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Submission is to expand HYMPAVZI indication to the treatment of hemophilia A or B patients 6 years and older with inhibitors, and pediatric patients (ages 6 to 11) without inhibitors
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If approved, HYMPAVZI would become the first non-factor prophylactic treatment available for children aged 6 to 11 years with hemophilia B
February 06, 2026 --NEW YORK--(BUSINESS WIRE)-- Pfizer Inc. (NYSE: PFE)today announced that the U.S. Food and Drug Administration (FDA) has accepted and granted Priority Review for the company’s supplemental Biologics License Application (sBLA) for HYMPAVZI® (marstacimab) to expand the approved indication to include the treatment of hemophilia A or B patients 6 years and older with inhibitors, and pediatric patients (ages 6 to 11) with hemophilia A or B without inhibitors. In the U.S., HYMPAVZI is currently approved for the treatment of patients 12 years of age and older with hemophilia A without factor VIII (FVIII) inhibitors, or hemophilia B without factor IX (FIX) inhibitors.
The FDA has set a Prescription Drug User Fee Act (PDUFA) action date in the second quarter of 2026. If approved, HYMPAVZI would offer a combination of bleed protection with a straightforward, once-weekly subcutaneous injection administration, requiring minimal preparation and no routine treatment-related lab monitoring for these difficult-to-treat patient populations.
“There is a significant medical need for younger patients with hemophilia and for those who have developed inhibitors, which neutralize factor replacement therapies and render them ineffective,” said Michael Vincent, M.D., Ph.D., Chief Inflammation & Immunology Officer, Pfizer. “Based on the findings in the BASIS clinical trial program and if approved, we believe HYMPAVZI has the potential to become a transformative option for these patients that have limited or burdensome treatment options today. We look forward to progressing discussions with regulators to make this medicine available for patients.”
Hemophilia is diagnosed in early childhood and impacts more than 800,000 people worldwide.1 The inability of the blood to clot properly can increase the risk of painful bleeding, including inside the joints, which can cause joint scarring and damage.2,3 Children’s joints have growing cartilage and bone, which makes them particularly susceptible to damage caused by repeated bleeding episodes.4 Inhibitors, or antibodies, develop in approximately 20% of people with hemophilia A and 3% of people with hemophilia B. People living with inhibitors to FVIII and FIX are unable to continue taking factor replacement therapies as they no longer prevent or stop bleeding episodes, particularly in individuals who are refractory to immune tolerance induction therapy.1,5,6
“For children living with hemophilia A or B between ages 6 and 11, treatment approaches that prevent bleeds are particularly important to protect growing joints,” said Guy Young, M.D., Director, Hemostasis and Thrombosis Center at Children's Hospital, Los Angeles. “HYMPAVZI would address a critical unmet medical need for these patients and those with inhibitors if approved, particularly patients ages 6 to 11 with hemophilia B who do not have non-factor treatment options available today.”
The FDA grants Priority Review to medicines that may offer significant advances in treatment or may provide a treatment where no adequate therapy exists. Priority Review designation by the FDA shortens the standard sBLA review period by four months.
The FDA also granted HYMPAVZI Breakthrough Therapy Designation for routine prophylaxis to prevent or reduce the frequency of bleeding episodes in younger pediatric (≥6 to <12 years of age) patients with hemophilia B with and without inhibitors. The FDA’s Breakthrough Therapy Designation is intended to expedite the development and review of medicines with the potential to treat a serious or life-threatening disease, when preliminary clinical evidence indicates the medicine may demonstrate substantial improvement over existing therapies.
The submission for HYMPAVZI in adults and adolescents is based on efficacy and safety data from the inhibitor cohort of the Phase 3 BASIS trial (NCT03938792). The submission for HYMPAVZI in children aged 6 to 11 years with or without inhibitors is supported by efficacy and safety data from the Phase 3 BASIS KIDS trial (NCT05611801).
The use of HYMPAVZI for the treatment of patients 12 years and older living with hemophilia A or B with inhibitors is also under review by the European Medicines Agency.
