The humanized monoclonal antibody eculizumab (Soliris®) is a complement 
inhibitor indicated for use in anti-acetylcholine receptor (AChR) 
antibody-positive adults with generalized myasthenia gravis (gMG) in the USA, 
refractory gMG in the EU, or gMG with symptoms that are difficult to control 
with high-dose IVIg therapy or PLEX in Japan. It is the first complement 
inhibitor to be approved for use in these patients. In the well-designed, 
26-week REGAIN study in patients with anti-AChR-positive refractory gMG, 
although a statistically significant benefit of eculizumab over placebo in the 
prespecified primary endpoint analysis (change from baseline in MG-activities of 
daily living (ADL) score assessed by worst-rank ANCOVA) was not formally 
demonstrated, preplanned and post hoc sensitivity analyses of this outcome, as 
well as other secondary outcomes supported the efficacy of eculizumab. Overall, 
patients receiving eculizumab experienced significant improvements in the ADL, 
muscle strength and health-related quality of life (HR-QOL) parameters relative 
to patients receiving placebo. Moreover, an ongoing extension of REGAIN showed 
that treatment benefits with eculizumab were sustained during continued therapy 
for at least 52 weeks. Eculizumab was generally well tolerated in these studies, 
with a tolerability profile similar to that reported previously in other 
indications. Although several questions remain, such as duration of treatment, 
cost effectiveness and long-term efficacy and tolerability, current evidence 
indicates that eculizumab is a valuable emerging therapy for patients with 
refractory gMG.