ClinicalTrials.gg
Sign In
RecruitingNCT05611801BASIS KIDSUpdated Oct 14, 2026

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

A Phase 3 interventional study of marstacimab in Hemophilia A and Hemophilia B, sponsored by Pfizer. Recruiting at 63 sites in 23 countries. Open to male participants aged 1 Year to 17 Years. Per ClinicalTrials.gov, last updated 2026-10-14.

Sponsored by Pfizer · Phase 3, Interventional, and Treatment

From the registry’s dates

  • Started Dec 2022; still recruiting 3 years 11 months later.
Updated Oct 14, 2026Site recruiting status changedEligibility revised+3 moreGo to Updates ↓
Phase
Phase 3
Study type
Interventional
Enrollment
100
Allocation
Not applicable
Ages
1 Year to 17 Years
Sex
Male
01

Study summary

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 opened the enrollment to adolescent participants aged 12 to 17 years first. Then children aged 6 to 11 years erere permitted to enroll. Lastly, children aged 1 to 5 years are permitted to enroll.

This study will enroll male 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 for participants from 6 to 17 years of age, and at least 3 months prior to entering the study for participants from 1 to 5 years of age
  • 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 for participants from 6 to 17 years of age, and least 3 months for participants aged from 1 to 5 years of age
  • if an inhibitor patient, must be on an on-demand bypass treatment regimen during the 12 months prior to study entry for participants from 6 to 17 years of age, and during the 3 months prior to study entry for participants aged from 1 to 5 years of age

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.

02

Conditions studied

  • Hemophilia A
  • Hemophilia B

Keywords

  • Factor VIII Inhibitor
  • Factor IX Inhibitor
  • PF-06741086
  • Marstacimab
  • Anti-TFPI
  • Factor VIII
  • Factor IX
  • Inhibitors
  • Anti-Tissue Factor Pathway Inhibitor (TFPI)
  • Subcutaneous (sc)
  • Prophylaxis
  • On-Demand
  • BASIS KIDS
  • Inhibitor
  • SC
  • Subcutaneous
  • Injection
  • On demand
  • aTFPI
  • Severe hemophilia
  • Severe bleeding
  • Hemophilia
03

In context

Hemophilia A

844 studies on the registry are indexed under Hemophilia A; 138 are open to participants now.

This study's planned enrollment of 100 is above the median of 30 across 499 interventional studies indexed under Hemophilia A.

Browse Hemophilia A studies →

Lead sponsor

Pfizer is the lead sponsor of 3,334 studies on the registry; 149 are open to participants now.

Of its 601 completed or terminated interventional studies of FDA-regulated products, 391 (65%) have results posted.

Browse Pfizer studies →

Counted across the registry records on this site, refreshed daily.

04

Who can participate

The criteria were revised on the registry on Oct 14, 2026. See what changed

Ages eligible
1 Year to 17 Years
Sexes eligible
Male
Accepts healthy volunteers
No

Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.

Inclusion criteria

  • Male participants of appropriate age and required minimum weight
  • Participants aged 12 to 17 years must be at least 25 kgs at time of consent.
  • Participants aged 6 to 11 years must be at least 19 kgs at time of consent.
  • Participants aged 1 to 5 years must be at least 5 kgs at time of consent.
  • Participants with a diagnosis of severe hemophilia A or moderately severe to severe hemophilia B
  • Participants must have at least 1 year (if aged 6 to 17 years), or at least 3 months (if aged 1 to 5 years) of diary and/or medical records available in which exogenous FVIII or FIX replacement or bypass agent infusions and hemophilic bleeding episodes were consistently documented over over the above specified timeframe to the time of consent.

Participants who are enrolled into the Non-Inhibitor Cohort must also meet the following criteria:

  • No current detectable inhibitor and no documented history of inhibitors in the 5 years prior to consent
  • Must have at least 50 exposure days to FVIII/FIX replacement products for participants aged 6 to 17 years. Participants from 1 to 5 years do not require a minimum documented number of exposure days
  • Must be at least 80% compliant with a stable and effective routine prophylaxis regimen with FVIII/FIX replacement products, for at least 12 months prior to consent for participants aged 6 to 17 years, for at least 3 months prior to consent for participants from 1 to 5 years

Participants who are enrolled into the Inhibitor Cohort must also meet the following criteria:

