Eculizumab is a monoclonal antibody aimed at against the complement protein C5 developed by Alexion Pharmaceuticals, Inc. This antibody obstructs the cleavage of C5 and halts the process of complement-mediated cell destruction. Eculizumab has been shown to be effective in treating paroxysmal nocturnal hemoglobinuria. Background Paroxysmal nocturnal hemoglobinuria arises from a somatic mutation of the PIG-A gene in a hematopoietic stem cell and the subsequent production of blood cells with a deficiency of surface proteins that protect the cells against attack by the complement system. The clinical efficacy of eculizumab was tested as showing a humanized antibody that inhibits the activation of terminal complement components, in patients with PNH.

Eleven transfusion-dependent patients with PNH received infusions of Eculizumab every week for four weeks, followed one week later by a 900-mg dose and then by 900 mg every other week through week 12. Clinical and the biochemical indicators of hemolysis were measured throughout the trial.

Mean lactate dehydrogenase levels decreased from 3111 IU per liter before treatment to around 594 IU per liter during treatment (P=0.002). The mean percentage of PNH type III erythrocytes increased from 36.7 percent of the total erythrocyte population to about 59.2 percent (P=0.005). The mean and median transfusion rates decreased from 2.1 and 1.8 units per patient per month to 0.6 and 0.0 units per patient per month, respectively. Episodes of hemoglobinuria were reduced by 96 percent and measurements of the quality of life improved significantly.

Eculizumab is very safe and well tolerated in patients with PNH. This antibody against the terminal complement protein C5 reduces intravascular hemolysis, hemoglobinuria, and the need for transfusion, with an associated improvement in the quality of life in patients with PNH.