Chronic obstructive pulmonary disease medication adherence and health outcomes in Medicare beneficiaries

The objectives for this study were to examine adherence to COPD maintenance medications for Medicare beneficiaries with COPD, to examine association between COPD maintenance medication adherence and all-cause hospitalization, and to examine association between COPD maintenance medication adherence and all-cause hospital days. A retrospective cohort study was conducted using data from the Medicare Current Beneficiary Survey. COPD medication adherence was assessed during the six months after an index date, which was defined as the date of first COPD maintenance medication fill following a diagnosis of COPD in the interval from July 1, 2007 through December 31, 2009. Hospitalization was assessed during a six month period following the COPD medication use assessment period. Individuals were included in the sample if they were in the MCBS during 2007, 2008, or 2009, had a diagnosis of COPD, and had Medicare Part D claims on COPD maintenance medications. Individuals were excluded if they had less than two Medicare Part D claims during the COPD medication assessment period, had less than 6 months continuous coverage for Medicare Part D following the COPD medication assessment index date, had less than 6 months continuous coverage before the COPD medication assessment index date or less than 12 months continuous coverage following the COPD medication assessment index date for Medicare Part A or Part B, or resided in a long-term care facility during the COPD medication assessment period. Among 383 beneficiaries who met the study criteria, 44 percent were 75 years or older, 59 percent were female, and 84 percent were White. Medication adherence was assessed by proportion of days covered (PDC). Beneficiaries with a PDC 0.80 or higher were classified as adherent and beneficiaries with a PDC less than 0.80 were classified as nonadherent. Approximately 45 percent of the sample was adherent. The association between medication adherence and all-cause hospitalization was assessed using multivariate logistic regression models, which adjusted for demographic variables age, gender, race, marital status, education, income, region, residence, Medicare status, and clinical variables smoking status, perceived health, influenza vaccine, Charlson Comorbidity Index, individual clinical conditions, prior hospitalization and oxygen use. No association was found between medication adherence and risk of having a hospitalization. The association between medication adherence and all-cause hospital days was assessed using multivariate zero-inflated negative binomial models, which adjusted for the same demographic and clinical covariates listed above. Nonadherent beneficiaries on average had 1.35 more hospital days in comparison to adherent beneficiaries (Average marginal effect=1.35, Standard error=0.59, p=0.023)