About HYMPAVZI
Discovered by Pfizer scientists, HYMPAVZI has a unique mechanism of action that is differentiated from FVIII and FIX replacement treatments. Instead of replacing missing or insufficient clotting factors, HYMPAVZI is intentionally designed to target tissue factor pathway inhibitor (TFPI), one of the body’s natural mechanisms that inhibits the initiation of blood clotting. By targeting the Kunitz 2 domain of TFPI, HYMPAVZI may help re-establish balance between bleeding and blood clot formation with the goal of offering a combination of bleed protection and straightforward administration.
HYMPAVZI is a hemophilia treatment that has received regulatory approvals in more than 40 countries for eligible patients living with hemophilia A without factor VIII inhibitors, or hemophilia B without factor IX inhibitors. HYMPAVZI was the first anti-TFPI approved in the U.S. and EU for the treatment of hemophilia A or B and the first hemophilia medicine approved in the U.S. and EU to be administered via a pre-filled, auto-injector pen. For eligible people living with hemophilia B, it is the first once-weekly subcutaneous prophylactic treatment. HYMPAVZI is a subcutaneous treatment option with a once-weekly dosing schedule and minimal preparation required for each individual administration.
About the BASIS Clinical Trial
The pivotal BASIS study is a global, Phase 3, open-label, multicenter study to evaluate the efficacy data and safety profile of HYMPAVZI in adolescent and adult participants ages 12 to <75 years with severe hemophilia A (defined as FVIII <1%) or moderately severe to severe hemophilia B (defined as FIX activity ≤2%) with or without inhibitors. The with inhibitor cohort included 48 people living with hemophilia with inhibitors who were treated with HYMPAVZI during a 12-month active treatment period (ATP) versus an on-demand intravenous regimen with bypassing agents, administered as part of usual care in a six-month observational period. During the ATP, participants received prophylaxis (a 300 mg subcutaneous loading dose of HYMPAVZI, followed by 150 mg subcutaneously once weekly) with potential for dose escalation to 300 mg once weekly. An additional three patients in the inhibitor cohort were on routine prophylactic treatment prior to the study and not included in the primary efficacy analysis. The primary endpoint measures the treated ABR (annualized bleeding rate) during the 12-month ATP with HYMPAVZI compared to treated ABR on prior on-demand bypass therapy. For further information, visit clinicaltrials.gov.
About the BASIS KIDS Clinical Trial
The BASIS KIDS study is a global, Phase 3, open-label study investigating the safety and efficacy of HYMPAVZI in children 1 to <18 years of age with severe hemophilia A or moderately severe to severe hemophilia B with or without inhibitors. There were 68 patients aged 6 to 11 years treated with HYMPAVZI during a 12-month ATP versus routine prophylaxis with factor replacement therapy (without inhibitor), or routine prophylaxis or on-demand treatment with bypassing agents (with inhibitor), administered as part of usual care in a 12-month period prior to enrollment. During the ATP in this age group, participants received prophylaxis (a 150 mg subcutaneous loading dose of HYMPAVZI, followed by 75 mg subcutaneous once weekly) with the potential for dose escalation to 150 mg once weekly. The primary endpoint measures treated ABR during the 12-month ATP with HYMPAVZI compared to ABR on prior routine prophylaxis with factor replacement therapy, or routine prophylaxis or on-demand treatment with bypassing agents. For further information, visit clinicaltrials.gov.
