Objective:

To assess the safety and effectiveness of efgartigimod for intravenous infusion (efgartigimod-IV) in patients with generalized myasthenia gravis (gMG) by serological profiles in real-world settings.

Background:

Efgartigimod is a human IgG1 Fc-fragment engineered to block the neonatal Fc receptor. Efgartigimod-IV is approved in Japan for gMG regardless of serological profiles, i.e., anti-acetylcholine receptor antibody positive (AChR-Ab+), anti-muscle-specific receptor kinase antibody positive (MuSK-Ab+) or double seronegative; anti-LRP4 antibody is not usually tested. Upon the direction by Japan regulatory authorities, post-marketing surveillance (PMS) is performed.

Design/Methods:

Patients with gMG who received efgartigimod-IV between May 2022 and September 2023 were registered for the PMS. Effectiveness was evaluated by Myasthenia Gravis Activities of Daily Living (MG-ADL) total score.

Results:

The safety analysis set consisted of 469 patients: 57.1% (n=268) AChR-Ab+, 13.4% (n=63) MuSK-Ab+, and 29.4% (n=138) double-seronegative. Overall, adverse drug reactions and serious adverse drug reactions were reported in 22.6% and 4.2% of patients, respectively. Generally, safety was consistent with the known safety profile of efgartigimod, and no specific signals were observed in any of the serological profiles. The effectiveness analysis set consisted of 307 patients with a similar composition ratio of serological profiles to the safety analysis set. Overall, mean MG-ADL total score decreased from 7.2 to 4.2 after three weeks from the first administration: −3.0 points (standard deviation: 2.98, p< 0.001). Significant score decreases were observed in each serological profile; −3.0 for AChR-Ab+, −3.7 for MuSK-Ab+, and −2.8 for double-seronegative. For oral glucocorticoid dose, the percentage of patient with ≤5 mg/day increased from 27.7% to 40.8%, and that with >15 mg/day decreased from 15.5% to 7.3% during one year treatment. Substantial oral glucocorticoid dose changes were observed regardless of serological profiles.

Conclusions:

In real-world settings, efgartigimod-IV was well tolerated and effective in patients with gMG regardless of serological profiles: AChR-Ab+, MuSK-Ab+, and double-seronegative.