Eculizumab is a monoclonal antibody. Eculizumab binds to proteins in the blood that can destroy red blood cells in people with genetic conditions that affect the natural defenses of red blood cells. Eculizumab is used to prevent the breakdown of red blood cells in people with paroxysmal nocturnal hemoglobinemia (PNH). Eculizumab is also used to treat a rare chronic blood disease called atypical hemolytic uremic syndrome...