Annette von Drygalski, MD, PharmD, Associate Clinical Professor of Medicine in the Division of Hematology/Oncology, and Director of the Hemophilia and Thrombosis Treatment Center, Department of Medicine, at the University of California, San Diego, discusses positive results from the XTEND-1 study of efanesoctocog alfa (BIVV001) in previously treated adults and adolescents ≥12 years with severe hemophilia A. These results were recently presented at this year’s International Society on Thrombosis and Haemostasis (ISTH) Congress.

Hemophilia A is a rare bleeding disorder in which the ability of a person’s blood to clot is impaired due to a lack of factor VIII. Hemophilia A occurs mostly in males. People with hemophilia can experience bleeding episodes that can cause pain, irreversible joint damage and life-threatening hemorrhages. Factor replacement therapy remains a cornerstone of care and can be used across multiple treatment scenarios.

As Dr. von Drygalski explains, the XTEND-1 study is a pivotal phase 3 study evaluating the safety, efficacy and pharmacokinetics of efanesoctocog alfa, an investigational factor VIII replacement therapy, in previously treated adults and adolescents ≥12 years with severe hemophilia A. The study met its primary efficacy endpoint, with once-weekly efanesoctocog alfa prophylaxis providing clinically meaningful bleed protection for people with severe hemophilia A. The median and mean annualized bleeding rates (ABR) were 0.00 and 0.71, respectively. The study also met the key secondary endpoint, demonstrating superior bleed protection (P < .0001) over prior factor VIII prophylaxis with an estimated ABR reduction of 77% and a mean ABR of 0.69 compared to 2.96 on prior prophylaxis, based on an intra-patient comparison (n=78). In a subset of participants (n=17) studied at baseline and week 26, mean factor VIII levels remained in the normal to near-normal range (>40 IU/dL) for the majority of the week, and at 15 IU/dL at day seven post-dose, providing increased factor activity level protection for patients with once-weekly prophylaxis.

Additionally, the data show individuals treated with once-weekly efanesoctocog alfa experienced statistically significant and clinically meaningful improvements in physical health (P = .0001), pain intensity (P = .0276), and joint health (P = .0101) when comparing week 52 and baseline measurements. Moreover, efanesoctocog alfa was effective at treating bleeds, including in target joints; 96.7% of bleeds were resolved with a single 50 IU/kg dose. 

Efanesoctocog alfa was well tolerated and inhibitor development to factor VIII was not detected. The most common treatment-emergent adverse events (>5% of participants overall) were headache, arthralgia, fall, and back pain.

As for next steps, all patients in the XTEND-1 study had the option to enroll in an open-label extension study, which is currently ongoing. 

To learn more about hemophilia A and other rare hematological disorders, visit