AB025. Medication adherence: placing the ‘when’ and ‘which’ in the equation

Background: Medication adherence is a dynamic process and may vary depending on life circumstances and treatment regimens, particularly in health conditions with variable symptoms such as asthma. Yet, adherence is commonly operationalized in observational studies as a single average score, which ignores its dynamic nature. Moreover, current self-report measures often do not assess behaviour nor capture relevant distinct properties of adherence, which reduces their accuracy and usefulness compared to, for example, electronic monitoring. Within a 2-year cohort study on asthma (ASTRO-LAB), we developed a new 6-item self-report tool for assessing adherence to daily inhaled corticosteroids (ICS) and long-acting beta-agonists (LABA) which used only items that capture the different relevant properties of adherence behaviours. We tested its ability to capture suboptimal adherence and variability in adherence for different types of inhaler and in different time intervals.

Methods: Adults and parents of children with asthma (age ≥12 and 6–11) in the United Kingdom (UK) and France answered up to seven 4-monthly computer-assisted telephone interviews (CATIs) conducted by trained interviewers. Respondents specified which inhalers they were prescribed daily and in what dosage, and reported on key elements of inhaler implementation adherence (e.g., dosing per intake; daily dosing; drug holidays), with more detailed questions on shorter time intervals (last day, week, month, and 4 months). We estimated adherence for different time intervals and examined its variation between treatments (Kruskal-Wallis, Wilcoxon) and within and between individuals (multilevel models).

Results: Of the 934 participants interviewed in the baseline CATI, 810 reported being prescribed one daily inhaler [241 ICS, 28 LABA, 541 fixed dose combination (FDC)], 60 participants were prescribed ICS and LABA in separate inhalers, 22 reported FDC simultaneously with ICS or LABA inhalers, and 42 reported none. During follow up, substantial variation in adherence between inhalers was reported, with 1-day, 1-week, 1-month and 4-month scores showing <100% adherence in 34–69% of 3,920 inhalers from 3,634 CATIs. The 6 items targeting different adherence properties showed low to strong associations (P=0.04–0.73). In CATIs in which respondents reported one inhaler, adherence to FDC was higher than to ICS, but not different from LABA [e.g., KWχ2(2)= 16.8, P<0.001; 2,979 CATIs from 817 respondents]. Adherence to ICS and LABA did not differ in CATIs in which respondents had them prescribed as separate inhalers for the past 4 months (W=791.5–1,082.5, P>0.05; 162 CATIs from 62 respondents). Adherence varied between and within participants during the study follow-up (unconditional means models ICC =0.52–0.58). Longitudinal models of adherence predictors and outcomes are currently under development.

Conclusions: Medication adherence is often suboptimal and varies in time, which can be captured by appropriate self-report tools. To understand its role in asthma management, we need to investigate which adherence properties and time intervals are predictive of outcomes under which conditions and for which individuals. Once these properties are identified, understanding their modifiable causes would facilitate the development of more effective self-management interventions in asthma.

Keywords: Medication adherence; asthma; equation; long-acting beta-agonists (LABA); inhaled corticosteroids (ICS)