  • Documentation of current high titer inhibitor (≥5 BU/mL); or current low titer inhibitor (\<5 BU/mL) to FVIII or FIX replacement and with FVIII or FIX recovery \<60% of expected within previous 12 months prior to the time of consent
  • Participants who have documented inhibitors while on factor-replacement therapy but who do not meet the high quantitative inhibitor criteria described in the prior bullet at the time of screening (eg, participant with a previously documented high-titer inhibitor ≥5 BU/mL) and whose condition precludes re-challenge with FVIII or FIX replacement may be considered for eligibility on a case-by-case basis with discussion and agreement from the Pfizer medical monitor.
  • Participants aged 6 to 17 years: Hemophilia A participants with on-demand treatment regimen with ≥12 bleeding episodes or hemophilia B participants with on-demand treatment regimen with ≥8 bleeding episodes (spontaneous or traumatic) necessitating treatment with bypass factor in the 12 months prior to
  • Participants aged 1 to 5 years of age with at least 3 months' on-demand bypass treatment regimen and at least 1 treated hemophilic bleeding in the last 3 months or at least 2 treated hemophilic bleedings in the last 6 months documented prior to the time of informed consent
  • Participants aged 6 to 17 years must be on an on-demand bypass treatment regimen during the 12 months prior to informed consent
  • Participants aged 1 to 5 years of age must be on an on-demand bypass treatment regimen during the 3 months prior to informed consent

Exclusion criteria

Exclusion Criteria:

  • Known coronary artery, thrombotic, or ischemic disease, or current evidence of congenital or acquired thrombophilic disease such as Anti-thrombin III deficiency, Factor V Leiden mutation, prothrombin 20210 mutation, protein C deficiency, protein S deficiency and antiphospholipid syndrome.
  • Known planned surgical procedure during the planned study period
  • Known hemostatic defect other than hemophilia A or B
  • Abnormal hematology, renal or hepatic function laboratory results at screening
  • Current unstable liver or biliary disease per investigator assessment defined by the presence of ascites, encephalopathy, coagulopathy, hypoalbuminaemia, oesophageal or gastric varices, persistent jaundice, or cirrhosis. Participants aged 1 to 5 years with known or C will also be excluded
  • Known -positive for participants aged 1 to 5 years of age
  • Other acute or chronic medical or psychiatric condition that may increase the risk associated with study participation or product administration or may interfere with the interpretation of study results and, in the judgment of the investigator
  • Individuals with known allergic reaction or to hamster protein or other components of the study intervention
  • Current routine prophylaxis with bypassing agent, non-coagulation non-factor replacement therapy (eg, emicizumab), or any previous treatment with a gene therapy product for treatment of hemophilia
  • Participants with inhibitors who are being treated using a prophylaxis treatment regimen with a bypass agent, and, participants who have previously received non-factor-based hemophilia therapy (eg, fitusiran, concizumab, emicizumab) will be considered on a case-by-case basis, only after discussion and agreement between the investigator and the Pfizer medical monitor
  • Regular use of immunomodulatory medications (eg, IVIG, routine systemic , rituximab)
  • Use of systemic antifibrinolytics, medications that may increase the risk of bleeding, and certain non-steroidal anti-inflammatory drugs within 120 hours of first dose of study intervention and while on study. Some of these agents may be permitted if it is authorized for use in the respective country, is part of the standard of care in the study population, its use is short term and on a PRN basis and following discussion with the Pfizer medical monitor.
  • Ongoing or planned use of ITI, or prophylaxis with FVIII or FIX replacement at any time after initiation of treatment with study intervention
  • Participation in other studies involving investigational drug(s) or investigational vaccine(s) within 30 days (or as determined by local requirements) or 5 half-lives prior to study entry or during study participation
  • Previous exposure to marstacimab during participation in other marstacimab clinical studies
  • ≤200/uL if HIV-positive, for participants aged 6 to 17 years
  • Abnormal of clinical relevance that may affect participant safety or interpretation of study results
  • Investigator site staff members directly involved in the conduct of the study and their family members, site staff members otherwise supervised by the investigator, and sponsor and sponsor delegate employees directly involved in the conduct of the study and their family members
Terms in these criteria, in plain language(9)

Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.

