Open-Label Extension Study of Marstacimab for Hemophilia A and B
This study is testing the long-term safety and effectiveness of marstacimab (PF-06741086) for people with hemophilia A or B, with or without inhibitors (antibodies that make treatments less effective). You may be eligible if you are male, between 1 and 74 years old, and have successfully completed a previous study (B7841005 or B7841008) without early withdrawal. The study will track side effects, serious side effects, and blood clot events for up to 7 years. The study aims to enroll 245 participants.
- Study design
- This is an open-label extension study, meaning both you and your doctors will know you are receiving marstacimab. It is for participants who completed previous Phase 3 studies.
- What's involved
- You will need to comply with all scheduled visits, the treatment plan, laboratory tests, and other study procedures for up to 7 years.
- Compensation
- Not stated in the trial record.
- Follow-up
- The study will follow participants for up to 7 years to monitor adverse events, serious adverse events, and thrombotic events.
AI-generated from the public study record. Only the study team can confirm whether you're eligible — confirm details with them before making decisions.
NCT05145127
Open-Label Extension Study of Marstacimab in Hemophilia Participants With or Without Inhibitors
Recruiting
PHASE3Ages 1–74InterventionalTreatmentPfizer
~245 participants
Updated 2026-07-01 on ClinicalTrials.gov
What's tested:PF-06741086
At a glance
Recruiting sites
69 of 75 listed sites are recruiting right now
RecruitingSuspended, closed, or not yet open
What they're measuring
Number of subject reporting Adverse Events
Measured over Baseline up to 7 years
+9 more outcomes measured
Conditions
Where it's being run
75 sites across 47 statesTurkey (Türkiye)13
Hong Kong4
Spain4
Serbia3
Gauteng3
Ontario2
Jiangxi2
Maharashtra2
Study leadership
- Pfizer CT.gov Call Center · STUDY_DIRECTOR · Pfizer
Who to contact
Opens a ready-to-send draft in your own email app — review before sending.
Do you actually qualify for this trial?
Add a private profile and we'll compare every criterion below against your situation — and tell you which ones are met, uncertain, or excluding.
Eligibility criteria
Inclusion
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
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
What this trial measures
- Number of subject reporting Adverse EventsBaseline up to 7 years
- Number of subjects reporting Serious Adverse EventsBaseline up to 7 years
- Incidence and severity of thrombotic eventsBaseline up to 7 years
- Incidence and severity of thrombotic microangiopathyBaseline up to 7 years
- Number of subjects reporting Disseminated intravascular coagulalopathy/consumption coagulopathyBaseline up to 7 years
- Incidence of clinically significant persistent NAb against marstacimabBaseline up to 7 years
- Incidence and severity of injection site reactionBaseline up to 7 years
- Clinically significant changes in vital signs from baselineBaseline up to 7 years
- Incidence of clinically significant laboratory value abnormalitiesBaseline up to 7 years
- Incidence of severe hypersensitivity and anaphylactic reactionsBaseline up to 7 years