Severe Hemophilia APhase 1NCT06703606
A Study to Learn About How Changing Therapy From Emicizumab to Marstacimab Affects People With the Severe Hemophilia A.
A Phase 1 study testing MARSTACIMAB in people with Severe Hemophilia A, run by Pfizer at 10 sites in 3 countries.
Trial summary
The purpose of the study is to learn about safety, how the body processes marstacimab and how it works in patients with severe hemophilia A without inhibitors. Hemophilia A is rare bleeding disorder where the blood doesn't clot normally. This causes a person to bleed a lot, even from a small cut. Read more about this study
- Who is it for?
- Ages 12 to 74 years, men only
- Conditions the study is for
- Severe Hemophilia A
- What is being tested?
- MARSTACIMAB
- Type of treatment
- Injection or infusion
- Could I receive a placebo?
- No, everyone receives an active treatment
- How many people
- 15 participants
- Where
- 10 sitesin 3 countries
- Study dates
- 13 May 2025to 5 May 2027
- Phase
- Phase 1
- Are there results?
- Not yet: the study is under way
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 12 to 74 years
- Men only
- No healthy volunteers
- Child, Adult, Older adult
Who may be able to join
- Male and 12 to <75 years of age with a minimum body weight of 35 kg at the time of signing the informed consent.
- Diagnosis of severe hemophilia A (FVIII activity <1%) without inhibitors.
- On emicizumab therapy at a standard clinical dose for ≥6 months.
Who cannot join
- Previous or current treatment for or history of coronary artery diseases, venous or arterial thrombosis, or ischemic disease.
- Any medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study.
- Known hemostatic defect other than hemophilia A.
- Current use of any prohibited concomitant medication(s) or unwillingness or inability to use a required concomitant medication(s).
- Previous administration of an investigational product (drug or vaccine) within 30 days or 5 half-lives preceding the first dose of study intervention used in this study (whichever is longer). Participation in studies of other investigational products (drug or vaccine) at any time during participation in this study.
- Platelet count <100,000/μl or hemoglobin <10 g/dL.
Show all 12Show fewer
- Clinically significant renal or hepatic function abnormality based on laboratory results at screening, or known kidney or liver disease.
- CD4 cell count ≤200/μl if HIV positive.
- Screening 12-lead ECG that demonstrates clinically significant abnormalities that, in the opinion of the investigator, may affect participant safety or interpretation of study results.
- Known planned surgical procedure.
- Hypersensitivity or allergic reaction to hamster protein or other components of the study intervention.
- Investigator site staff directly involved in the conduct of the study and their family members, site staff otherwise supervised by the investigator, and sponsor and sponsor-delegate employees directly involved in the conduct of the study and their family members.
Trial locations and contacts
10 sites in 3 countries. Contact the study team or a site near you to ask about taking part.
10 sites in 3 countries
United States6 sites, 6 recruiting
- Recruiting
Brody School of Medicine at East Carolina University
Greenville, North Carolina, 27834
- Recruiting
ECU Health Medical Center
Greenville, North Carolina, 27834
- Not yet recruiting
Altman Clinical and Translational Research Institute-IDS
La Jolla, California, 92037
- Not yet recruiting
Altman Clinical and Translational Research Institute
La Jolla, California, 92037
- Recruiting
Orthopaedic Institute for Children/Orthopaedic Hemophilia Treatment Center
Los Angeles, California, 90007
- Not yet recruiting
UCSD Center for Bleeding and Clotting Disorders
San Diego, California, 92121
India2 sites, 2 recruiting
- Recruiting
K J Somaiya Hospital & Research Centre
Mumbai, Maharashtra, 400022
- Recruiting
Nirmal Hospital Pvt Ltd.
Surat, Gujarat, 395002
Turkey (Türkiye)2 sites, 2 recruiting
- Recruiting
Ege University Faculty of Medicine Dean's Office
Bornova, İzmir, 35100
- Recruiting
Istanbul Universitesi Tıp Fakultesi Onkoloji Enstitusu
Fatih, İ̇stanbul, 34093
About this study
Official title: A PHASE 1B OPEN-LABEL NON-RANDOMIZED STUDY TO ASSESS THE SAFETY, PHARMACOKINETICS, AND PHARMACODYNAMICS OF MARSTACIMAB TREATMENT FOLLOWING THE DISCONTINUATION OF EMICIZUMAB THERAPY IN ADOLESCENT AND ADULT PARTICIPANTS WITH SEVERE HEMOPHILIA A WITHOUT INHIBITORS.
