Does medication adherence lower Medicare spending among beneficiaries with diabetes?

OBJECTIVE To measure 3-year medication possession ratios (MPRs) for renin-angiotensin-aldosterone system (RAAS) inhibitors and statins for Medicare beneficiaries with diabetes, and to assess whether better adherence is associated with lower spending on traditional Medicare services controlling for biases common to previous adherence studies. DATA SOURCE Medicare Current Beneficiary Survey data from 1997 to 2005. STUDY DESIGN Longitudinal study of RAAS-inhibitor and statin utilization over 3 years. DATA COLLECTION The relationship between MPR and Medicare costs was tested in multivariate models with extensive behavioral variables to control for indication bias and healthy adherer bias. PRINCIPAL FINDINGS Over 3 years, median MPR values were 0.88 for RAAS-I users and 0.77 for statin users. Higher adherence was strongly associated with lower Medicare spending in the multivariate analysis. A 10 percentage point increase in statin MPR was associated with U.S.$832 lower Medicare spending (SE=219; p<.01). A 10 percentage point increase in MPR for RAAS-Is was associated with U.S.$285 lower Medicare costs (SE=114; p<.05). CONCLUSIONS Higher adherence with RAAS-Is and statins by Medicare beneficiaries with diabetes results in lower cumulative Medicare spending over 3 years. At the margin, Medicare savings exceed the cost of the drugs.