Introduction Ravulizumab, an innovative complement C5 inhibitor given every 8 weeks (q8w), was recently demonstrated in a large phase 3 study of patients (pts) with paroxysmal nocturnal hemoglobinuria (PNH) and naive to complement inhibitor therapy to be non-inferior to eculizumab given every 2 weeks (q2w) across all endpoints that measured different aspects of PNH disease (transfusion avoidance [TA], lactate dehydrogenase normalization [LDH-N], percent LDH reduction, breakthrough hemolysis [BTH], Functional Assessment of Chronic Illness Therapy [FACIT]-Fatigue, and hemoglobin stabilization [HGB-S]) (Lee JW et al. EHA Learning Center, Jun 17, 2018; LB2603). PNH pts currently receiving eculizumab may experience treatment burden associated with the q2w dosing regimen. With the development of ravulizumab, PNH pts on prior eculizumab therapy can potentially switch to ravulizumab without interruption of treatment. The primary objective of this study was to assess the noninferiority of ravulizumab compared to eculizumab in adult PNH pts who were clinically stable after having been treated with eculizumab for at least 6 months. Methods In this phase 3, open-label, multicenter study (NCT03056040), adult pts with a documented diagnosis of PNH who were treated with labelled-dose eculizumab for >6 months having LDH levels ≤1.5 times the upper limit of normal at screening were randomly assigned 1:1 to continue eculizumab or switch to ravulizumab. Pts randomized to ravulizumab received weight-based loading [day 1]/maintenance doses [day 15 and q8w thereafter]: ≥40 to Results Of 208 pts screened, 197 pts were randomized (1:1) to ravulizumab or eculizumab, 195 received treatment (ravulizumab, n=97; eculizumab, n=98), and 191 pts completed 183 days of treatment. Pt demographics and baseline clinical characteristics were similar between treatment groups. On average, pts had received prior eculizumab therapy for 5.8 years. All pts received all planned infusions of study medication. Ravulizumab was statistically significantly noninferior to eculizumab for the primary and all key secondary endpoints, with all point estimates favoring ravulizumab: percentage change in LDH levels (difference of -9.21% [95% CI: -18.84, 0.42]), BTH (difference of -5.1 [95% CI -18.89, 8.89]), change in FACIT-Fatigue score (difference of 1.47 [-0.21, 3.15]), TA (difference of 5.5 [95% CI -4.27, 15.68]), and HGB-S (difference of 1.4 [-10.41, 13.31]) (Fig A, Fig B). Superiority testing of the primary endpoint (percentage change in LDH) did not reach statistical significance (P=0.0583 vs P Conclusion Results of this large phase 3 study show that ravulizumab achieved noninferiority compared with eculizumab in pts with PNH on stable eculizumab therapy. Pts can be safely and effectively switched from eculizumab given q2w to ravulizumab given q8w. In pts previously stable on eculizumab, no pts switched to ravulizumab experienced BTH vs 5 pts on eculizumab during the 26-week treatment period. This may be related to optimized ravulizumab dosing compared to eculizumab, resulting in complete and sustained C5 inhibition for all pts. Disclosures Kulasekararaj:Alexion Pharmaceuticals, Inc.: Consultancy, Honoraria, Other: Travel Support . Hill:Apellis: Consultancy, Honoraria; Bioverativ: Consultancy, Honoraria; Regeneron: Consultancy, Honoraria; Akari: Consultancy, Honoraria; Ra Pharma: Consultancy, Honoraria; Alexion Pharmaceuticals, Inc.: Consultancy, Honoraria. Rottinghaus:Alexion Pharmaceuticals, Inc.: Employment, Equity Ownership. Wells:Celgene: Honoraria, Membership on an entity9s Board of Directors or advisory committees; Novartis: Honoraria; Alexion Pharmaceuticals, Inc.: Honoraria, Other: Travel Support , Research Funding. Gonzalez-Fernandez:Alexion Pharmaceuticals, Inc.: Consultancy, Honoraria. Gaya:Alexion Pharmaceuticals, Inc.: Consultancy, Honoraria. Lee:Alexion Pharmaceuticals, Inc.: Consultancy, Honoraria, Research Funding. Ojeda Gutierrez:Alexion Pharmaceuticals, Inc.: Consultancy, Honoraria. Szer:Alexion Pharmaceuticals, Inc.: Consultancy, Honoraria, Other: Travel Support , Research Funding. Risitano:Pfizer Inc.: Membership on an entity9s Board of Directors or advisory committees, Speakers Bureau; Alexion Pharmaceuticals, Inc.: Consultancy, Honoraria, Membership on an entity9s Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis: Consultancy, Honoraria, Membership on an entity9s Board of Directors or advisory committees, Research Funding, Speakers Bureau; Amyndas Pharmaceuticals: Consultancy; Alnylam Pharmaceuticals, Inc.: Consultancy, Honoraria, Research Funding; Jazz Pharmaceuticals: Membership on an entity9s Board of Directors or advisory committees, Speakers Bureau; Ra Pharmaceuticals, Inc.: Consultancy, Honoraria, Research Funding. Nakao:Alexion Pharmaceuticals, Inc.: Consultancy, Honoraria; Kyowa Hakko Kirin Co., Ltd.: Honoraria; Novartis: Honoraria. Bachman:Alexion Pharmaceuticals, Inc.: Equity Ownership, Other: Former employee. Shafner:Alexion Pharmaceuticals, Inc.: Employment, Equity Ownership. Damokosh:Alexion Pharmaceuticals, Inc.: Employment, Equity Ownership. Ortiz:Alexion Pharmaceuticals, Inc.: Employment, Equity Ownership. Roth:Pfizer: Consultancy, Honoraria, Research Funding; Roche: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Alexion Pharmaceuticals, Inc.: Consultancy, Honoraria, Research Funding; Bioverativ: Consultancy, Honoraria; Amgen: Research Funding. Peffault De Latour:Pfizer Inc.: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Alexion Pharmaceuticals, Inc.: Consultancy, Honoraria, Research Funding; Amgen Inc.: Research Funding.