and healthcare costs. Multiple linear regression analysis was implemented to assess associations between healthcare costs and statin medication possession ratio (MPR) , while logistic regression analysis was conducted to evaluate associations between medical utilization (hospitalization and ER visit) and likelihood of statin medication adherence (MPR ≥ 0.8).
A total of 7184 eligible patients with hyperlipidemia were included in the study (5479 for non-diabetic group, 1705 for diabetic group). Overall patients with diabetes presented worse health conditions than those without diabetes based on total number of medications used, frequency of outpatient visits, occurrence of hospitalization and ER visit, and severity of comorbidity. Both groups showed poor statin medication adherence rate calculated by MPR that were 0.50 for non-diabetic patients and 0.61 for diabetic patients. Diabetic patients were more likely to be adherent to statin medications (OR = 1.60) and achieved lower hyperlipidemia-related healthcare costs than non-diabetic patients after adjusting for demographic, medical utilization, clinical history, and medication related variables. In diabetic group, age, race, ER visit, and total number of outpatient visits in one year prior to index date were significant predictors to estimate statin medication adherence behavior. Diabetic patients with adherence to statins presented lower risks for hospitalization (OR = 0.80, 95% CI: 0.636, 0.966) and ER visit (OR = 0.71, 95% CI: 0.519, 0.812) and lower medical care costs within one year period.
Statin medication adherence plays an important role to control cholesterol level and reduce medical utilization and costs for diabetic patients enrolled in Medicaid. Early interventions are needed in lipid-lowering treatment. Effective patient education and social service might be considered in medication adherence improvement program in Medicaid enrolled patients with diabetes and comorbid hyperlipidemia.