Eculizumab is a monoclonal antibody that targets complement protein C5 and inhibits its activation, ultimately preventing the formation of the membrane attack complex (MAC) in the complement system. This drug is used to treat various complement-mediated diseases, such as paroxysmal nocturnal hemoglobinuria (PNH) and atypical hemolytic uremic syndrome (aHUS). Eculizumab has been shown to significantly improve outcomes and quality of life for patients with these conditions by reducing hemolysis, thrombosis, and organ damage. Additionally, research is ongoing to explore the potential use of eculizumab in other complement-mediated diseases and conditions.