coagulation factor therapy coagulation factor IX replacement therapy Intravenous infusion with coagulation factor IX. Deficiency of the coagulation cofactor factor IX (FIX) leads to the X‐chromosomal inherited bleeding disorder hemophilia B. Current therapy for hemophilia is based on the infusion of clotting factor concentrates either at the time of bleeding (on demand therapy) or in a prophylactic schedule to prevent bleeding episodes.