The relationship between fractional exhaled nitric oxide and asthma symptom scores in patients on mepolizumab

Introduction: Fractional exhaled nitric oxide (FeNO) is a non-invasive measure of Type 2 airways inflammation in asthma. It most closely reflects IL-13 levels, and along with the blood eosinophil count relates to both asthma control and exacerbation risk. FeNO is frequently measured in patients with severe eosinophilic asthma (SEA) on the anti-IL-5 mAb mepolizumab despite the fact that levels have not been shown to significantly change with this treatment, and it remains unknown if FeNO correlates with symptom control in patients receiving this medication. Methods: We identified adult SEA patients treated with mepolizumab at Guy’s Severe Asthma Centre, UK with a minimum of 5 sequential monthly paired FeNO-ACQ measures. We used a statistical mixed effects model to investigate the association between FeNO and Asthma Control Questionnaire (ACQ)-6 in patients on mepolizumab. Adjustments were then made to assess whether the presence of nasal polyposis or treatment with maintenance glucocorticoids altered the findings. Results: 102 patient on mepolizumab generating 1,121 paired FeNO and ACQ-6 observations were analysed. This included 73/102 patients for whom a year of monthly paired measurements could be analysed. Overall, there was no significant association between FeNO and ACQ-6 (p=0.17) in this cohort. Following adjustment for the presence of nasal polyposis and/or maintenance glucocorticoids there was still no evidence of an association (p=0.13). Conclusion: In patients treated with mepolizumab, we saw no association between FeNO levels and ACQ-6 over the course of a year of therapy, limiting the use of FeNO measurement in these patients.