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An Open-Label, Single-arm Study to Evaluate the Pharmacokinetics (PK), Pharmacodynamics (PD), Safety, and Efficacy of Gefurulimab in Pediatric Patients (6 to < 18 years of age) with Generalized Myasthenia Gravis (gMG) Who Express Acetylcholine Receptor Antibodies (AChR+) (PK, PD, Safety, and Efficacy Study of Gefurulimab in Pediatric Patients with AChR+ Generalized Myasthenia Gravis)

PK, PD, Safety, and Efficacy Study of Gefurulimab in Pediatric Patients with AChR+ Generalized Myasthenia Gravis (PK, PD, Safety, and Efficacy Study of Gefurulimab in Pediatric Patients with AChR+ Generalized Myasthenia Gravis)

Terada Michinori

Alexion Pharma GK

Tamachi Station Tower N, 3-1-1, Shibaura, Minato-ku, Tokyo 108-0023, Japan

JPDept-DevOps-PMCO@alexion.com

Terada Michinori

Alexion Pharma GK

Tamachi Station Tower N, 3-1-1, Shibaura, Minato-ku, Tokyo 108-0023, Japan

+81-3-3457-9559

JPDept-DevOps-PMCO@alexion.com

Recruiting

Jan. 30, 2026

Interventional

single arm study

open(masking not used)

uncontrolled control

single assignment

treatment purpose

Participants who have a documented diagnosis of gMG over or equal to 3 months (90 days) prior to Screening based on clinical disease features and at least 1 of the following confirmatory tests. Test results may be collected from participant records or obtained during Screening:
> Positive response in an acetylcholinesterase inhibitor test, for example, the edrophonium chloride test
> Abnormal neuromuscular transmission demonstrated by repetitive nerve stimulation or single fiber electromyography
> Previous improvement of symptoms or signs related to gMG during treatment with on oral acetylcholinesterase inhibitor, as confirmed by the treating physician
Positive serological test for AChR autoantibodies (previous test results, if applicable, must be confirmed at Screening by central laboratory).
MGFA Class II to IV at Screening and on Day 1.
Must have QMG total score as outlined below:
> Participants 12 to < 18 years of age must have QMG total score over or equal to 12 at Screening and on Day 1
> Participants 6 to < 12 years of age will have no minimum QMG total score required for inclusion; however, participants must have documented limb weakness in at least 1 limb

Clinical features that, in the opinion of the Investigator, are consistent with a Clinical Deterioration including myasthenic crisis, under or equal to 28 days prior to Screening or during the Screening Period.
Any medical condition (eg, cardiac, pulmonary, renal, oncologic, neurological or psychiatric disorder) or risk factor that, in the opinion of the Investigator or the Medical Monitor, might interfere with participation in the study, pose any added risk to the participant, or confound the assessment of safety or efficacy of the study intervention.
History of thymectomy or any other thymic surgery within 6 months prior to screening.
Any untreated thymic malignancy, carcinoma, or thymoma.

Generalized Myasthenia Gravis

Gefurulimab(Integral combination product: biological product and device)

To characterize the PK and PD of treatment with gefurulimab in pediatric participants with AChR+ gMG

To evaluate safety of gefurulimab in pediatric participants with AChR+ gMG
To assess the efficacy of gefurulimab in pediatric participants with AChR+ gMG
To assess immunogenicity of gefurulimab in pediatric participants with AChR+ gMG for the duration of the study

Yes

Alexion has a public commitment to allow requests for access to study data and will be supplying a protocol, CSR, and plain language summaries.

United States/Brazil/Taiwan/Poland