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HTRS2025.P1.3 Abstract of Distinction Clinical Outcomes Over 3 Years of Once-Weekly Efanesoctocog Alfa Treatment in Adults and Adolescents from North America with Severe Hemophilia A in the Phase 3 XTEND-ed Long-Term Extension Study
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HTRS2025.P1.3 Abstract of Distinction Clinical Outcomes Over 3 Years of Once-Weekly Efanesoctocog Alfa Treatment in Adults and Adolescents from North America with Severe Hemophilia A in the Phase 3 XTEND-ed Long-Term Extension Study

Janice Staber, Angela Weyand, Jennifer Dumont and Davide Matino
Research and practice in thrombosis and haemostasis, Vol.9(Supplement 3), pp.103023-103023
11/2025
DOI: 10.1016/j.rpth.2025.103023
url
https://doi.org/10.1016/j.rpth.2025.103023View
Published (Version of record) Open Access

Abstract

Background: Efanesoctocog alfa (formerly BIVV001) is a first-in-class high-sustained factor VIII (FVIII) replacement therapy designed to decouple FVIII from endogenous von Willebrand factor. In the Phase 3 XTEND-1 study (NCT04161495), once-weekly efanesoctocog alfa demonstrated superior bleed protection over prior FVIII prophylaxis, was well tolerated, and provided FVIII activity within the normal to near-normal (>40%) range for most of the week. Objectives: To present data from the second interim analysis of the long-term safety and efficacy of efanesoctocog alfa in adults and adolescents with severe hemophilia A from North America in the XTEND-ed study (NCT04644575). Methods: Previously treated patients (≥12 years) who completed XTEND-1 could continue efanesoctocog alfa (50 IU/kg, once-weekly) prophylaxis in the multicenter, open-label, long-term XTEND-ed study (Arm A). The primary endpoint is incidence of FVIII inhibitor development (determined by the Nijmegen modified Bethesda assay). Secondary endpoints include annualized bleed rates (ABRs), efficacy for bleed treatment, and safety. Data cut: February 22, 2024. Results: The North America subgroup consisted of 20 participants (including 1 female) who rolled over from XTEND-1 to Arm A of XTEND-ed (age: 12–17 years, n=5; 18–64 years, n=14; ≥65 years, n=1). The median (range) treatment duration in XTEND-ed was 112.4 (44.1–136.6) weeks comprising a median (range) of 105.0 (45.0–143.0) exposure days (EDs). The median (range) cumulative treatment duration from XTEND-1 baseline was 164.0 (89.3–188.6) weeks with median (range) 157.0 (81–197) EDs. FVIII inhibitors were not detected. The mean (95% confidence interval) model-based ABR for the efficacy period for overall treated bleeds was 0.60 (0.36; 1.00), spontaneous bleeds was 0.13 (0.05; 0.34), and traumatic bleeds was 0.33 (0.15; 0.73); 6-monthly data in Table 1. Of 23 treated bleeding episodes, 20 (87.0%) resolved with 1 injection of efanesoctocog alfa; participants rated the response as excellent/good for 14/15 (93.3%) bleeds. The median (range) total weekly efanesoctocog alfa consumption was 51.9 (41.3–54,3) IU/kg. Overall, 19 (95.0%) participants experienced ≥1 treatment-emergent adverse event (TEAE) and 4 (20.0%) participants experienced ≥1 serious TEAE (TESAE); however, none of the TEAEs or TESAEs were considered related to study treatment. One TEAE led to treatment discontinuation (Table 2). Conclusions: Long-term results with an additional 2 years of treatment in XTEND-ed for the North American XTEND-1 cohort of adults and adolescents show that once-weekly efanesoctocog alfa continues to provide high efficacy and is well tolerated, consistent with the overall population. No inhibitors were detected and ABRs remained low.

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