Relapsed and refractory

Relapsed: the illness came back after treatment had worked. Refractory: it did not respond to treatment, or stopped responding while still on it.

Informed consent

Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.

You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.

Hepatitis B tests

Hepatitis B is a virus that infects the liver. These are separate tests: HBsAg positive usually means a current infection (a recent vaccination can briefly cause it too); total anti-HBc (HBcAb) positive means an infection now or in the past; HBV DNA measures how much virus is in the blood.

Some studies accept a past infection if HBV DNA is undetectable, sometimes with antiviral medicine during the study. Check what this study allows.

HIV

The human immunodeficiency virus, which weakens the immune system.

Many studies now accept people whose HIV is controlled on treatment, judged by the viral load and the CD4 count. Check the limits this study sets.

Investigational drug or device

A drug or device being studied in a clinical trial.

It may be new, or already approved and being studied for another use, dose or form. Criteria often leave out people who took part in another study of one within a recent period, commonly 30 days or five half-lives.

Hypersensitivity

An allergy, or another reaction of the immune system, to a substance. “Hypersensitivity to the study drug” means a known allergic reaction to it — not every side effect a medicine can have.

Corticosteroids (steroids)

Anti-inflammatory medicines such as prednisone, prednisolone and dexamethasone — not the anabolic steroids used for muscle.

Studies differ in what they allow: check which steroid medicines, routes (tablets, injections, creams, inhalers, eye drops) and doses this study accepts.

CD4 count

The number of CD4 cells, a type of white blood cell, in a given amount of blood. It is used to follow how well the immune system is doing in HIV.

ECG (electrocardiogram)

A recording of the heart’s electrical activity, taken with stickers on the chest, arms and legs. It takes a few minutes and does not hurt.

05

Study design

Phase
Phase 3
Primary purpose
Treatment
Allocation
Not applicable
Intervention model
Single group
Masking
None (open label)
Enrollment
100 participants (estimated)

Study arms

  • Experimental
    marstacimab (PF-06741086)

    Weekly subcutaneous injections.

    Drug: marstacimab

Interventions

06

What researchers measure

Primary outcomes

  1. Annualized bleeding rate (ABR) of treated bleeding events

    Derived for each subject for each period (historical and study treatment) by using the following formula: ABR = number of bleeds requiring treatments/ (days on treatment period / 365.25)

    Time frame: Baseline (up to 12 months prior to informed consent) to the end of the 12-month treatment period

  2. Incidence of adverse events and serious adverse events

    Time frame: Screening through end of follow-up period (approximately 14 months)

  3. Incidence and severity of thrombotic events

    Time frame: Baseline to end of 12-month treatment period

  4. Incidence and severity of thrombotic microangiopathy

    Time frame: Baseline to end of 12-month treatment period

  5. Incidence and severity of disseminated intravascular coagulation/consumption coagulopathy events

    Time frame: Baseline to end of 12-month treatment period

  6. Immunogenicity (incidence of ADA and clinically significant persistent NAb against marstacimab)

    Time frame: Baseline to end of 12-month treatment period

  7. Incidence and severity of injection site reaction

    Time frame: Baseline to end of 12-month treatment period

  8. Incidence of severe hypersensitivity and anaphylactic reactions

    Time frame: Baseline to end of 12-month treatment period

Secondary outcomes

  1. Incidence of joint bleeds (treated)

    Time frame: Baseline to end of 12-month treatment period

  2. Incidence of spontaneous bleeds (treated)

    Time frame: Baseline to end of 12-month treatment period

  3. Incidence of target joint bleeds (treated)

    Time frame: Baseline to end of 12-month treatment period

  4. Incidence of total bleeds (treated and untreated)

    Time frame: Baseline to end of 12-month treatment period

  5. Number of target joints

    Time frame: Baseline to end of 12-month treatment period

  6. Change from baseline in joint health as measured by the HJHS for participants ≥4 years of age

    Time frame: Baseline to end of 12-month treatment period

  7. Changes in quality of life measured by Haem-A-QoL/Haemo-QoL (using age-dependent versions for participants ≥8 years of age)

    Time frame: Baseline to end of 12-month treatment period

  8. Changes in quality of life measured by pedHAL (using age-dependent versions for participants ≥4 years of age)

    Time frame: Baseline to end of 12-month treatment period

  9. Changes in quality of life measured by Patient Global Impression of Change - Hemophilia for participants ≥4 years of age

    Time frame: Baseline to end of 12-month treatment period

  10. Changes in quality of life measured by Health Utilities Measure (EQ-5D-Y) for participants ≥4 years of age

    Time frame: Baseline to end of 12-month treatment period

07

Study locations

51 of 63 sites recruiting
08

References and documents

Individual participant data

Plan to share: Yes — Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical_trials/trial_data_and_results/data_requests.

