Real-World Adherence to Asthma and COPD Medications in Belgium: A Nationwide Analysis of Determinants Using...

Background/Objectives: Therapeutic adherence to asthma and COPD medications remains worryingly low and varies widely across patient groups, underscoring persistent challenges in chronic respiratory care. The aim of this nationwide study is to quantify real-world adherence and to identify its demographic and clinical determinants using the Belgian health care claims database of the National Institute for Health and Disability Insurance (NIHDI). Methods: Adherence was assessed using the Continuous Multiple Interval Measure of Medication Availability (CMA) among patients treated between 2020 and 2023. Mixed-effects logistic regression was applied to identify determinants of adherence. Results: Only 30.5% of patients achieved good adherence (CMA ≥ 0.8). Adherence varied substantially across pharmacological classes, ranging from 8.1% for inhaled corticosteroids to 66.4% for triple therapy. Age emerged as a major determinant, with adherence increasing steadily across age groups: only 4.0% of children and 15.7% of adolescents reached good adherence, compared with progressively higher rates in adults. Mixed-effects logistic regression confirmed age, sex, and pharmacological class as robust predictors of adherence. Conclusions: These findings highlight the magnitude of the therapeutic adherence gap in chronic respiratory diseases and clearly identify children, adolescents, and ICS or LABA + ICS users as the highest-risk groups. Recognizing these profiles has direct implications for clinical practice, as it provides concrete targets for future patient-centered interventions and guideline-concordant adherence-enhancing strategies.