The primary purpose of this study is to characterize the pharmacokinetics and pharmacodynamics of treatment with ravulizumab intravenous infusion in pediatric participants with gMG.

Inclusion Criteria:

• Diagnosis of gMG confirmed by a positive serologic test for anti-AChR antibodies (Abs) obtained at Screening and/or during Screening Period
• Myasthenia Gravis Foundation of America (MGFA) Clinical Classification of Class II to Class IV at Screening
• Participants receiving treatment must be on a stable dosing regimen of adequate duration prior to Screening and during the Screening Period.
• Eculizumab-experienced participants must have been enrolled and treated with eculizumab in Study ECU-MG-303 for at least 6 months (180 days) and must have been on a stable dose for ≥ 2 months (60 days) prior to Screening.
• All participants must be vaccinated against meningococcal infection

Exclusion Criteria:

Medical Conditions

• Any untreated thymic malignancy, carcinoma, or thymoma.
• Participants with a history of treated benign thymoma
• History of thymectomy, thymomectomy, or any thymic surgery within the 12 months prior to Screening
• History of N meningitidis infection
• Known to be human immunodeficiency virus (HIV) positive
• History of unexplained infections
• Known or suspected history of drug or alcohol abuse or dependence within 1 year prior to the start of the Screening Period

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