Pressurized Metered-Dose Inhaler Versus Dry Powder Inhaler Adherence Among Individuals with Asthma and COPD

<i>Background:</i> The core management of most individuals with asthma and COPD is daily treatment with inhalers such as inhaled corticosteroids (ICS) and long-acting bronchodilators. The two main types of inhalers used are pressurized metered-dose inhalers (pMDIs) and dry powder inhalers (DPIs). Different studies have shown low adherence to inhaler treatments among subjects with asthma and COPD. In this study, we explored the differences in adherence between pMDIs and DPIs of combined ICS and long-acting β₂-agonist inhalers (ICS + LABA) in a large cohort, free from commercial biases. <i>Methods:</i> In this historical prospective study, we included all adult subjects with asthma and/or COPD who acquired at least one ICS + LABA inhaler between 2016 and 2019. We carried out propensity score matching and then compared the maximal number of pMDIs and DPIs purchased in any continuous 12 months during the study period. We also compared once-a-day DPIs with twice-a-day DPIs. <i>Results:</i> Of the 36,998 matched subjects, 5897 (15.9%) purchased pMDIs. The overall median [IQR] inhalers purchased for pMDIs and DPIs were 1 [1, 4] and 3 [1, 8], respectively; for subjects with asthma, 1 [1, 3] and 2 [1, 6]; for subjects with COPD, 1 [1, 3] and 3 [1, 10]; and for subjects with asthma-COPD overlap, 2 [1, 7] and 6 [2, 12]. For all the comparisons, <i>p</i> < 0.001. The once-a-day DPI group had a slight but significantly better adherence than the twice-a-day DPI group. <i>Conclusions:</i> For ICS + LABA therapy, the number of DPIs purchased was significantly greater than the number of pMDIs purchased, as well as the once-a-day DPI relative to the other DPIs. Overall, subjects with asthma and/or COPD had low adherence to all inhalers, with the highest adherence observed among subjects with asthma-COPD overlap.