C5 and paroxysmal nocturnal hemoglobinuria: Ravulizumab is a second-generation complement component 5 (C5) inhibitor (C5i) approved for the treatment of paroxysmal nocturnal hemoglobinuria (PNH) following positive results from two pivotal trials in patients with PNH originally naive to C5i treatment and eculizumab-experienced patients with PNH.