C5 and paroxysmal nocturnal hemoglobinuria: Ravulizumab is an IgG2/4k monoclonal antibody that specifically binds to the complement protein C5, thereby inhibiting its cleavage at C5a (the proinflammatory anaphyllotoxin) and C5b (the subunit that initiates the membrane attack complex [MAC or C5b‐9]) and preventing the formation of the C5b‐9 complex for the treatment of PNH and atypical hemolytic uremic syndrome in children and adults.