Medication Use Behavior and Outcomes among Chronic Obstructive Pulmonary Disease Patients

Objectives: (1) Characterize the Chronic Obstructive Pulmonary Disease (COPD) patients and estimate medication adherence (2) Estimate the association between medication adherence and exacerbation risk and COPD-related costs (3) Develop and validate a risk equation to identify medication non-adherence among COPD patients.

Methods: The study used Truven commercial and claims encounter database to identify COPD patients initiating maintenance therapy identified over a 12 month identification period (January 1, 2011 to Dec 31, 2011). The initiation of maintenance medication therapy was classified as the index date. After a 12-month baseline period (January 1, 2010 to Dec 31, 2010), beneficiaries were followed over a two year rolling index period through to December 31, 2013. Medication adherence was assessed using proportion of days covered (PDC). The association of adherence with exacerbations and healthcare expenditure were estimated using logistic regression and γ generalized linear models, respectively, adjusting for socio-demographics, comorbidities, comedication use and proxy measures of disease severity. Risk factors were added to a logistic regression model employing a backward elimination process to develop the final model. Sensitivity, specificity, false positive and false negative rates were specified for the final model. Model performance was also described using c-statistic, percent concordant pairs and percent discordant pairs. To estimate the predictive validity of the final model, the final selection of variables were added in a GLM model and predicted adherence rates were estimated assuming a normal distribution of PDC scores.

Results: Only 58% of newly diagnosed COPD patients were adherent (PDC>0.80) in the first year of maintenance medication use and the adherence rates fell down to 28% (PDC>0.80) during the second year. After controlling for baseline exacerbation rates and healthcare expenditure, patients with PDC <0.80 exhibited higher risk of exacerbations (OR = 1.55, 95% CI: 1.35 – 1.79) and higher total ($784.06) and pharmacy expenditure ($543.12), compared with patients with PDC ≥0.80. Medical expenditure was not different across adherent and non-adherent patients with a new diagnosis of COPD. : The final model included 13 variables which were below the inclusion p-value criteria of p<0.35 and had a c-statistic of 0.799. The newly developed model had a specificity of 81.70% and a sensitivity of 75.20% with a 79.60% concordance in the final model. The concordant validity of the final model was estimated by predicting out adherence values using the final model.The model estimated the adherence level in the COPD population at 55.84% as compared to the actual adherence level of 61.85%.

Conclusions: Only 1 in 4 COPD patients remained adherent to maintenance medication treatment during the second year. Improved adherence in the first year of maintenance therapy use was significantly associated with reduced risk of exacerbation and lower healthcare expenditure. Findings suggest need to identify barriers associated with continued maintenance medication use among newly diagnosed COPD patients. Using information available from healthcare claims data only, predictive models can reliably identify COPD medication non-adherence. Prior medication adherence was the best predictor of the future medication adherence among COPD patients.