Long‐Term Safety and Efficacy of Mepolizumab in Eosinophilic Granulomatosis With Polyangiitis

Objectives Eosinophilic granulomatosis with polyangiitis (EGPA) is a rare, relapsing, inflammatory disease. Management of EGPA predominantly relies on oral corticosteroids (OCS), which are associated with many adverse effects. The Phase III MIRRA trial demonstrated efficacy and safety of mepolizumab, anti‐interleukin‐5 biologic, for EGPA. This open‐label extension (OLE) of MIRRA assessed long‐term safety and OCS‐sparing effects of mepolizumab. Methods The OLE (NCT03298061) was a multicenter study that enrolled patients from MIRRA who required OCS ≥5 mg/day up to 6 months after the end of MIRRA. All patients received mepolizumab 300 mg subcutaneously every 4 weeks plus standard‐of‐care until mepolizumab was discontinued or became approved and re‐imbursed for EGPA in the respective country. Key outcomes included adverse events (AEs) and use of OCS. Results One hundred patients were enrolled in the OLE. Mean (standard deviation) and median (min, max) exposure during OLE was 38.5 (27.0) and 27.0 (1.0, 89.0) months. On‐treatment AEs were experienced by 98% of patients (43% treatment‐related; most frequent: injection‐site reaction [10%]) and serious AEs by 38% of patients (6% treatment‐related) with no new safety signals versus MIRRA identified. Median (Q1, Q3) OCS dose decreased from 10.0 (7.8, 15.0) mg/day at OLE baseline to 5.0 (0.0, 10.0) mg/day at study exit. Proportion of patients using OCS >7.5 mg/day decreased from 75% at baseline to 32% at study exit; 28% of patients discontinued OCS. Conclusion Long‐term use of mepolizumab to treat EGPA was well tolerated and resulted in sustained reductions in OCS use.