Real-world outcomes with recombinant factor IX Fc fusion protein (rFIXFc) prophylaxis: Longitudinal follow-up in a national adult cohort

Introduction: In 2017, all people with severe haemophilia B (PWSHB) in Ireland switched from standard half-life (SHL) recombinant FIX (rFIX) to rFIX Fc fusion protein (rFIXFc) prophylaxis. Aims: To evaluate prophylaxis regimens, bleeding rates and factor usage for two years of rFIXFc prophylaxis in a real-world setting.Methods: Data collected retrospectively from electronic diaries and medical records of PWSHB for a two-year period on rFIXFc prophylaxis were compared with paired baseline data on SHL rFIX treatment. Results: 28 PWSHB (≥18 years) were enrolled, and at switchover 79% were receiving prophylaxis and 21% episodic treatment with SHL rFIX. At 24 months following switchover, all remained on rFIXFc prophylaxis with reduced infusion frequency; median dose per infusion once weekly (55 IU/kg, 20/28), every 10 days (63 IU/kg, 2/28) or every 14 days (98 IU/kg, 6/28). Median annualised bleed rate improved significantly on rFIXFc prophylaxis (2.0 versus 3.3 on SHL FIX) (p = 0.01). Median FIX trough level with once-weekly infusions was 0.09 IU/ml (0.06–0.14 IU/ml). Management of bleeding episodes was similar with rFIXFc and SHL rFIX; one infusion was sufficient to treat 74% and 77% of bleeds, respectively, with similar total median treatment per bleeding episode. Factor consumption reduced by 28% with rFIXFc prophylaxis (57 IU/kg/week, range 40–86 IU/kg/week) compared with SHL rFIX (79 IU/kg/week, range 44–210 IU/kg/week) (p = 0.002). Conclusion: This study provides important insights into real-world experience of switching to rFIXFc prophylaxis in an adult population, demonstrating high rates of prophylaxis, with reduced infusion frequency, bleeding and FIX consumption.