Investigating the Association Between Biologic Initiation and Medication Adherence in Severe Asthma: An Analysis of Linked Data

BACKGROUND: Poor adherence to inhaled therapy is common among patients with asthma. Findings from previous studies exploring inhaled corticosteroid (ICS) adherence in biologic-treated populations are inconsistent and have not investigated the long-term outcomes. OBJECTIVE: -agonist (LABA) adherence and to investigate the effect of poor ICS/LABA adherence on clinical outcomes among biologic-treated patients. METHODS: A retrospective cohort study of adults who attended the Northern Ireland Regional Severe Asthma center between September 2015 and November 2021 was performed. Medication possession ratios (MPRs) for ICS/LABA medication were calculated using community dispensing records. Good adherence was defined as an MPR ≥75%. We compared adherence before and after biologic initiation, examined the correlates of adherence, and used multivariable longitudinal models to assess the impact of adherence on asthma outcomes. RESULTS: Of 207 included patients, 58 (28.0%) had suboptimal adherence before biologic initiation. This was associated with higher deprivation (43.1% vs 25.2%; P = .012) and fractional exhaled nitric oxide (50 vs 32 parts per billion; P = .043). Population-level MPRs were stable during the study; however, adherence varied for individual patients. A total of 69 (33.3%) patients had poor adherence 1 year after biologic initiation. Although a substantial reduction in exacerbation rates was seen for both groups after biologic initiation, those with good adherence had an additional 17.4% (95% confidence interval: 2.2%, 30.2%) reduction in exacerbations compared with those with poor adherence. We found no difference in asthma symptoms or lung function. CONCLUSIONS: The introduction of biologics had little impact on population-level adherence; however, there were substantial changes for individual patients. Good adherence to ICS/LABA was associated with lower exacerbation rates among biologic-treated patients with severe asthma.