Interval change in fractional exhaled nitric oxide (FENO) reflects short-term but not long-term change in adherence

Abstract

<b>Background:</b> Short-term improvement in adherence to high dose inhaled corticosteroids (ICS) suppresses fractional exhaled nitric oxide (FENO) in patients with difficult asthma. Whether change in FENO correspondingly reflects longer-term change in adherence is unknown. <b>Aim:</b> Examine how change in adherence over varying time intervals affects FENO in asthma. <b>Method:</b> Using electronic dose monitors (EDM) affixed to patients’ usual ICS inhalers, baseline adherence was established by covert monitoring of ICS use over 1 month. Immediately thereafter, EDM reminders were switched on for 1 week to optimise adherence (‘short-term phase’). EDM reminders were then switched off and adherence monitored over 3 months (‘long-term phase’). FENO was measured at the start and end of each phase. Change in FENO was analysed in relation to change in adherence using linear regression. <b>Results:</b> Forty-two patients completed all visits. At the end of the short-term phase, change in adherence independently predicted change in FENO (β=-0.36, p=0.036) even after adjusting for baseline adherence and ICS dose. The higher the baseline FENO, the greater the decline in FENO with improved adherence. In contrast, change in adherence between the start and end of the long-term phase was not associated with change in FENO. We identified 3 latent groups based on daily adherence patterns in the long-term phase. Two groups with initial adherence &lt;60% and &lt;80%, respectively, had declining adherence over 3 months without significant change in FENO; the third group had persistently high adherence &gt;80% with stable FENO over time. <b>Conclusion:</b> Change in FENO correlates with change in adherence over 1 week but not 3 months.