Successful switching treatment of mepolizumab for refractory eosinophilic granulomatosis with polyangiitis and multiple organ dysfunction under benralizumab treatment: A case report.

Eosinophilic granulomatosis with polyangiitis (EGPA) is a rare necrotising vasculitis affecting small vessels accompanied by eosinophilic inflammation. Biological therapies, particularly anti-interleukin-5 (IL-5) monoclonal antibodies, have been shown to be effective in treating refractory EGPA. Mepolizumab, an anti-IL-5 monoclonal antibody, has been approved in Japan for the treatment of EGPA and has a significant glucocorticoid-sparing effect. Benralizumab, an anti-IL-5 receptor monoclonal antibody, has also been reported to reduce the glucocorticoid dose in patients with EGPA. However, several investigators have reported the development of EGPA during biologic treatment. Herein, we present a case of development of refractory EGPA under benralizumab treatment. Although the initial treatment with high-dose glucocorticoids and the administration of benralizumab were temporally effective, the patient's condition did not improve, and the eosinophil count reelevated. After switching benralizumab to mepolizumab, the patient's condition improved, and remission was achieved. Our report suggested that mepolizumab may be an effective treatment option for refractory EGPA after failure of benralizumab treatment.