A Phase 3 Open-Label Study of Eculizumab in Pediatric Participants With Refractory Generalized Myasthenia Gravis (gMG)

Inclusion Criteria:

* Male or female pediatric participants 6 to \<18 years of age at time of assent/consent.
* Vaccinated against Neisseria meningitidis.
* Documented vaccination against Haemophilus influenzae and Streptococcus pneumoniae infections prior to dosing as per local and country specific immunization guidelines for the appropriate age group.
* Diagnosis of MG confirmed by positive serologic test for anti-acetylcholine receptor antibodies at Screening, and 1 of the following: (a) history of abnormal neuromuscular transmission test demonstrated by single-fiber electromyography or repetitive nerve stimulation; (b) history of positive anticholinesterase test (for example, edrophonium chloride or neostigmine test); or (c) participant demonstrated improvement in MG signs on oral acetylcholinesterase inhibitors, as assessed by the Investigator.
* Presence of refractory gMG, defined as participants with gMG who have 1 or more of the following: (a) failed treatment ≥1 year with at least 1 immunosuppressive therapies (IST), defined as follows: (1) persistent weakness with impairment of activities of daily living; (2) myasthenia gravis (MG) exacerbation and/or crisis while on treatment; or (3) intolerance to ISTs due to side effect or comorbid condition(s). (b) Require maintenance plasma exchange (PE) or intravenous immunoglobulin (IVIg) to control symptoms; and/or (c) in the opinion of the Investigator, MG poses a significant functional burden despite current MG treatment.
* MGFA Clinical Classification of Class II to IV at Screening.
* In patients aged 12 to 18 years, QMG total score ≥ 12 at Screening; in patients aged 6 to 11 years, no minimum QMG is required for inclusion; however, patients must have documented limb weakness in at least one limb.
* All MG-specific treatment has been administered at a stable dosing regimen of adequate duration prior to Screening.

Exclusion Criteria:

* Parent or legal guardian is an Alexion employee.
* Any active or untreated thymoma. History of thymic carcinoma or thymic malignancy unless deemed cured by adequate treatment with no evidence of recurrence for ≥5 years before Screening.
* History of thymectomy within 12 months prior to Screening.
* Are pregnant or lactating.
* Any unresolved acute, or chronic, systemic bacterial or other infection, which is clinically significant in the opinion of the Investigator and has not been treated with appropriate antibiotics.
* Use of PE within 4 weeks prior to first dose.
* Use of rituximab within 6 months prior to first dose.
* Patients who are under 15 kg and are receiving maintenance IVIg.
* Participation in another interventional treatment study or use of any experimental therapy within 30 days before initiation of study drug on Day 1 in this study or within 5 half-lives of that investigational product, whichever is greater.
* Have previously received treatment with eculizumab or other complement inhibitors.