Reduction in FeNO on anti-IL5 biologics is associated with clinical remission of severe asthma

<bold>Background:</bold> Fractional exhaled nitric oxide (FeNO) is considered a marker of IL13 drive in severe asthma; however, a reduction in FeNO on anti-IL5 biologics is seen in some patients. Currently, the influence of biomarker responder profiles on response to biological treatment is not well understood. <bold>Methods:</bold> We identified bionaive patients in the Danish Severe Asthma Register who received mepolizumab, reslizumab, or benralizumab for at least 12 months. Patients without baseline and follow-up FeNO measurements were excluded. Patients with FeNO ≥ 25 ppb at baseline and a decrease of 10 ppb or 20 % if baseline FeNO ≥ 50 ppb at follow-up were categorised as FeNO responders, and those with baseline FeNO ≥ 25 ppb and no decrease at follow-up were categorised as FeNO non-responders. We then assessed remission at follow-up (no exacerbations, no maintenance oral corticosteroids, ACQ ≤ 1.5, and FEV1 ≥80 % of predicted) in each group. <bold>Results:</bold> At baseline, 66% (265/403) of patients commenced on an anti-IL5 biologic had elevated FeNO: Among these patients 151 (57 %) were FeNO responders, and 114 (43%) were FeNO non-responders at follow-up. FeNO responders had higher FeNO levels at baseline than FeNO non-responders (65 vs. 40 ppb, p<0.0001). A larger proportion of FeNO responders achieved clinical remission after 12 months of treatment than FeNO non-responders (32 % vs. 18 %, p=0.05). <bold>Conclusion:</bold> FeNO response on anti-IL5 biologics was common in a nationwide cohort of asthma patients, and more FeNO responders achieved remission. Biomarker response profiles could guide future treatment strategies aimed at inducing remission with biological treatments.