C5 and paroxysmal nocturnal hemoglobinuria: The C5 inhibitors eculizumab and ravulizumab are humanized monoclonal antibodies designed to target the complement protein C5, thereby preventing formation of the MAC, release of anaphylatoxin C5a, activation of WBCs and platelets, and lysis of RBCs with the PNH phenotype.40,41 Eculizumab was the first complement inhibitor therapy and the first disease-specific treatment to be approved for patients with PNH by the FDA, EMA, and other regulatory agencies.