Male or female patients ≥18 years old

Diagnosis of MG made by the following tests:

1. Positive serologic test for anti-AChR Abs as confirmed at screening, and

2. One of the following:

1. History of abnormal neuromuscular transmission test demonstrated by single-fiber electromyography (SFEMG) or repetitive nerve stimulation, or

2. History of positive anticholinesterase test, e.g. edrophonium chloride test, or

3. Subject has demonstrated improvement in MG signs on oral cholinesterase inhibitors, as assessed by the treating physician.

MGFA Clinical Classification Class II to IV at screening.

MG-ADL total score must be ≥6 at screening and Randomization (Day 1).

Subjects who have:

1. Failed treatment with at least two immunosuppressive agents. Or,

2. Failed treatment with at least one immunosuppressive agent and require chronic plasma exchange or IVIg

Safety and Efficacy of Eculizumab in Refractory Generalized Myasthenia Gravis (REGAIN Study)