The purpose of the study is to learn about safety, how the body processes marstacimab and how it works in patients with severe hemophilia A without inhibitors. Hemophilia A is rare bleeding disorder where the blood doesn't clot normally. This causes a person to bleed a lot, even from a small cut.
These patients who are on emicizumab medicine for routine prophylaxis for at least 6 months, and desire to switch to marstacimab medicine. Inhibitors are antibodies that the immune system develops because it sees the infused clotting factor as a foreign substance that needs to be destroyed. Antibodies are proteins that eat up the activated factor before it has time to stop the bleeding. Prophylaxis are preventive medicines.
Read more
This study is seeking for participants:
- with severe Hemophilia A withouth inhibitors who are on emicizumab treatment for at least 6 months.
- must be 12 to less than 75 years old
- must have a body weight of at least 35 kilograms. The results from this study will serve as a guide to doctors and their hemophilia A patients who will change their medicines in the real-world clinical setting. Patients who can take part in the study will receive marstacimab medicine as weekly injections under the skin of 150 milligrams for 4 months. Study treatment with marstacimab will be initiated no earlier than 14 days after last dose of emicizumab. The study can last up to 6 months. The sponsor will provide marstacimab. Patients will continue their usual treatment with the infused clotting factor for their bleeds when taking part in the study. Roll-over into an optional study treatment extension period will be available to participants who wish to continue prophylaxis with marstacimab in countries where it is not commercially available.
Read the detailed description
This is a non-randomized open-label study in approximately 10-15 adolescent and adult participants between ages 12 to <75 years with severe hemophilia A (defined as FVIII activity <1%) without inhibitors who are currently on treatment with emicizumab for ≥6 months. The study is designed to assess the safety and PK/PD during a 4-month treatment period with marstacimab 150 mg SC QW after a minimum 14-day wash-out period following discontinuation of emicizumab. Assessment of safety will be conducted by summarizing AEs and SAEs reported during the study, from the time each participant provides informed consent through and including a minimum of 28 calendar days after last dose of study intervention. Participants will continue to use their standard of care factor replacement for breakthrough bleeds during the course of the study. PK, PD, and ADA measurements will support the clinical safety data. The anticipated study duration for an individual participant is approximately 6 months. After completion of marstacimab treatment period participants will resume their standard of care prophylactic treatment after a 14-day wash-out period following the last dose of marstacimab. Roll-over into an optional study treatment extension period will be available to participants who wish to continue prophylaxis with marstacimab in countries where it is not commercially available.
- Conditions
- Severe Hemophilia A
- Being tested
- MARSTACIMAB
- Keywords
- Hemophilia A, Severe Hemophilia A, Severe Hemophilia A Without Inhibitors
- Medical subject headings
- Hemophilia A
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
MARSTACIMABDrug
Also called PF-06741086
Marstacimab 150 mg administered subcutaneous (SC) once weekly (QW)
| Study group | Role | What they receive |
|---|---|---|
| MARSTACIMAB | Experimental | Marstacimab 150 mg subcutaneous (SC) once weekly (QW) Receives: Drug: MARSTACIMAB |
What is being measured
The primary outcome is the main question the study is designed to answer.
Incidence of marstacimab-related adverse events (AEs)
Measured: Approximately 178 days: from the time the participant provides informed consent, through and including a minimum of 28 calendar days after last dose of study treatment
Incidence of marstacimab-related serious AEs (SAEs)
Measured: Approximately 178 days: from the time the participant provides informed consent, through and including a minimum of 28 calendar days after last dose of study treatment
Secondary outcomes (10)
Plasma Concentration Versus Time of Marstacimab (Listings)
Measured: Day 1 up to day 135
Maximum Observed Plasma Concentration (Cmax) of Marstacimab
Measured: Day 1 up to day 135
Average Plasma Concentration (Cavg) of Marstacimab
Measured: Day 1 up to day 135
Minimum Observed Plasma Concentration (Cmin)
Measured: Day 1 up to day 135
Change from baseline in tissue factor pathway inhibitor (TFPI).
Measured: Baseline, Day 1 up to day 135
Change from baseline in prothrombin fragment 1+2 (PF 1+2)
Measured: Baseline, Day 1 up to day 135
Change from baseline in D-dimer
Measured: Baseline, Day 1 up to day 135
Change from baseline in TGA (thrombin generation assay).
