The half-life of efanesoctocog alfa does not appear to be related to endogenous von Willebrand factor (VWF) antigen levels in the treatment of hemophilia A, according to a new post hoc analysis presented at the 63rd American Society for Hematology Annual Meeting & Exposition.

Efanesoctocog alfa is an investigational recombinant factor VIII (rFVIII) treatment. The results showed no correlation between treatment half-life and VWF levels (R2 =.0007; P =.88).

The analysis also found that the clearance of efanesoctocog alfa was not affected by endogenous VWF (R2 =.0493; P =.19). Endogenous VWF levels were found to be relatively stable over time with screening and predose levels being similar to levels at 336 hours post-dose and at the end of the study.

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“[The half-life and clearance of efanesoctocog alfa being independent of VWF levels is] consistent with previous findings from preclinical data and supports the continued evaluation of efanesoctocog alfa as a VWF-independent rFVIII in ongoing Phase 3 clinical trials in hemophilia A,” the authors said.

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The post hoc analysis was performed on data collected from the phase 1/2a single-dose EXTEN-A study (NCT03205163) and phase 1 repeat-dosing trial (EudraCT No: 2018-001535-51). A total of 40 patients with hemophilia A were included (16 from EXTEN-A and 24 from the multiple-dose trial) although only 37 were included in the pooled analysis.

The age of patients ranged from 19 to 63 years with a median of 39 years. During EXTEN-A, patients received a single intravenous dose of either 25 IU/kg or 65 IU/kg while patients in the repeat-dose study received 4 once-weekly doses of either 50 IU/kg or 65 IU/kg.

Efanesoctocog alfa is a novel fusion protein that is able to maintain higher levels of factor VIII activity by decoupling rFVIII from endogenous VWF. Previous research from the clinical trials found that a single dose of treatment could provide sustained factor VIII levels greater than 40% for 3 to 4 days after injection and also keep levels at 10% by the seventh day after treatment.


Staber JM, Lissitchkov T, Konkle BA, et al. Efanesoctocog alfa half-life and clearance are independent of von Willebrand factor in severe hemophilia A: a post-hoc analysis from phase 1/2a studies. Poster presented at: 63rd American Society for Hematology Annual Meeting & Exposition: December 11, 2021; Atlanta, Georgia.