About Hemophilia
Hemophilia is a family of rare genetic blood diseases caused by a clotting factor deficiency (FVIII in hemophilia A, FIX in hemophilia B), which prevents normal blood clotting. Hemophilia is diagnosed in early childhood and impacts more than 800,000 people worldwide.1 The inability of the blood to clot properly can increase the risk of painful bleeding, including inside the joints, which can cause joint scarring and damage. People living with hemophilia can suffer permanent joint damage following repeated bleeding episodes.2,3 Children’s joints have growing cartilage and bone, which makes them particularly susceptible to damage caused by repeated bleeding episodes.4
For decades, the most common treatment approach for hemophilia A and B has been factor replacement therapy, which replaces the missing clotting factors.2,7 Factor replacement therapies increase the amount of clotting factor in the body to levels that improve clotting, resulting in less bleeding.2,3 The burden of intravenous infusions is believed to be a barrier to treatment adherence for some people living with hemophilia due in part to inconvenience, time constraints, and poor venous access.8,9
Approximately 20% of people with hemophilia A and 3% of people with hemophilia B are unable to continue taking factor replacement therapies because they develop inhibitors to FVIII and FIX, respectively.1,6,7 These patients often have higher treatment burden, including potential complications from bleeding such as hospitalization and death, as well as higher treatment-related costs.10,11,12
About Pfizer: Breakthroughs That Change Patients’ Lives
At Pfizer, we apply science and our global resources to bring therapies to people that extend and significantly improve their lives. We strive to set the standard for quality, safety and value in the discovery, development and manufacture of health care products, including innovative medicines and vaccines. Every day, Pfizer colleagues work across developed and emerging markets to advance wellness, prevention, treatments and cures that challenge the most feared diseases of our time. Consistent with our responsibility as one of the world's premier innovative biopharmaceutical companies, we collaborate with health care providers, governments and local communities to support and expand access to reliable, affordable health care around the world. For 175 years, we have worked to make a difference for all who rely on us.
References
1 World Federation of Hemophilia. World Federation of Hemophilia Global Report on the Annual Global Survey 2024. https://www1.wfh.org/publications/files/pdf-2588.pdf.
2 Srivastava A, Santagostino E, Dougall A, et al. WFH guidelines for the management of hemophilia, 3rd Edition. Haemophilia. 2020;26 Suppl 6:1–158. doi:10.1111/hae.14046
3 Franchini M, Mannucci PM. Past, present and future of hemophilia: A narrative review. Orphanet J Rare Dis. 2012;7:24. doi:10.1186/1750-1172-7-24
4 Gualtierotti R, Solimeno LP, Peyvandi F. Hemophilic arthropathy: current knowledge and future perspectives. J Thromb Haemost. 2021;19(9):2112–2121. doi:10.1111/jth.15444
5 Teiu P, Chan A, Matino D. Molecular Mechanisms of Inhibitor Development in Hemophilia. Mediterr J Hematol Infect Dis. 2020 Jan 1;12(1):e2020001. doi:10.4084/MJHID.2020.001
6 Centers of Disease Control and Prevention. Testing for Inhibitors and Hemophilia. Accessed February 2026. Available at: https://www.cdc.gov/hemophilia/testing/testing-for-inhibitors-and-hemophilia.html?.
7 Weyand AC, Pipe SW. New therapies for hemophilia. Blood. 2019;133(5):389–398. doi:10.1182/blood-2018-08-872291
8 Valentino LA, Ewenstein B, Navickis RJ, Wilkes MM. Central venous access devices in haemophilia. Haemophilia. 2004;10(2):134-46. doi:10.1046/j.1365-2516.2003.00840.x
9 Nugent D, Kalnins W, Querol F, et al. Haemophilia Experiences, Results and Opportunities (HERO) study: Treatment-related characteristics of the population. Haemophilia. 2015;21(1):e26-38. doi:10.1111/hae.12545
10 Oladapo AO, Lu M, Walsh S, O’Hara J, Kauf TL. Inhibitor clinical burden of disease: a comparative analysis of the CHESS data. Orphanet Journal of Rare Diseases. 2018;13:198. doi:10.1186/s13023-018-0929-9
11 Soucie JM, Symons Jt, Evatt B, Brettler D, Huszti H, Linden J. Home-based factor infusion therapy and hospitalization for bleeding complications among males with haemophilia. Haemophilia. 2001;7(2):198-206. doi:10.1046/j.1365-2516.2001.00484.x
12 Walsh CE, Soucie JM, Miller CH. Impact of inhibitors on hemophilia a mortality in the United States. Am J Hematol. 2015;90:400–405. doi:10.1002/ajh.23957