Data sharing details ↗ · www.pfizer.com

09

Timeline

1 registry update since Sep 25, 2026
ElapsedEstimatedEstimated, not yet reachedSimilar studies: half by the dot; the band is the middle halfHalf of similar studies reached it by the dot; the band is the middle half, from a quarter to three quarters

Started Dec 2022 (actual). Primary completion is estimated for Sep 2028, 69 months after the start.

Of 89 industry-sponsored phase 3 interventional studies under Hemophilia A, half reached primary completion within 32 months of starting (the median), counting those still running; a quarter within 18 and three quarters within 56. This study's planned 69 months is above that.

Counting every sponsor, half of 91 studies reached it within 33 months; a quarter within 20 and three quarters within 56.

How these figures are worked out, and which studies are left out of them.

Registered
Oct 27, 2022
First posted
Nov 10, 2022
StartActual
Dec 9, 2022
Primary completionEst.
Sep 10, 2028
CompletionEst.
Sep 10, 2028
Last update
Oct 14, 2026
What these dates mean
Start.
When the first participant enrolled; while estimated, when the study expects to open to recruitment.
Primary completion.
When the last participant was examined or treated to collect data for the study's main question, its primary outcome. A study that stopped early gives the date its data collection stopped.
Completion.
When the last participant's last visit took place, for every outcome, secondary ones and side effects included: the end of the study. Often later than primary completion, sometimes the same day.
Actual and Est.
Actual means the registry says the date has happened. Est. (estimated) is a date the sponsor plans or expects. It can still move, and the sponsor is expected to change it to actual once it has passed.
Sites
17 sites added, 17 sites removed. 2 sites changed recruiting status (1 now active, not recruiting, 1 now terminated)
Show 2 sites
  • The Affiliated Hospital of Guizhou Medical University · Guiyang, ChinaRecruiting→Active, not recruiting
  • Royal Manchester Children's Hospital · Manchester, United KingdomRecruiting→Terminated
Show 17 added (7 Turkey (Türkiye), 2 Italy, 1 Argentina, 1 Brazil, 1 Denmark, 1 Germany, 1 Japan, 1 Mexico, 1 Saudi Arabia, 1 Spain)
  • Arbesu Hematología · Mendoza, Argentina
  • Centro Estadual de Hemoterapia e Hematologia Marcos Daniel Santos - HEMOES · Maruípe, Brazil
  • Aarhus University · Aarhus N, Denmark
  • Charité Campus Virchow-Klinikum · Berlin, Germany
  • Azienda Ospedaliero Universitaria di Parma · Parma, Italy
  • Azienda Ospedaliero-Universitaria Città della Salute e della Scienza di Torino · Torino, Italy
  • Saga University Hospital · Saga, Japan
  • Arké SMO S.A de C.V · Veracruz, Mexico
  • King Fahad Specialist Hospital · Dammam, Saudi Arabia
  • Hospital Universitario Miguel Servet · Zaragoza, Spain
  • Adana Acibadem Hastanesi Pediatrik Hematoloji Bilim Dali · Adana, Turkey (Türkiye)
  • Gazi University Medical Faculty · Ankara, Turkey (Türkiye)
  • Gazi Universitesi Tip Fakultesi Hastanesi Cocuk Hematologi Bolumu · Ankara, Turkey (Türkiye)
  • Istanbul Universitesi Istanbul Tıp Fakultesi Hastanesi · Istanbul, Turkey (Türkiye)
  • Ege Universitesi Tip Fakultesi Hastanes · Izmir, Turkey (Türkiye)
  • Erciyes University Faculty of Medicine Pediatric · Kayseri, Turkey (Türkiye)
  • Ondokuz Mayıs Universitesi · Samsun, Turkey (Türkiye)
Show 17 removed
  • Arbesu Hematología · Mendoza, Argentina
  • Centro Estadual de Hemoterapia e Hematologia Marcos Daniel Santos - HEMOES · Maruípe, Brazil
  • Aarhus University · Aarhus N, Denmark
  • Charité Campus Virchow-Klinikum · Berlin, Germany
  • Azienda Ospedaliero Universitaria di Parma · Parma, Italy
  • Azienda Ospedaliero-Universitaria Città della Salute e della Scienza di Torino · Torino, Italy
  • Saga University Hospital · Saga, Japan
  • Arké SMO S.A de C.V · Veracruz, Mexico
  • King Fahad Specialist Hospital · Dammam, Saudi Arabia
  • Hospital Universitario Miguel Servet · Zaragoza, Spain
  • Istanbul Universitesi Istanbul Tıp Fakultesi Hastanesi · Istanbul, Turkey (Türkiye)
  • Adana Acibadem Hastanesi Pediatrik Hematoloji Bilim Dali · Adana, Turkey (Türkiye)
  • Gazi University Medical Faculty · Ankara, Turkey (Türkiye)
  • Gazi Universitesi Tip Fakultesi Hastanesi Cocuk Hematologi Bolumu · Ankara, Turkey (Türkiye)
  • Ege Universitesi Tip Fakultesi Hastanes · Izmir, Turkey (Türkiye)
  • Erciyes University Faculty of Medicine Pediatric · Kayseri, Turkey (Türkiye)
  • Ondokuz Mayıs Universitesi · Samsun, Turkey (Türkiye)
Oct 14, 2026
Eligibility
6 inclusion criteria edited, 2 added; 2 exclusion criteria edited, 2 added
What changed in the criteria
Inclusion criteria
