Income-related differences in the use of evidence-based therapies in older persons with diabetes mellitus in for-profit managed care

OBJECTIVES: To determine whether income influences evidence-based medication use by older persons with diabetes mellitus in managed care who have the same prescription drug benefit. DESIGN: Observational cohort design with telephone interviews and clinical examinations. SETTING: Managed care provider groups that contract with one large network-model health plan in Los Angeles County. PARTICIPANTS: A random sample of community-dwelling Medicare beneficiaries with diabetes mellitus aged 65 and older covered by the same pharmacy benefit. MEASUREMENTS: Patients reported their sociodemographic and clinical characteristics. Annual household income (greater than or equal to$20,000 or <$20,000) was the primary predictor. The outcome variable was use of evidence-based therapies determined by a review of all current medications brought to the clinical examination. The medications studied included use of any cholesterol-lowering medications, use of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) for cholesterol lowering, aspirin for primary and secondary prevention of cardiovascular disease, and angiotensin-converting enzyme (ACE) inhibitors in those with diabetic nephropathy. The influence of income on evidence-based medication use was adjusted for other patient characteristics. RESULTS: The cohort consisted of 301 persons with diabetes mellitus, of whom 53% had annual household income under $20,000. In unadjusted analyses, there were lower rates of use of all evidence-based therapies and lower rates of statin use for persons with annual income under $20,000 than for higher-income persons. In multivariate models, statin use was observed in 57% of higher-income versus 30% of lower-income respondents with a history of hyperlipidemia (P = .01) and 66% of higher-income versus 29% of lower-income respondents with a history of myocardial infarction (P = .03). There were no differences by income in the rates of aspirin or ACE inhibitor use. CONCLUSION: Among these Medicare managed care beneficiaries with diabetes mellitus, all of whom had the same pharmacy benefit, there were low rates of use of evidence-based therapies overall and substantially lower use of statins by poorer persons.