INTRODUCTION:Interleukin-5 (IL-5) is the principal cytokine regulating eosinophil growth, differentiation, activation, and expression. It is a specific target of mepolizumab, an anti-IL-5 monoclonal antibody used in the treatment of severe eosinophilic asthma. This new drug can improve symptoms, reduce asthma exacerbations and steroid use. Few data are available on its efficacy for nasal symptoms. OBJECTIVE:To describe the all-round clinical impact of mepolizumab in a real-life setting, evaluating the efficacy and safety of the drug in severe eosinophilic asthma patients. POPULATION AND METHODS:We retrospectively collected the clinical and functional data on 27 patients (16 males) affected with severe eosinophilic asthma, diagnosed at the Siena Regional Referral Centre and monitored for 6 months. Clinical, immunological, and functional data at baseline and follow-up were entered in a database together with comorbidities, number of exacerbations, steroid treatment, multiple-flow exhaled nitric oxide, and validated questionnaires. RESULTS:A significant reduction in asthma exacerbations was observed in all patients after 6 months of the biological therapy (p = 0.0009), and 4/6 patients discontinued chronic oral steroids. A significant improvement in ACT, FEV1, SNOT22, and alveolar nitric oxide was observed after 1 month of mepolizumab (p = 0.003, p = 0.007, p = 0.047, and p = 0.019, respectively) and maintained after 6 months of treatment. After 6 months, FeNO 50 was reduced as well (p = 0.030). Mepolizumab was very well tolerated, and no major side effects were observed. CONCLUSIONS:Our study suggests that mepolizumab is effective in improving control of asthma, lung function parameters, exhaled biomarkers, and nasal symptoms in patients with severe eosinophilic asthma.