Effectiveness and safety of mepolizumab in combination with corticosteroids in patients with eosinophilic granulomatosis with polyangiitis

Background Mepolizumab (MPZ), an anti-interleukin-5 antibody, is effective for the treatment of eosinophilic granulomatosis with polyangiitis (EGPA). However, its effectiveness has not been adequately evaluated in real-world clinical practice. In this study, we assessed the effectiveness and safety of MPZ (300 mg) for relapsing/refractory EGPA resistant to corticosteroids (CS) for 1 year in real-world settings. Methods We administered MPZ (300 mg) to 16 patients with relapsing/refractory EGPA resistant to CS (Post-MPZ). We also retrospectively collected data from the same patients for the 12 months before the administration of MPZ (Pre-MPZ). The primary endpoint was the 12-month remission rate after MPZ administration and the secondary endpoints were the Birmingham vasculitis activity score (BVAS), vasculitis damage index (VDI), eosinophil counts, changes in concomitant CS doses/concomitant immunosuppressant use, MPZ retention rate, and incidence of adverse events. The clinical course was compared between Pre-MPZ and Post-MPZ. Results The 12-month remission rate after the initiation of MPZ was 75%. No change was observed in BVAS, eosinophil count, or concomitant CS dose over time in the Pre-MPZ group, whereas all these parameters were significantly decreased over time in the Post-MPZ group. The number of patients using concomitant immunosuppressant also decreased over time in the Post-MPZ group. VDI did not increase in either group. The MPZ retention rate was 100% and only three patients (18.8%) had infections. Changes in BVAS, eosinophil count, and cumulative concomitant CS dose were significantly lower in the Post-MPZ group than in the Pre-MPZ group. There was no significant difference in the changes in VDI between the groups. Conclusion This study demonstrated that MPZ is effective and safe for EGPA. Furthermore, MPZ decreases disease activity, increases remission rate, and has a CS-sparing effect.