  • EditedMinimum weight requirement for participantsParticipants aged 1 to 5 years is tomust be determinedat least 5 kgs at time of consent.
  • EditedParticipants must have at least 1 year (if aged 6 to 17 years), or at least 3 months (if aged 1 to 5 years) of diary and/or medical records available in which exogenous FVIII or FIX replacement or bypass agent infusions and hemophilic bleeding episodes were consistently documented over over the 12 months priorabove specified timeframe to the time of consent.
  • EditedMust have at least 50 exposure days to FVIII/FIX replacement products for participants aged 6 to 17 years. Participants from 1 to 5 years do not require a minimum documented number of exposure days
  • EditedMust be at least 80% compliant with a stable and effective routine prophylaxis regimen with FVIII/FIX replacement products, for at least 12 months prior to consent for participants aged 6 to 17 years, for at least 3 months prior to consent for participants from 1 to 5 years
  • EditedParticipants aged 6 to 17 years: Hemophilia A participants with on-demand treatment regimen with ≥12 bleeding episodes or hemophilia B participants with on-demand treatment regimen with ≥8 bleeding episodes (spontaneous or traumatic) necessitating treatment with bypass factor in the 12 months prior to informed consent
  • AddedParticipants aged 1 to 5 years of age with at least 3 months' on-demand bypass treatment regimen and at least 1 treated hemophilic bleeding in the last 3 months or at least 2 treated hemophilic bleedings in the last 6 months documented prior to the time of informed consent
  • EditedParticipants aged 6 to 17 years must be on an on-demand bypass treatment regimen during the 12 months prior to informed consent
  • AddedParticipants aged 1 to 5 years of age must be on an on-demand bypass treatment regimen during the 3 months prior to informed consent
Exclusion criteria
  • AddedCurrent unstable liver or biliary disease per investigator assessment defined by the presence of ascites, encephalopathy, coagulopathy, hypoalbuminaemia, oesophageal or gastric varices, persistent jaundice, or cirrhosis. Participants aged 1 to 5 years with known hepatitis B or C will also be excluded
  • AddedKnown HIV-positive for participants aged 1 to 5 years of age
  • EditedUse of systemic antifibrinolytics, medications that may increase the risk of bleeding, and certain non-steroidal anti-inflammatory drugs within 120 hours of first dose of study intervention and while on study. Some of these agents may be permitted if it is authorized for use in the respective country, is part of the standard of care in the study population, its use is short term and on a PRN basis and following discussion with the Pfizer medical monitor.
  • EditedCD4 cell count ≤200/uL if HIV-positive, for participants aged 6 to 17 years
Oct 14, 2026
Primary outcomes
1 time frame changed
What changed in the outcomes
  • Time frameAnnualized bleeding rate (ABR) of treated bleeding eventsBaseline to end of 12-month treatment period → Baseline (up to 12 months prior to informed consent) to the end of the 12-month treatment period
Oct 14, 2026
Show all 1 update
  1. Oct 14, 2026
    17 sites added, 17 sites removed. 2 sites changed recruiting status (1 now active, not recruiting, 1 now terminated)
    Show 2 sites
    • The Affiliated Hospital of Guizhou Medical University · Guiyang, ChinaRecruiting→Active, not recruiting
    • Royal Manchester Children's Hospital · Manchester, United KingdomRecruiting→Terminated
    Show 17 added (7 Turkey (Türkiye), 2 Italy, 1 Argentina, 1 Brazil, 1 Denmark, 1 Germany, 1 Japan, 1 Mexico, 1 Saudi Arabia, 1 Spain)
    • Arbesu Hematología · Mendoza, Argentina
    • Centro Estadual de Hemoterapia e Hematologia Marcos Daniel Santos - HEMOES · Maruípe, Brazil
    • Aarhus University · Aarhus N, Denmark
    • Charité Campus Virchow-Klinikum · Berlin, Germany
    • Azienda Ospedaliero Universitaria di Parma · Parma, Italy
    • Azienda Ospedaliero-Universitaria Città della Salute e della Scienza di Torino · Torino, Italy
    • Saga University Hospital · Saga, Japan
    • Arké SMO S.A de C.V · Veracruz, Mexico
    • King Fahad Specialist Hospital · Dammam, Saudi Arabia
    • Hospital Universitario Miguel Servet · Zaragoza, Spain
    • Adana Acibadem Hastanesi Pediatrik Hematoloji Bilim Dali · Adana, Turkey (Türkiye)
    • Gazi University Medical Faculty · Ankara, Turkey (Türkiye)
    • Gazi Universitesi Tip Fakultesi Hastanesi Cocuk Hematologi Bolumu · Ankara, Turkey (Türkiye)
    • Istanbul Universitesi Istanbul Tıp Fakultesi Hastanesi · Istanbul, Turkey (Türkiye)
    • Ege Universitesi Tip Fakultesi Hastanes · Izmir, Turkey (Türkiye)
