Spontaneous Bleeding and Poor Bleeding Response with Extended Half-life Factor IX Products: A Survey of Select US Hemophilia Treatment Centers
ISTH Academy. Sidonio R. Jul 10, 2019; 273953; OC 70.4 Topic: FVIII/IX
Robert Sidonio
Robert Sidonio
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OC 70.4

Spontaneous Bleeding and Poor Bleeding Response with Extended Half-life Factor IX Products: A Survey of Select US Hemophilia Treatment Centers

L.M. Malec1, S.E. Croteau2, M. Callaghan3, R. Sidonio4
1Versiti Blood Research Institute, Milwaukee, United States, 2Boston Chidren's Hospital, Boston, United States, 3Children's Hospital of Michigan, Detroit, United States, 4Emory / Children's Healthcare of Atlanta Comprehensive Hemophilia Program, Atlanta, United States

Main Topic: Coagulation and Anticoagulation
Category: FVIII/IX

Background: Factor IX (FIX) has significant distribution to the extravascular space and binding to type IV collagen which is important in hemostasis, but not quantifiable in clinical practice for patients receiving FIX replacement. Among the pivotal trials of extended half-life factor IX products (EHL-FIX), FIX plasma trough activity were widely ranging with a narrow range of bleeding rates suggesting trough value alone may not predict bleeding.
Aims: To characterize the use and performance of EHL-FIX in clinical practice at four U.S. hemophilia treatment centers (HTCs).
Methods: An electronic survey regarding center specific use of EHL-FIX amongst patients with severe hemophilia B (SHB) was sent in fall 2018. Providers were asked if patients utilizing EHL-FIX had experienced 1) spontaneous/minimally traumatic bleeding events at factor levels >10% or 2) poorly controlled bleeding events requiring more frequent/higher doses of EHL-FIX than anticipated in addition to patterns of EHL-FIX product switching.
Results: Surveyed HTCs cared for 71 patients with SHB including 55 (77%) who utilized EHL-FIX, 24 (34%) recombinant factor IX (FIX) albumin fusion protein (rFIX-FP) and 31 (44%) recombinant factor IX Fc fusion protein. No patients received glycopegylated recombinant FIX. Unexpected spontaneous/minimally traumatic bleeding and poorly controlled bleeding were reported in 13 patients, all using rFIX-FP prophylaxis (Table 1). Six patients have discontinued use of EHL-FIX based on shared decision making with providers (Table 2).
Conclusions: Although plasma FIX activity levels have driven prophylaxis and bleed management decisions, clinical experience suggests novel properties of EHL-FIX may impact hemostasis. Successful bleed prevention or control in SHB may be predicted by the distribution of FIX in circulation and extravascular space, and the presence of FIX in tissues at time of injury. These data demonstrate the importance of real-world monitoring of efficacy of new FIX products and suggest the need for more robust mechanisms to understand the hemostatic performance of products.

  Center 1 Center 2 Center 3 Center 4
Total patients with severe hemophilia B 19 18 24 10
Patients who have received EHLs
rFIX-FP 8 4 7 5
rFIXFc 7 4 18 2
rFIX-GP 0 0 0 0
Patients with unexpected bleeding or poorly controlled bleeding events
rFIX-FP 4 3 4 2
rFIXFc 0 0 0 0
rFIX-GP n/a n/a n/a n/a
[Table 1: Center-specific data regarding use of EHL-FIX products amongst patients with SHB]

  Center 1 Center 2 Center 3 Center 4
rFIX-FP to different EHL 2 0 3 0
rFIX-FP to a SHL 2 3 0 1
rFIXFc to a different EHL 0 1 0 0
rFIXFc to a SHL 0 0 0 0
rFIX-GP to a different EHL n/a n/a n/a n/a
rFIX-GP to a SHL n/a n/a n/a n/a
[Table 2: Patterns of product switching amongst patients receiving EHL-FIX]

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