Adherence to Inhaled Corticosteroids and Inflammatory Phenotypes in Asthma

Background and aim: Adherence to inhaled corticosteroids (ICS) is essential for asthma control, yet little is known about whether adherence differs across inflammatory phenotypes. Patients with type 2 (T2)-low biomarkers have reduced corticosteroid responsiveness, which may influence adherence. We aimed to evaluate adherence to ICS across inflammatory phenotypes and to examine whether associations between adherence and clinical risk factors differ by inflammatory phenotype. Material and methods: This retrospective cohort study included adult asthma patients managed at a respiratory outpatient clinic between May 2020 and May 2022. Inflammatory phenotype was defined using blood eosinophils (cut-off 0.15×109/L) and FeNO (cut-off 25 ppb). Patients were categorized into T2-low (two negative T2-biomarkers), possible T2-high (one positive T2-biomarker), and T2-high (two positive T2-biomarkers). Adherence was calculated as medication possession ratio (MPR), with >0.8 defining good adherence. Data was obtained from electronic health records and national registries. Logistic regression models adjusted for relevant covariates were performed.