Safety and effectiveness of efgartigimod in patients with generalized myasthenia gravis by autoantibody subtype: analysis of post-marketing surveillance in Japan

Abstract Efgartigimod for intravenous infusion (efgartigimod-IV) is approved in Japan for generalized myasthenia gravis (gMG) regardless of autoantibody subtypes, whereas the approvals in other countries are restricted to only anti-acetylcholine receptor antibody (AChR-Ab) positive. Post-marketing surveillance was conducted in Japan with gMG patients who received efgartigimod-IV from 2022 to 2023. Safety analysis set included 473 patients: 56.7% ( n = 268) AChR-Ab positive, 13.3% ( n = 63) anti-muscle-specific kinase antibody (MuSK-Ab) positive, 29.2% ( n = 138) double-seronegative (AChR-Ab and MuSK-Ab negative), and 0.85% ( n = 4) unavailable. Adverse drug reactions and serious adverse drug reactions were reported in 22.6% and 4.2% of patients. No specific safety signals were observed in any of the autoantibody subtypes. Effectiveness analysis set consisted of 307 patients. After three weeks from the first administration, mean Myasthenia Gravis-Activities of Daily Living (MG-ADL) total score decreased from 7.2 to 4.2: − 3.0 points (standard deviation [SD]: 3.0, p < 0.001). At one-year, mean dose (SD) (mg/day) of oral glucocorticoid decreased from 10.7 to 7.7: − 3.0 mg/day (SD: 6.2, p < 0.001). Similar results were observed across all autoantibody subtypes. In real-world settings, our results demonstrated that efgartigimod-IV was well tolerated and effective in patients with gMG regardless of autoantibody subtypes. Glucocorticoid dosage reduction was observed following efgartigimod initiation.