Long‐term safety and efficacy of rIX‐FP prophylaxis with extended dosing intervals up to 21 days in adults/adolescents with hemophilia B

BACKGROUND: An international, multicenter extension study evaluated recombinant fusion protein linking recombinant coagulation factor IX (FIX) with recombinant human albumin (rIX‐FP) in hemophilia B (FIX ≤ 2%) patients previously enrolled in a phase III study or who initiated rIX‐FP prophylaxis following surgery. OBJECTIVES: To investigate the long‐term safety and efficacy of rIX‐FP prophylaxis in adult previously treated patients (PTPs) with hemophilia B. METHODS: Male PTPs were treated with a 7‐ (35‐50 IU/kg), 10‐ or 14‐day regimen (50‐75 IU/kg). Patients ≥18 years who were well‐controlled on a 14‐day regimen for ≥6 months could switch to a 21‐day regimen (100 IU/kg). RESULTS: A total of 59 patients (aged 13‐63 years) participated in the study. Following a single dose of 100 IU/kg rIX‐FP, in patients eligible for the 21‐day regimen, the mean terminal half‐life was 143.2 hours. Mean steady‐state FIX trough activity levels ranged from 22% with the 7‐day regimen to 7.6% with the 21‐day regimen. Median (Q1, Q3) annualized spontaneous bleeding rates were 0.00 (0.00, 1.67), 0.28 (0.00, 1.10), 0.37 (0.00, 1.68), and 0.00 (0.00, 0.45) for the 7‐, 10‐, 14‐, and 21‐day regimens, respectively. Comparable efficacy was demonstrated for both the 14‐ and 21‐day regimens compared to the 7‐day regimen. Overall, 96.5% of bleeding episodes were treated successfully with 1 to 2 rIX‐FP infusions. No patients developed an inhibitor and treatment was well tolerated. CONCLUSIONS: rIX‐FP extended interval prophylaxis provides dosing flexibility and, in selected patients, a 21‐day regimen may provide an alternative option to minimize treatment burden and individualize treatment.