Japanese subject subpopulation analysis of B-LONG: a Phase 3 study of long-acting recombinant factor IX Fc fusion protein

The multinational Phase 3 B-LONG study demonstrated the prolonged half-life of recombinant factor IX Fc fusion protein (rFIXFc) versus native recombinant factor IX (rFIX), and the safety and efficacy of rFIXFc for treatment of bleeding and routine prophylaxis in subjects with hemophilia B. This post hoc subgroup analysis of B-LONG evaluated the safety, efficacy, and pharmacokinetics of rFIXFc in Japanese subjects. Previously treated males with moderately severe to severe hemophilia B (endogenous FIX ≤2 IU/dL) received weekly prophylaxis (starting at 50 IU/kg/week, with dose adjustment), individualized interval prophylaxis (starting at 100 IU/kg every 10 days, with interval adjustment), episodic treatment, or perioperative management with rFIXFc. Primary endpoints were annualized bleeding rates (ABRs) and safety. rFIXFc pharmacokinetics were comparable between Japanese subjects (n=6) and non-Japanese subjects. Median ABRs for Japanese subjects in the weekly prophylaxis (n=4) and individualized interval prophylaxis (n=2) groups were 3.27 and 4.28, respectively, which were within the range for non-Japanese subjects. For Japanese subjects, most (95.8%) bleeding episodes were resolved with 1 or 2 rFIXFc infusions, and no treatment-related adverse events or inhibitors were observed. rFIXFc was safe and efficacious for prophylaxis and treatment of bleeding in Japanese subjects with outcomes and pharmacokinetics comparable to non-Japanese subjects.