The purpose of this study is to measure the pharmacokinetics (PK), pharmacodynamics (PD), safety, tolerability, and immunogenicity of efgartigimod PH20 SC in pediatric participants with gMG aged 2 to \<18 years. The primary goal is to confirm an appropriate dose of efgartigimod PH20 SC for pediatric patients using PK and PD results from this study. Participants will receive injections of efgartigimod PH20 SC and will be monitored for safety until the end of the study. At the end of the follow-up period, eligible participants may roll over to an open-label extension (OLE) study.
The participants will be in the study for up to 14 weeks.
The participant (and/or their legally authorized representative) understands the requirements of the study and is capable of providing written informed consent/assent and complying with protocol requirements
The participant is aged 2 to <18 years at the time of informed consent/assent
The participant has been diagnosed with generalised Myasthenia Gravis that is supported by a physical examination and confirmed seropositivity for anti-acetylcholine receptor antibodies
The participant has had an unsatisfactory response to immunosuppressants, corticosteroids, or acetylcholinesterase inhibitors but is on stable concomitant MG therapy. If receiving corticosteroids and/or immunosuppressants, must be on a stable dose for ≥1 month before screening
Is a female adolescent of child-bearing potential who is pregnant and/or lactating or intends to become pregnant during their participation in the study
Has worsening muscle weakness secondary to a concurrent infection or as a result of a medication
Has a documented lack of clinical response to plasma exchange (PLEX)
Received a live or live-attenuated vaccine within <4 weeks before screening