    • Erciyes University Faculty of Medicine Pediatric · Kayseri, Turkey (Türkiye)
    • Ondokuz Mayıs Universitesi · Samsun, Turkey (Türkiye)
    Show 17 removed
    • Arbesu Hematología · Mendoza, Argentina
    • Centro Estadual de Hemoterapia e Hematologia Marcos Daniel Santos - HEMOES · Maruípe, Brazil
    • Aarhus University · Aarhus N, Denmark
    • Charité Campus Virchow-Klinikum · Berlin, Germany
    • Azienda Ospedaliero Universitaria di Parma · Parma, Italy
    • Azienda Ospedaliero-Universitaria Città della Salute e della Scienza di Torino · Torino, Italy
    • Saga University Hospital · Saga, Japan
    • Arké SMO S.A de C.V · Veracruz, Mexico
    • King Fahad Specialist Hospital · Dammam, Saudi Arabia
    • Hospital Universitario Miguel Servet · Zaragoza, Spain
    • Istanbul Universitesi Istanbul Tıp Fakultesi Hastanesi · Istanbul, Turkey (Türkiye)
    • Adana Acibadem Hastanesi Pediatrik Hematoloji Bilim Dali · Adana, Turkey (Türkiye)
    • Gazi University Medical Faculty · Ankara, Turkey (Türkiye)
    • Gazi Universitesi Tip Fakultesi Hastanesi Cocuk Hematologi Bolumu · Ankara, Turkey (Türkiye)
    • Ege Universitesi Tip Fakultesi Hastanes · Izmir, Turkey (Türkiye)
    • Erciyes University Faculty of Medicine Pediatric · Kayseri, Turkey (Türkiye)
    • Ondokuz Mayıs Universitesi · Samsun, Turkey (Türkiye)
    Eligibility 6 inclusion criteria edited, 2 added; 2 exclusion criteria edited, 2 added
    What changed in the criteria
    Inclusion criteria
    • EditedMinimum weight requirement for participantsParticipants aged 1 to 5 years is tomust be determinedat least 5 kgs at time of consent.
    • EditedParticipants must have at least 1 year (if aged 6 to 17 years), or at least 3 months (if aged 1 to 5 years) of diary and/or medical records available in which exogenous FVIII or FIX replacement or bypass agent infusions and hemophilic bleeding episodes were consistently documented over over the 12 months priorabove specified timeframe to the time of consent.
    • EditedMust have at least 50 exposure days to FVIII/FIX replacement products for participants aged 6 to 17 years. Participants from 1 to 5 years do not require a minimum documented number of exposure days
    • EditedMust be at least 80% compliant with a stable and effective routine prophylaxis regimen with FVIII/FIX replacement products, for at least 12 months prior to consent for participants aged 6 to 17 years, for at least 3 months prior to consent for participants from 1 to 5 years
    • EditedParticipants aged 6 to 17 years: Hemophilia A participants with on-demand treatment regimen with ≥12 bleeding episodes or hemophilia B participants with on-demand treatment regimen with ≥8 bleeding episodes (spontaneous or traumatic) necessitating treatment with bypass factor in the 12 months prior to informed consent
    • AddedParticipants aged 1 to 5 years of age with at least 3 months' on-demand bypass treatment regimen and at least 1 treated hemophilic bleeding in the last 3 months or at least 2 treated hemophilic bleedings in the last 6 months documented prior to the time of informed consent
    • EditedParticipants aged 6 to 17 years must be on an on-demand bypass treatment regimen during the 12 months prior to informed consent
    • AddedParticipants aged 1 to 5 years of age must be on an on-demand bypass treatment regimen during the 3 months prior to informed consent
    Exclusion criteria
    • AddedCurrent unstable liver or biliary disease per investigator assessment defined by the presence of ascites, encephalopathy, coagulopathy, hypoalbuminaemia, oesophageal or gastric varices, persistent jaundice, or cirrhosis. Participants aged 1 to 5 years with known hepatitis B or C will also be excluded
    • AddedKnown HIV-positive for participants aged 1 to 5 years of age
    • EditedUse of systemic antifibrinolytics, medications that may increase the risk of bleeding, and certain non-steroidal anti-inflammatory drugs within 120 hours of first dose of study intervention and while on study. Some of these agents may be permitted if it is authorized for use in the respective country, is part of the standard of care in the study population, its use is short term and on a PRN basis and following discussion with the Pfizer medical monitor.
    • EditedCD4 cell count ≤200/uL if HIV-positive, for participants aged 6 to 17 years
    Primary outcomes 1 time frame changed
    What changed in the outcomes
    • Time frameAnnualized bleeding rate (ABR) of treated bleeding eventsBaseline to end of 12-month treatment period → Baseline (up to 12 months prior to informed consent) to the end of the 12-month treatment period
    + 2 other changes: verification date and description

