FeNO variations and clinical response to biological drugs in severe asthma: A retrospective analysis

<bold>Background:</bold> Patients with severe asthma (SA) often present with a type-2 high (T2) inflammation endotype, characterized by an elevated blood eosinophil count (BEC) and a fractional exhaled nitric oxide (FeNO)>25 ppb. However, the response in terms of FeNO variation after treatment with any biological drug can be quite variable. In this retrospective study, we aimed to explore the relationship between clinical and functional outcomes and the changes of FeNO values after 6 months of treatment in patients with SA. <bold>Patients and methods:</bold> We evaluated patients with SA from our records and analyzed relevant demographical, clinical, and functional data collected at baseline and after six months from the beginning of treatment. We defined two groups: FeNO decliners, FD, in which FeNO had dropped at least by 20% at follow-up, and FeNO non-decliners, FND. <bold>Results:</bold> 97 patients (males 50, 51.55%) were included in the final analysis. At follow-up, overall FeNO values were reduced in comparison to baseline, FEV1% increased, and the asthma control test (ACT) score improved significantly (p always < 0.001). When comparing FD with FND, no significant difference was found at baseline nor at follow-up in lung function and BEC, while the FD presented with an overall lower score in ACT after treatment (p = 0.032). When patients were stratified by therapy, no difference between FD and FND was found in all the main outcomes, except for the dupilumab subgroup, where lung function improved significantly more in the FD group. <bold>Conclusions:</bold> Our study underscored that variations in FeNO values at 6 months are mostly independent from the clinical efficacy of the administered biological drug therapy.