Aptevo Therapeutics Inc. announced that the company has begun dosing patients in a Phase 4 clinical trial to evaluate the safety and efficacy of IXINITY(R) [Coagulation Factor IX (Recombinant)] in previously treated patients under 12 years of age with hemophilia B. Launched in the United States in 2015 and wholly-owned by Aptevo, IXINITY is an intravenous recombinant factor IX therapeutic for use in people 12 years of age or older with hemophilia B, a hereditary bleeding disorder characterized by a deficiency of clotting factor IX in the blood. According to the World Federation of Hemophilia 'Report on the Annual Global Survey 2017' approximately 34% of people treated for hemophilia B in the U.S. are 12 years of age or younger. A subset of clinical data from the Phase 3 program to support the registration of IXINITY in the U.S. was previously presented by Aptevo. This analysis was drawn from pooled data of 2 prospective, multi-center, non-randomized, open-label studies of 12 children with hemophilia B under the age of 12 years. The data showed that IXINITY appeared to be well tolerated in this pilot subject population and had results comparable to those from the overall patient population studied in the Phase 3 clinical trial of IXINITY. The current Phase 4 clinical trial is expected to enroll up to 22 patients to evaluate the safety, efficacy, pharmacokinetics and immunogenicity of IXINITY over a period of at least 50 exposure days in patients with hemophilia B who are younger than 12 years of age.