From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗

10

Registry details

Key details

Study ID
NCT05611801
Lead sponsor
Pfizer
Responsible party
Sponsor
First posted
Nov 10, 2022
Start date
Dec 9, 2022
Primary completion
Sep 10, 2028 (estimated)
Completion
Sep 10, 2028 (estimated)
Last update
Oct 14, 2026

Study contacts

Pfizer CT.gov Call Center
Contact
ClinicalTrials.gov_Inquiries@pfizer.com
1-800-718-1021
Pfizer CT.gov Call Center
study director · Pfizer

Oversight

Data monitoring committee
Yes
FDA-regulated drug
Yes
FDA-regulated device
No
View the source record on ClinicalTrials.gov ↗

Interested in this study?

Eligibility is decided by the study team. Share this record with your doctor or contact the team directly.

Contact study team

Follow this study

Get an email when the registry record changes — status, dates, results — or when someone posts here.

Sign in to follow

Discussion

Questions and observations about this study, from anyone following it. Not medical advice, and not a channel to the study team — their contact details are on the registry record.

Sign in to join the discussion. Reading takes no account; posting does. You choose a display name, and a pseudonym is the default.

Nothing here yet. If you are running this trial, taking part in it, or weighing whether to, this is the place to say so.

Studies of the drug tested here: Marstacimab

Other studies in this condition

Hemophilia A →

Other studies from this sponsor

Pfizer →

Start the discussion