[A CASE OF SEVERE ASTHMA SWITCHED TO MEPOLIZUMAB DUE TO LATE-OCCURRING UNRESPONSIVENESS TO BENRALIZUMAB].

We report the case of a 66-year-old patient with severe asthma complicated by eosinophilic chronic rhinosinusitis (ECRS). The patient was initially treated with benralizumab, which resulted in marked improvement of asthma symptoms and reduced the peripheral blood eosinophil count to 0/μL. Additionally, oral steroids were discontinued. After 7 months of benralizumab administration, the asthma symptoms worsened and peripheral blood eosinophil count increased to 813/μL. The neutralizing antibodies to benralizumab may have resulted in the recurrence of symptoms due to eosinophilic inflammation. The nasal symptoms, on which benralizumab had an unremarkable effect, improved when treatment was switched to mepolizumab. However, the difference in effects of biologics on ECRS has not been elucidated and warrants further investigation. To the best of our knowledge, this is the first report of a case of severe asthma in which mepolizumab administration reversed the clinical deterioration of asthma, which was possibly caused by neutralizing antibodies to benralizumab.