Real-World Use of Extended Half-Life Factor IX in Children with Haemophilia B

Introduction Limited studies have reported data on the real-world clinical use of extended half-life (EHL) IX products in children and adolescents with haemophilia B, also referred to as people with haemophilia B (PWHB). Aim To examine the real-life experience with EHL factor IX products in PWHB regarding the clinical experience with standard half-life products (SHL). Methods A retrospective review of medical records of PWHB who have been prescribed EHL IX factor concentrates was conducted. Results Fourteen male PWHB were enrolled in the study, all with severe bleeding phenotypes being on prophylaxis (1-6 years old: n = 3, 7-12 years old: n = 5 and 13-18 years old: n = 6). Four of them were previously untreated patients; nine out of fourteen children (64%) had severe, four had moderate, and one child had mild haemophilia B. Median length of follow-up was 45 months (range 16-84 months). Children who transitioned from SHL prophylaxis to EHL prophylaxis experienced changes in their treatment outcomes. The median dosing interval increased from 3.5 days to 7 days, mean trough levels rose from 4.3% to 15.3% among children with severe haemophilia B, and the mean annual bleeding rate (ABR) decreased from 1.8 to 1 (p = 0.3, Wilcoxon test). Significant differences were found in EHL vs. SHL use regarding (a) the factor IX consumption for prophylaxis and bleeds (p = 0.046, t-test), with the EHL consumption (45.6 IU/kg/week) being significantly lower than the SHL consumption (70.3 IU/kg/week), and (b) the factor IX consumption only for prophylaxis (p = 0.022, t-test), with the EHL consumption (37.0 IU/kg/week) being significantly lower than the SHL consumption (66.0 IU/kg/week). There was no inhibitor development. Conclusion This study demonstrates the successful use of EHL prophylaxis in PWHB.