Measured: Baseline, Day 1 up to day 135
Incidence of Anti-Drug Antibody (ADA)
Measured: Day 1 up to day 135
Incidence of clinically significant persistent neutralizing antibodies (NAb)
Measured: Day 1 up to day 135
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted25 Nov 2024
- Study start13 May 2025
- Primary completion5 May 2027 (estimated)
- Study completion5 May 2027 (estimated)
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for Severe Hemophilia AStudies of the same condition, open and under way.
- More trials run by PfizerThe sponsor's other registered studies.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase 1
- Primary purpose
- Treatment
- Allocation
- Non-randomised
- Intervention model
- Single group
- Masking
- None (open label)
- Enrolment
- 15 participants (estimated)
Sponsor and investigators
- Lead sponsor
- Pfizer
- Sponsor type
- Industry (pharma, biotech, devices)
- Responsible party
- Sponsor
- Investigators
- Pfizer CT.gov Call Center, Study director, Pfizer
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT06703606
- Sponsor's protocol ID
- B7841014
- Other IDs
- NCT06703606
- Status last verified
- Oct 2026
- First submitted
- 21 Nov 2024
- Last updated
- 15 Oct 2026
- Results posted
- No
- Data monitoring committee
- Yes
- FDA-regulated drug
- Yes
- FDA-regulated device
- No
- Individual data sharing
- No: 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.
Study at a glance
From the registry record, last updated by the sponsor on 15 Oct 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- A PHASE 1B OPEN-LABEL NON-RANDOMIZED STUDY TO ASSESS THE SAFETY, PHARMACOKINETICS, AND PHARMACODYNAMICS OF MARSTACIMAB TREATMENT FOLLOWING THE DISCONTINUATION OF EMICIZUMAB THERAPY IN ADOLESCENT AND ADULT PARTICIPANTS WITH SEVERE HEMOPHILIA A WITHOUT INHIBITORS.
- ClinicalTrials.gov ID
- NCT06703606
- Acronym / sponsor ID
- B7841014
- Conditions
- Severe Hemophilia A
- Keywords
- Hemophilia A, Severe Hemophilia A, Severe Hemophilia A Without Inhibitors
- Phase
- Phase 1
- Study type
- Interventional
- Recruitment status
- Recruiting
- Enrolment
- 15 participants (estimated)
- Lead sponsor
- PfizerIndustry (pharma, biotech, devices)
- Study start
- 13 May 2025 (actual)
- Primary completion
- 5 May 2027 (estimated)
- Study completion
- 5 May 2027 (estimated)
- First posted
- 25 Nov 2024 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
The purpose of the study is to learn about safety, how the body processes marstacimab and how it works in patients with severe hemophilia A without inhibitors. Hemophilia A is rare bleeding disorder where the blood doesn't clot normally. This causes a person to bleed a lot, even from a small cut.
These patients who are on emicizumab medicine for routine prophylaxis for at least 6 months, and desire to switch to marstacimab medicine. Inhibitors are antibodies that the immune system develops because it sees the infused clotting factor as a foreign substance that needs to be destroyed. Antibodies are proteins that eat up the activated factor before it has time to stop the bleeding. Prophylaxis are preventive medicines.
This study is seeking for participants:
- with severe Hemophilia A withouth inhibitors who are on emicizumab treatment for at least 6 months.
- must be 12 to less than 75 years old
- must have a body weight of at least 35 kilograms. The results from this study will serve as a guide to doctors and their hemophilia A patients who will change their medicines in the real-world clinical setting. Patients who can take part in the study will receive marstacimab medicine as weekly injections under the skin of 150 milligrams for 4 months. Study treatment with marstacimab will be initiated no earlier than 14 days after last dose of emicizumab. The study can last up to 6 months. The sponsor will provide marstacimab. Patients will continue their usual treatment with the infused clotting factor for their bleeds when taking part in the study. Roll-over into an optional study treatment extension period will be available to participants who wish to continue prophylaxis with marstacimab in countries where it is not commercially available.
Detailed description
This is a non-randomized open-label study in approximately 10-15 adolescent and adult participants between ages 12 to <75 years with severe hemophilia A (defined as FVIII activity <1%) without inhibitors who are currently on treatment with emicizumab for ≥6 months. The study is designed to assess the safety and PK/PD during a 4-month treatment period with marstacimab 150 mg SC QW after a minimum 14-day wash-out period following discontinuation of emicizumab. Assessment of safety will be conducted by summarizing AEs and SAEs reported during the study, from the time each participant provides informed consent through and including a minimum of 28 calendar days after last dose of study intervention. Participants will continue to use their standard of care factor replacement for breakthrough bleeds during the course of the study. PK, PD, and ADA measurements will support the clinical safety data. The anticipated study duration for an individual participant is approximately 6 months. After completion of marstacimab treatment period participants will resume their standard of care prophylactic treatment after a 14-day wash-out period following the last dose of marstacimab. Roll-over into an optional study treatment extension period will be available to participants who wish to continue prophylaxis with marstacimab in countries where it is not commercially available.
