Study Design and Participants

Participants who completed the 6‐month, double‐blind REGAIN study could enter this extension study. Full inclusion and exclusion criteria for the REGAIN study have been published previously.14 In brief, adults (aged ≥18 years) with the following were eligible for REGAIN: confirmed gMG with positive serology for acetylcholine receptor antibodies, an MG Activities of Daily Living (MG‐ADL) total score of 6 or higher, and failed treatment with 2 or more ISTs or at least 1 IST with requirement for chronic IVIg or plasma exchange therapy over the preceding 12 months. Patients were excluded if they had a history of thymoma or other thymic neoplasm, had undergone thymectomy in the 12 months before screening, experienced ocular‐only MG symptoms (Myasthenia Gravis Foundation of America [MGFA] class I) or myasthenic crisis (MGFA class V) at screening, or required treatment with IVIg or plasma exchange within the 4 weeks before randomization.14

Eligible patients who elected to continue into the open‐label extension were required to enter it within 2 weeks of completing REGAIN. The first patient was enrolled on November 12, 2014, and the last patient was enrolled on March 4, 2016. Participants received open‐label eculizumab until it was otherwise available to them, up to a maximum of 4 years in the extension study. The study was completed in January 2019.

All patients provided written, informed consent. Written approval for the study protocol and all study amendments was obtained from independent ethics committees or institutional review boards at all participating sites. All human studies were approved by the appropriate ethics committee and have been performed in accordance with the ethical standard laid down in the 1964 Declaration of Helsinki.