Further, therapeutic strategies need to take into account the delicate balance between suppression of complement-mediated disease pathology and compromise of complement-mediated defense and immunity. After several attempts, several small molecules inhibitors such as compstatin that prevents C3 cleavage, PMX-53 that is a C5aR antagonist are in either preclinical or clinical phases of testing (Qu et al. 2009 ). Only eculizumab (trade name Soliris), which is a humanized monoclonal antibody directed against C5, has been approved by the United States Food and Drug Administration for use in patients with PNH. This antibody prevents the cleavage of C5 to C5a and C5b. The antibody does not seem to activate complement or bind to the host Fc receptor.