ACH-4471 is a potent and highly specific factor D inhibitor nominated as the first compound to be advanced into clinical development. Primary and secondary pharmacology studies, as well as non-clinical toxicity studies up to 28 days, have been completed. ACH-4471 was dosed orally in non-human studies and demonstrated the ability to block the activation of the alternative pathway. ACH-4471 was been shown to substantially decrease hemolysis and C3b deposition on red blood cells from patients with PNH, and achieved dose-dependent inhibition of cell killing in Atypical hemolytic uremic syndrome (aHUS) in the modified HAM assay. Achillion initiated a first-in-human trial with ACH-4471 in February 2016.