JET-GBS - Japanese Eculizumab Trial for GBS

* Patients who have been diagnosed with GBS with reference to GBS NINDS(National Institute of Neurological Disorders and Stroke) diagnostic criteria and those who meet all the following inclusion criteria and do not fall under any of the exclusion criteria will be included in this trial. Inclusion Criteria： 1. Subjects ≥ 18 years of age at the time of obtaining informed consent. 2. Patients with onset of muscular weakness due to GBS less than 2 weeks before the time of consent. 3. Patients unable to walk unaided for ≥5 meters (progressively deteriorating FG(Functional Grade)3 or FG 4-5). 4. Patients who are already on IVIg or deemed eligible for and who will start IVIg (Generally, administration of 400mg/kg over 5 days). 5. Patients who can start their first dose of eculizumab within 2 weeks from onset of weakness and before the end of the IVIg treatment period. 6. Female subjects of child bearing potential with a negative result in their pregnancy test. All subjects must be able to practice an effective, reliable, medically approved method of contraception during the IP(Intraperitoneal) administration period and up to 5 months after IP administration is ended. 7. Patients who can be hospitalized during IP administration period. 8. Patients who have signed the informed consent form. Exclusion Criteria: 1. Patients who are being considered for or are already on plasmapheresis. 2. Patients who are pregnant or lactating. 3. Patients showing clear clinical evidence of peripheral polyneuropathy other than GBS, e.g. diabetic (except for mild sensory disturbance) or severe vitamin B1 deficiency related. 4. Patients who have received immunosuppressive treatment (e.g. azathioprine, cyclosporine, tacrolimus, or \>20 mg prednisolone daily) during the 4 weeks prior to providing consent. 5. Patients who are known to have severe concurrent disease (such as malignancy with uncontrolled primary tumors or metastatic lesions, severe cardiovascular disease, severe COPD(chronic obstructive pulmonary disease ), or TB). 6. Patients who are unable to comply with study procedures and the treatment regimen. 7. Patients who have received rituximab within 24 weeks prior to providing consent. 8. Patients with a history of or unresolved Neisseria meningitides. 9. Patients with active infectious diseases determined to be clinically severe by the principal investigator or sub-investigator that are not being appropriately treated with antibiotics. 10. Patients who that cannot be treated with antibiotic prophylaxis due to allergies. 11. Patients who are allergic to eculizumab. 12. Patients who are known to have or are suspected of having hereditary complement deficiencies. 13. Patients who have been administered another investigational product within 12 weeks prior to providing consent or are currently participating in another trial. 14. Patients with any condition that, in the opinion of the principal investigator or sub-investigator, could increase the patient's risk by participating in the study or confound the outcome of the study. 15. Patients who have a history of Eculizumab treatment for GBS.