Long-term efficacy and safety of rIX-FP prophylaxis in adult patients with haemophilia B on a 21-day dosing regimen

Objective The introduction of factor replacement products with enhanced half-life has helped patients with haemophilia B to overcome one of the limitations of standard factor IX (FIX) products by allowing less frequent infusions. rIX-FP is one such FIX product, that provides a prolonged dosing interval in patients with haemophilia B. A phase III extension study evaluated the long-term efficacy and safety of rIX-FP prophylaxis in adult patients with haemophilia B, including a subset of patients treated on a 21-day dosing regimen.

Material and Methods During the phase III clinical trial, patients with severe haemophilia B (FIX ≤2%) received episodic treatment or routine prophylaxis with rIX-FP. Patients who initially received episodic treatment were switched to a 7-day regimen with rIX-FP (35–50 IU/kg); dosing intervals could then be changed at any 6-month follow up. After 6 months, patients could extend to a 10- or 14-day interval (50–75 IU/kg), if well controlled on the 7-day regimen. During the extension study, patients ≥18 years could extend to a 21-day regimen (100 IU/kg) if well controlled on a 14-day regimen for ≥6 months.

Results A total of 11 patients switched to a 21-day regimen (Figure 1). The mean (SD) monthly consumption of rIX-FP was lower on the 21-day regimen (146.9 [5.53] IU/kg) compared with the 7-day (178.7 [24.63] IU/kg) and 14-day regimens (166.6 [6.21] IU/kg). These 11 patients had a median annualised spontaneous bleeding rate (AsBR) of 0.0 while on prophylaxis throughout the study program; during their time on the 21-day dosing regimen, 64% (7/11) of patients reported zero spontaneous bleeding episodes and the median AsBR was 0.0 (range: 0.0–4.7). After 6 months of treatment on the 21-day regimen, two patients switched back to the 14-day regimen due to breakthrough bleeding. Ten patients reported a total of 29 adverse events over four years; the majority (89.7%) were reported as mild/moderate in intensity with one (peritonsillar abscess) considered severe, and all were unrelated to rIX-FP treatment. No inhibitors, anaphylactic reactions or thromboembolic events were reported.

Conclusion Prophylaxis with rIX-FP on a 21-day dosing regimen demonstrated good efficacy and safety in a selected subset of patients with haemophilia B.

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Publication History

Article published online:
18 June 2021