Adherence to Inhaled Corticosteroids and Inflammatory Phenotypes in Asthma

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.

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.

Of 960 phenotyped patients (165 T2-low, 538 possible T2-high, 257 T2-high), 484 were included in the adherence analysis. Adherence did not differ significantly between phenotypes, although patients with T2-low asthma showed a tendency towards lower adherence (0.66) than patients with possible T2-high and T2-high asthma (both 0.74). Across phenotypes, increasing age was associated with higher odds of good adherence (OR 1.25, p <0.001). Among male patients, those with T2-high (OR 0.13, p = 0.022) and possible T2-high (OR 0.14, p = 0.023) phenotypes had lower odds of good adherence than those with T2-low phenotype.

In patients with asthma, adherence to ICS did not differ significantly across inflammatory phenotypes, although patients with T2-low asthma tended to show lower adherence. Among males, adherence varied by phenotype, with T2-high and possible T2-high asthma associated with lower odds of good adherence.