The experimental factor VIII therapy efanesoctocog alfa was granted Breakthrough Therapy Designation for the treatment of hemophilia A by the US Food and Drug Administration (FDA).

This is the first time a factor VIII therapy has been awarded Breakthrough Therapy Designation by the FDA. The decision was based on results from a phase 3 clinical trial called XTEND-1, which showed that efanesoctocog alfa led to clinically meaningful prevention of bleeds and better prevention of bleeding episodes compared to other prophylactic treatments.

“The Breakthrough Therapy designation highlights efanesoctocog alfa’s potential to transform treatment for people with hemophilia A by providing higher protection for longer duration,” John Reed, MD, PhD, global head of research and development at Sanofi, said in a press release.

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“This potential new class of factor VIII therapy represents how we are boldly advancing science to address unmet needs for the hemophilia community. We are excited to work with regulatory authorities during the filing and review of this innovative therapy.”

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XTEND-1 was an open-label, multicenter study assessing the safety, efficacy, and pharmacokinetics of efanesoctocog alfa in previously treated patients aged 12 years and above with severe hemophilia A.

It included 159 participants who took part in the 2-arm study. The first arm consisted of prophylaxis, where patients received efanesoctocog alfa once a week for 52 weeks. In the second arm, patients received efanesoctocog alfa on-demand for 26 weeks. This was followed by a switch to a prophylactic treatment regimen for 26 weeks.

Topline results from the trial showed that the treatment led to clinically meaningful prevention of bleeds over 52 weeks. The treatment was also well-tolerated with no inhibitors against factor VIII detected. The most common treatment-emergent adverse events were headache, arthralgia, falls, and back pain.

Efanesoctocog alfa is a novel recombinant factor VIII therapy. It is designed to extend protection from bleeding in people with hemophilia A. It uses Fc fusion technology, but a region of von Willebrand factor and XTEN® polypeptides are also added to extend its circulation time.


FDA grants efanesoctocog alfa Breakthrough Therapy designation for hemophilia A. News release. Sanofi; June 1, 2022.

A phase 3, open-label interventional study of an intravenous recombinant coagulation factor VIII Fc-von Willebrand factor-XTEN fusion protein, efanesoctocog alfa (BIVV001), in patients with severe hemophilia A (XTEND-1). November 13, 2019. Updated March 7, 2022. Accessed June 6, 2022.