Antiparkinson Drug Adherence and Its Association with Health Care Utilization and Economic Outcomes in a Medicare Part D Population

Objectives: We examine the associations of adherence to antiparkinson drugs (APDs) with health care utilization and economic outcomes among patients with Parkinson's disease (PD). Methods: By using 2006-2007 Medicare administrative data, we examined 7583 beneficiaries with PD who filled two or more APD prescriptions during 19 months (June 1, 2006, to December 31, 2007) in the Part D program. Two adherence measures-duration of therapy (DOT) and medication possession ratio (MPR)-were assessed. Negative binomial and gamma generalized linear models were used to estimate the rate ratios (RRs) of all cause health care utilization and expenditures, respectively, conditional upon adherence, adjusting for survival risk, sample selection, and health-seeking behavior. Results: Approximately one-fourth of patients with PD had low adherence (MPR < 0.80, 28.7%) or had a short DOT (<400 days, 23.9%). Increasing adherence to APll therapy was associated with decreased health care utilization and expenditures. For example, compared with patients with low adherence, those with high adherence (MPR = 0.90-1.00) had significantly lower rates of hospitalization (RR = 0.86), emergency room visits (RR = 0.91), skilled nursing facility episodes (RR = 0.67), home health agency episodes (RR = 0.83), physician visits (RR = 0.93), as well as lower total health care expenditures (-$2242), measured over 19 months. Similarly, lower total expenditure (-$6308) was observed in patients with a long DOT versus those with a short DOT. Conclusions: In this nationally representative sample, higher adherence to APDs and longer duration of use of APDs were associated with lower all-cause health care utilization and total health care expenditures. Our findings suggest the need for improving medication-taking behaviors among patients with PD to reduce the use of and expenditures for medical resources.