🏛️ Verified NIH Record • Updated 2026-08-06

A Clinical Trial of Study Medicine (Marstacimab) in Pediatric Patients With Hemophilia A or Hemophilia B (NCT05611801)

AN OPEN-LABEL STUDY IN PEDIATRIC (<18 YEARS OF AGE), SEVERE HEMOPHILIA A PARTICIPANTS (COAGULATION FACTOR ACTIVITY <1%) WITH OR WITHOUT INHIBITORS OR MODERATELY SEVERE TO SEVERE HEMOPHILIA B PARTICIPANTS (COAGULATION FACTOR ACTIVITY ≤2%) WITH OR WITHOUT INHIBITORS COMPARING 12 MONTHS OF HISTORICAL STANDARD TREATMENT TO MARSTACIMAB PROPHYLAXIS

🟢 Recruiting Phase3 💊 Investigational Drug / Biologic Sponsor: Pfizer

🩺 Plain-English Summary (8th-Grade Level)

The purpose of this clinical trial is to learn about the safety and effects of the study medicine (called marstacimab) for the potential treatment of hemophilia in pediatric patients. This study will enroll pediatric participants from ages 1 to 17 years in a sequential manner. The study will open enrollment to adolescent participants aged 12 to 17 years first. Then children aged 6 to 11 years will be permitted to enroll. Lastly, children aged 1 to 5 years will be permitted to enroll. This study will enroll participants who: * have severe Hemophilia A or moderately severe to severe Hemophilia B (with or without inhibitors) * have accurate historical records documenting all factor VIII, factor IX, or bypass agent infusions and hemophilia bleed events for at least 1 year prior to entering the study * if a non-inhibitor patient, must be on a stable routine prophylaxis regimen with factor VIII or factor IX replacement products for at least 12 months prior to study entry * if an inhibitor patient, must be on an on-demand bypass treatment regimen during the 12 months prior to study entry All participants in this study will receive marstacimab to use prophylactically. Marstacimab will be given once a week as a subcutaneous (under the skin) shot. The first dose of marstacimab will be given at the study site by the study site staff. During the 12-month treatment period, weekly doses of marstacimab can be given at home, or if preferred, the doses may be given by the study site staff. To help us determine if the study medicine is safe and effective, we will compare participant experiences when they are taking the study medicine to a historical period when they were not. Researchers want to see if the study medicine works to prevent the bleeding episodes commonly experienced by patients with Hemophilia. Participants will be in this study for about 14 months (approximately 1 month in a Screening period, 12 months receiving treatment, and 1 month in a follow-up period) during which they will visit the study site at least 10 times. If preferred, and if local regulations allow it, 2 of the study visits can be completed at the participant's home instead of at the study site. There will also be 6 scheduled telephone calls approximately every 2 months.

Who can join: Review the eligibility criteria below.

Location: Intermountain - Primary Children's Hospital — Salt Lake City, Utah

Age range: 1 Year to 17 Years

🧪 Interventions in This Study

📋 "Do I Qualify?" — 1-Minute Self Screener

Instant Checklist

Full eligibility criteria are available on the official NIH protocol. View the criteria ↗

📍 All Participating Trial Locations (64 Sites)

Showing the first 25 of 64 sites.

  • Intermountain - Primary Children's Hospital — Salt Lake City, Utah
  • Arbesu Hematología — Mendoza,
  • Murdoch Children's Research Institute — Parkville,
  • Medizinische Universität Wien — Vienna, State of Vienna
  • Centro Estadual de Hemoterapia e Hematologia Marcos Daniel Santos - HEMOES — Maruípe, Vitória
  • Stollery Children's Hospital — Edmonton, Alberta
  • Hamilton Health Sciences - McMaster University/McMaster Children's Hospital — Hamilton, Ontario
  • Beijing Children's hospital, Capital Medical University — Beijing, Beijing Municipality
  • Southern Medical University Nanfang Hospital — Guangzhou, Guangdong
  • The Affiliated Hospital of Guizhou Medical University — Guiyang, Guizhou
  • Tongji Hospital of Tongji Medical College of Huazhong University of Science and Technology — Wuhan, Hubei
  • Tongji Hospital of Tongji Medical College of HUST/Pediatric Hematology Department Pharmacy — Wuhan, Hubei
  • Jiangxi Provincial People's Hospital — Nanchang, Jiangxi
  • Institute of hematology&blood disease hospital — Tianjin, Tianjin Municipality
  • Detska nemocnice FN Brno — Brno, Brno-město
  • Fakultni nemocnice Brno — Brno,
  • Motol University Hospital — Prague,
  • Rigshospitalet — Copenhagen, Capital Region
  • Aarhus Universitetshospital, Skejby — Aarhus N,
  • Aarhus University — Aarhus N,
  • Hôpital Universitaire Necker Enfants Malades — Paris,
  • Charité Campus Virchow-Klinikum — Berlin,
  • Nirmal Hospital Pvt Ltd. — Surat, Gujarat
  • K. J. Somaiya Hospital and Research Centre, Somaiya Ayurvihar Complex — Mumbai, Maharashtra
  • Nil Ratan Sircar Medical College and Hospital — Kolkata, West Bengal

📞 Contact the Study Coordinator

Phone: (800) 718-1021

Email: ClinicalTrials.gov_Inquiries@pfizer.com

Coordinator details come directly from the registered NIH protocol. Confirm the study is still recruiting before traveling.

💰 Cost, Insurance & Patient Rights

  • 100% Free Items: The investigational treatment and protocol-required procedures are supplied at zero cost by the sponsor.
  • Routine Patient Care: Under federal law (ACA § 2709) and many state statutes, routine care costs are covered during participation.
  • Voluntary Participation: You may withdraw at any time without affecting your standard medical care.

More studies in Hemophilia A

Explore by condition: All Hemophilia A clinical trials

💡 How to Participate

  1. Check the checklist above to see if you may qualify.
  2. Contact the study coordinator using the phone/email above.
  3. Ask about the visit schedule, what is covered at no cost, and any travel support.
  4. Confirm with your own doctor before making a decision.
🏛️ View Official NIH Record ↗