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Long-term treatment with marstacimab for hemophilia patients

AN OPEN-LABEL EXTENSION STUDY TO EVALUATE THE LONG-TERM SAFETY, TOLERABILITY, AND EFFICACY OF MARSTACIMAB PROPHYLAXIS IN SEVERE (COAGULATION FACTOR ACTIVITY <1%) HEMOPHILIA A PARTICIPANTS WITH OR WITHOUT INHIBITORS OR MODERATELY SEVERE TO SEVERE HEMOPHILIA B PARTICIPANTS (COAGULATION FACTOR ACTIVITY ≤2%) WITH OR WITHOUT INHIBITORS

PHASE3 · Pfizer · NCT05145127

This study is testing a long-term treatment called marstacimab to see if it can safely help people with severe hemophilia A or B manage their condition better.

Quick facts

PhasePHASE3
Study typeInterventional
Enrollment245 (estimated)
Ages1 Year to 74 Years
SexMale
SponsorPfizer (industry)
Drugs / interventionsrituximab, marstacimab
Locations75 sites (Iowa City, Iowa and 74 other locations)
Trial IDNCT05145127 on ClinicalTrials.gov

What this trial studies

This open-label extension study evaluates the long-term safety, tolerability, and efficacy of marstacimab, a prophylactic treatment, in participants with severe hemophilia A or B, including those with and without inhibitors. Participants must have previously completed parent studies without early termination. The study aims to provide ongoing treatment through subcutaneous injections of marstacimab, assessing its effectiveness over an extended period. The trial includes both adolescent and adult participants, as well as pediatric patients under 18 years of age.

Who should consider this trial

Good fit: Ideal candidates are individuals aged 12 to under 75 years with severe hemophilia A or moderately severe to severe hemophilia B who have completed prior studies without early termination.

Not a fit: Patients with a history of severe cardiovascular issues, unstable hepatic function, or those requiring planned surgical procedures during the study may not benefit from this treatment.

Why it matters

Potential benefit: If successful, this treatment could significantly improve the management of hemophilia, reducing bleeding episodes and enhancing quality of life for patients.

How similar studies have performed: Other studies involving similar prophylactic treatments for hemophilia have shown promising results, indicating potential for success in this approach.

Eligibility criteria

Show full inclusion / exclusion criteria 
Inclusion Criteria:

* All participants will have a minimum body weight as defined by parent studies
* Participants who are willing and able to comply with all scheduled visits, treatment plan, laboratory tests, and other study procedures.
* Participants have successfully completed participation in parent studies, defined as did not require "Early Termination"

Exclusion Criteria:

* Previous or current treatment for or history of coronary artery disease, venous or arterial thrombosis (CTCAE Grade \>3), or ischemic disease (except catheter-associated thrombosis)
* Abnormal renal function as defined by eGFR \<30 mL.min/1.73 m(2)
* Known planned surgical procedure during the planned study period
* Unstable hepatic function as determined by the Investigator clinical assessment and review of the participant's most recent laboratory results, which would make the participant inappropriate for the study
* For participants known to be HIV+, worsening disease status as determined by the Investigator clinical assessment and review of participant's most recent laboratory results, to include recent locally available CD4 count (if available), which would make the participant inappropriate for the study
* Regular, concomitant therapy with immunomodulatory drugs (eg, IVIG, and routine systemic corticosteroids, rituximab)
* Ongoing or planned use of immune tolerance induction or prophylaxis with FVIII or FIX replacement during the study
* Participation in other study involving investigational drug(s) or investigational vaccine(s) within 30 days or 5 half-lives prior to or during study participation, with the exception of participation in parent studies
* Investigator site staff or Pfizer employees directly involved in the conduct of the study, site staff otherwise supervised by the Investigator, and their respective family members

Where this trial is running

Iowa City, Iowa and 74 other locations

+25 more sites — see ClinicalTrials.gov for the full list.

Study contacts

How to participate

  1. Review the eligibility criteria above with your treating physician.
  2. Visit the official trial page on ClinicalTrials.gov for the most current contact information and recruitment status.
  3. Contact the listed study coordinator or principal investigator to request pre-screening. Pre-screening is free and never obligates you to enroll.

View on ClinicalTrials.gov →

Conditions: Hemophilia A, Hemophilia B, Factor VIII Inhibitor, Factor IX Inhibitor, PF-06741086, Marstacimab, Anti-TFPI

Last reviewed 2026-05-15 by the Find a Trial editorial team. Information on this page is for educational purposes and is not medical advice. Always consult qualified healthcare professionals about clinical trial participation.