The influence of Adherence to inhaled Corticosteroids (ICS) on treatment Response to mepolizumab treatment in severe Eosinophilic asthma

<bold>Background:</bold> Poor adherence to ICS in severe eosinophilic asthma patients is associated with poor disease control. Primary objective To evaluate the influence of ICS adherence on mepolizumab treatment responses in patients with severe eosinophilic asthma. <bold>Methods:</bold> We conducted a retrospective study among adult severe eosinophilic asthma patients initiated on mepolizumab treatment. The ICS adherence was determined using a prescription possession ratio (PPR) ≥75% and mepolizumab response per NICE criteria of a 50% reduction in asthma exacerbations and/or a 50% reduction from baseline maintenance oral corticosteroid dose. <bold>Results:</bold> Of 164 participants included in the analysis, 132 (80%) had a positive response to mepolizumab treatment (mean age 53 (13) years, 55% females). Patients with positive mepolizumab response had a lower median number of asthma exacerbations than negative responders during the mepolizumab treatment [1 (0,2) vs 4 (1,6), respectively, p=0.002]. Poor ICS adherence was significantly more common in the negative responders 9/16(56%) than in the positive responders 19/98 (19%), p=0.001. Patients with poor ICS adherence had significantly higher most recent and highest FeNO levels compared to adherent patients with a median FeNO level of [54 ppb (27,78) vs 33 ppb (20,57), p=0.03] and median FeNO levels of [74 ppb (48,108) vs 47 ppb (25,84), p=0.01], respectively. <bold>Conclusions:</bold> Poor ICS adherence was associated with a negative response to mepolizumab treatment. Poor ICS adherence is also associated with a raised FeNO level compared to good ICS adherence. Optimum ICS adherence is required to improve mepolizumab treatment response and patient outcomes.