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.