Ravulizumab is a monoclonal antibody used in the treatment of certain complement-mediated diseases, specifically paroxysmal nocturnal hemoglobinuria (PNH). Ravulizumab targets complement protein C5, preventing its cleavage into C5a and C5b by the enzyme C5 convertase. This inhibition prevents the formation of the membrane attack complex (MAC), which is part of the body's immune response. In PNH, the absence of membrane proteins that normally protect red blood cells from the complement system leads to their destruction. Ravulizumab helps to inhibit this process and reduce hemolysis (destruction of red blood cells). It is indicated for the treatment of adult patients with PNH. PNH is a rare acquired disorder characterized by the destruction of red blood cells, leading to symptoms such as hemolytic anemia, fatigue, and blood clots.