COPD medication adherence and quality of life

The association between medication adherence and health-related quality-of-life (HRQoL) in COPD remains poorly understood. Different ways to deal with methodological challenges to estimate this association have probably contributed to conflicting results. This study investigated the association between adherence and HRQoL, thereby illustrating methodological challenges that need to be addressed. We used longitudinal patient-level data from a cluster-randomized controlled trial (i.e. RECODE) including three-year data on type and dose of COPD maintenance medication prescribed and HRQoL (CCQ, SGRQ, EQ-5D) of 511 patients. A linear mixed model was used to assess the association between adherence and HRQoL using a fixed cut-off of 80% of the proportion of days covered (PDC) to define adherence. Subsequently, we investigated the impact of correcting for differences in demographics, disease severity, lifestyle, and previous HRQoL, and using different definitions of adherence. In unadjusted analyses, and analyses adjusting for demographics only, SGRQ score was worse in the adherent compared to the non-adherent group. This association disappeared when correcting for disease severity and/or lifestyle. A better SGRQ score was predictive of decreased adherence in the following year. Accounting for the previous HRQoL did not result in positive associations between adherence and HRQoL. When defining four categories of adherence, patients with a PDC between 80-99% had a significantly worse SGRQ score compared to patients with a PDC<60%, even after correction for lifestyle. There was no significant association between adherence and CCQ or EQ5D. A positive association of adherence and HRQoL was not found, even after adjusting for demographics, lifestyle, disease severity, and previous HRQoL.