Association between inhaler device type and therapeutic adherence in Belgium: a retrospective cohort study

Background Despite its importance for asthma and COPD outcomes, therapeutic adherence remains suboptimal. Evidence largely focuses on dry powder and pressurised metered‑dose inhalers (DPIs and pMDIs) in corticosteroid‑based therapies, with limited data on other devices and pharmacological classes. Methods We conducted a retrospective cohort study using dispensing data from the Belgian Independent Health Insurance Funds. Adults aged 19–80 years with ≥ 2 dispensations of ICS‑, LABA‑ or LAMA‑based mono‑, dual‑ or triple therapy between 2020 and 2023 were included. Adherence was measured using CMA3, calculated for each patient–device–class combination and dichotomised at CMA ≥ 0.8. Mixed‑effects logistic regression models with patient‑level random intercepts were used. Results A total of 77,237 patients contributed to CMA3 exposures. DPIs showed higher adherence (41.4%) than pMDIs (32.5%) and nebulizers (13.1%). SMIs showed the highest adherence (48.6%) but were limited to LAMA and LABA/LAMA therapies. In adjusted analyses, inhaler device type remained independently related to adherence. DPIs showed higher odds of adherence than pMDIs in the main model (OR 1.64; 95% CI 1.57 1.71). In the restricted LABA/LAMA model, DPIs also showed higher adherence than SMIs (OR 4.65; 95% CI 4.25–5.09). This pattern was consistent across all pharmacological classes. Conclusions Inhaler device type is associated with therapeutic adherence. Across therapeutic classes, DPIs were associated with higher adherence than pMDIs and SMIs. Device choice should be considered alongside inhaler training to improve adherence.