AbstractCurrently, eculizumab is the main effective treatment for paroxysmal nocturnal hemoglobinuria (PNH). The aim of this randomized multicenter noninferiority study was to evaluate the efficacy and safety of the Biosimilar (Elizaria) in comparison with the Originator (Soliris) in patients with PNH. Biosimilar and Originator were administered at a dose of 600 mg weekly for 4 weeks at the initial stage in naive patients, as well as for maintenance therapy at a dose of 900 mg every 2 weeks in all patients. The primary endpoint was a comparative assessment of hemolytic activity based on the area under the lactate dehydrogenase (LDH) concentration–time curve during the maintenance therapy. Thirty-two (32) patients were randomized for therapy with Biosimilar (n = 16) or Originator (n = 16). The mean values of LDH concentration–time curve were similar in both treatment groups without statistically significant differences (p > 0.05). Evaluation of secondary endpoints has shown no statistically significant differences between the groups. Safety values were comparable in both treatment groups. The data obtained confirm that the Biosimilar is not inferior to the Originator in terms of the main efficacy parameter, and is also comparable with it in terms of safety and additional efficacy parameters. Clinicaltrials.gov identifier: NCT04463056