Safety and effectiveness of efgartigimod for intravenous infusion in patients with generalized myasthenia gravis: an interim analysis of Japanese post-marketing surveillance

Efgartigimod for intravenous infusion (efgartigimod-IV) is approved in Japan for generalized myasthenia gravis (gMG). Post-marketing surveillance was mandated by regulatory authorities to assess the safety and effectiveness of efgartigimod in patients with gMG. Patients with gMG who received efgartigimod-IV between May 2022 and September 2023 were registered. The interim analysis data were cutoff in June 2024 and included patients whose institutions agreed to publication. The safety analysis set consisted of 373 patients: 53.35% (<i>n</i> = 199) anti-acetylcholine receptor antibody positive, 14.21% (<i>n</i> = 53) anti-muscle-specific receptor kinase antibody positive, and 31.64% (<i>n</i> = 118) double-seronegative. Adverse drug reaction and serious adverse drug reaction were reported in 21.45% (80/373) and 4.29% (16/373) of patients, respectively. Although six deaths were reported, none of them were related to efgartigimod. The effectiveness analysis set consisted of 246 patients. After three weeks from the first administration, mean score of MG-Activities of Daily Living decreased from 7.5 to 4.4: −3.1 points improvement (standard deviation: 2.95, <i>p</i> &lt; 0.001). No remarkable differences were observed in the response to efgartigimod between the subgroups of patient baseline characteristics, e.g. autoantibody profiles. In real-world settings, efgartigimod-IV was well tolerated and effective in patients with gMG.