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Long-term safety and sustained efficacy for up to 5 years of treatment with recombinant factor IX Fc fusion protein in subjects with haemophilia B: Results from the B-YOND extension study.

  • Pasi, K John1
  • Fischer, Kathelijn2
  • Ragni, Margaret3
  • Kulkarni, Roshni4
  • Ozelo, Margareth C5
  • Mahlangu, Johnny6
  • Shapiro, Amy7
  • P'Ng, Stephanie8
  • Chambost, Hervé9
  • Nolan, Beatrice10
  • Bennett, Carolyn11
  • Matsushita, Tadashi12
  • Winding, Bent13
  • Fruebis, Joachim14
  • Yuan, Huixing15
  • Rudin, Dan14
  • Oldenburg, Johannes16
  • 1 Royal London Haemophilia Centre, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London, UK.
  • 2 Van Creveldkliniek, University Medical Center, Utrecht, Netherlands. , (Netherlands)
  • 3 Hemophilia Center of Western Pennsylvania, University of Pittsburgh, Pittsburgh, PA, USA.
  • 4 Michigan State University, East Lansing, MI, USA.
  • 5 Hemocentro UNICAMP, University of Campinas, Campinas, Brazil. , (Brazil)
  • 6 Haemophilia Comprehensive Care Centre, Faculty of Health Sciences, University of the Witwatersrand, and Charlotte Maxeke Johannesburg Academic Hospital and National Health Laboratory Service, Johannesburg, South Africa. , (South Africa)
  • 7 Indiana Hemophilia & Thrombosis Center, Inc., Indianapolis, IN, USA. , (India)
  • 8 The Haemophilia and Haemostasis Centre, Fiona Stanley Hospital, Murdoch, WA, Australia. , (Australia)
  • 9 Children's Hospital La Timone, and Aix Marseille University, INSERM, INRA, C2VN, Marseille, France. , (France)
  • 10 Children's Health Ireland at Crumlin, Dublin, Ireland. , (Ireland)
  • 11 Emory University School of Medicine, Aflac Cancer and Blood Disorders Center of Children's Healthcare of Atlanta, Atlanta, GA, USA.
  • 12 Nagoya University Hospital, Nagoya, Japan. , (Japan)
  • 13 Sobi, Stockholm, Sweden. , (Sweden)
  • 14 Bioverativ, a Sanofi company, Waltham, MA, USA.
  • 15 Sanofi, Waltham, MA, USA.
  • 16 Institute of Experimental Haematology and Transfusion Medicine, University Clinic Bonn, Bonn, Germany. , (Germany)
Published Article
Haemophilia : the official journal of the World Federation of Hemophilia
Publication Date
Nov 01, 2020
DOI: 10.1111/hae.14036
PMID: 32497409


Recombinant factor IX Fc fusion protein (rFIXFc) has demonstrated efficacy for treatment of haemophilia B in the Phase 3 B-LONG and Kids B-LONG studies. However, long-term rFIXFc safety and efficacy data have not yet been reported. To report long-term rFIXFc safety and efficacy in subjects with haemophilia B. B-YOND (NCT01425723) was an open-label extension for eligibl previously treated subjects who completed B-LONG or Kids B-LONG. Subjects received ≥1 treatment regimen: weekly prophylaxis (WP), individualized interval prophylaxis (IP), modified prophylaxis or episodic treatment. Subjects could switch regimens at any time. The primary endpoint was inhibitor development. Ninety-three subjects from B-LONG and 27 from Kids B-LONG (aged 3-63 years) were enrolled. Most subjects received WP (B-LONG: n = 51; Kids B-LONG: n = 23). For subjects from B-LONG, median (range) treatment duration was 4.0 (0.3-5.4) years and median (range) number of exposure days (EDs) was 146 (8-462) EDs. Corresponding values for paediatric subjects were 2.6 (0.2-3.9) years and 132 (50-256) EDs. No inhibitors were observed (0 per 1000 subject-years; 95% confidence interval, 0-8.9) and the overall rFIXFc safety profile was consistent with prior studies. Annualized bleed rates remained low and extended-dosing intervals were maintained for most subjects. Median dosing interval for the IP group was approximately 14 days for adults and adolescents (n = 31) and 10 days for paediatric subjects (n = 5). B-YOND results confirm the long-term (up to 5 years, with cumulative duration up to 6.5 years) well-characterized safety and efficacy of rFIXFc treatment for haemophilia B. © 2020 The Authors. Haemophilia published by John Wiley & Sons Ltd.

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