Inhaled Corticosteroid Adherence Patterns in a Longitudinal Asthma Cohort

Background: Electronic prescribing records can enable exploration of medication adherence, but analysis decisions may influence estimates and require alignment to new consensus-based definitions. Objective: To compare different computations of inhaled corticosteroid (ICS) implementation in a primary care asthma population initiating ICS therapy when assessed within episodes of persistent use, and examine longitudinal variation in implementation. Methods: A historical cohort study was conducted on UK's Optimum Patient Care Research Database. Eligible patients had physician-diagnosed asthma, initiated ICS therapy, and had 3 or more years of continuous registration. ICS treatment episodes were constructed on the basis of 3 definitions, permitting 30-, 90-, and 182-day gaps between prescriptions. Implementation was estimated using 2 continuous medication availability (CMA I and II) definitions to explore effects of carryover of previous prescriptions in 4 observation windows: 6, 8, 12, and 24 months. Impact of methodology was assessed by descriptive statistics, linear mixed models, and measures of agreement. Results: A total of 13,922 eligible patients (mean age, 39.9 years; 48.7% men) were identified. For CMA I, permitting a 90-day gap, mean ICS implementation for the 2-year period was 89.3% (±16.0%; range, 14.4%-100%). Sensitivity analyses with 30- and 182-day gaps resulted in increased (97.0% ± 7.2%) and decreased (81.1% ± 21.6%) estimates. CMA II produced estimates with varying concordance (0.69-0.87). Substantial variance was found between and within patients (intraclass coefficient, 0.30-0.36). Conclusions: Different analysis choices resulted in substantial variation in implementation estimates, highlighting the need for transparent and clinically relevant methododology. Distinguishing between (non)persistence and implementation is important in clinical practice, and may require different interventions in routine consultations.