Study design
- Primary purpose
- Treatment
- Allocation
- Non-randomised
- Intervention model
- Single group
- Masking
- None (open label)
- Number of arms
- 1
| Arm | Type | Receives |
|---|---|---|
| MARSTACIMAB | Experimental | Drug: MARSTACIMABMarstacimab 150 mg subcutaneous (SC) once weekly (QW) |
Who may qualify
- Ages
- 12 to 74 years
- Sex
- Male only
- Healthy volunteers
- Not accepted
- Age groups
- Child, Adult, Older adult
Key inclusion criteria (3 listed)
- Male and 12 to <75 years of age with a minimum body weight of 35 kg at the time of signing the informed consent.
- Diagnosis of severe hemophilia A (FVIII activity <1%) without inhibitors.
- On emicizumab therapy at a standard clinical dose for ≥6 months.
Key exclusion criteria (12 listed)
- Previous or current treatment for or history of coronary artery diseases, venous or arterial thrombosis, or ischemic disease.
- Any medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study.
- Known hemostatic defect other than hemophilia A.
- Current use of any prohibited concomitant medication(s) or unwillingness or inability to use a required concomitant medication(s).
- Previous administration of an investigational product (drug or vaccine) within 30 days or 5 half-lives preceding the first dose of study intervention used in this study (whichever is longer). Participation in studies of other investigational products (drug or vaccine) at any time during participation in this study.
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| MARSTACIMABAlso: PF-06741086Marstacimab 150 mg administered subcutaneous (SC) once weekly (QW) | Drug | MARSTACIMAB |
Primary outcome
Incidence of marstacimab-related adverse events (AEs)
Time frame: Approximately 178 days: from the time the participant provides informed consent, through and including a minimum of 28 calendar days after last dose of study treatment
Incidence of marstacimab-related serious AEs (SAEs)
Time frame: Approximately 178 days: from the time the participant provides informed consent, through and including a minimum of 28 calendar days after last dose of study treatment
10 secondary outcomes
Plasma Concentration Versus Time of Marstacimab (Listings)
Time frame: Day 1 up to day 135
Maximum Observed Plasma Concentration (Cmax) of Marstacimab
Time frame: Day 1 up to day 135
Average Plasma Concentration (Cavg) of Marstacimab
Time frame: Day 1 up to day 135
Minimum Observed Plasma Concentration (Cmin)
Time frame: Day 1 up to day 135
Change from baseline in tissue factor pathway inhibitor (TFPI).
Time frame: Baseline, Day 1 up to day 135
Change from baseline in prothrombin fragment 1+2 (PF 1+2)
Time frame: Baseline, Day 1 up to day 135
Change from baseline in D-dimer
Time frame: Baseline, Day 1 up to day 135
Change from baseline in TGA (thrombin generation assay).
Time frame: Baseline, Day 1 up to day 135
Incidence of Anti-Drug Antibody (ADA)
Time frame: Day 1 up to day 135
Incidence of clinically significant persistent neutralizing antibodies (NAb)
Time frame: Day 1 up to day 135
Results and safety
This study is still under way. Results are not available in the source record yet.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 15 Oct 2026.
- To obtain contact information for a study center near you, click here.Link provided by the sponsor.
- Individual participant dataSharing planned: No. 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.
Related trials for Severe Hemophilia A
RecruitingPhase 3
Open-Label Extension Study of Marstacimab in Hemophilia Participants With or Without Inhibitors
Hemophilia A, Hemophilia B
Active, not recruitingPhase 4
A Study to Evaluate Overall Health, Physical Activity, and Joint Outcomes in Participants With Severe or Moderate Hemophilia A Without Factor VIII Inhibitors on Emicizumab Prophylaxis
Severe Hemophilia A, Moderate Hemophilia A
Active, not recruitingPhase 3
A Study to Evaluate the Efficacy and Safety of Factor IX Gene Therapy With PF-06838435 in Adult Males With Moderately Severe to Severe Hemophilia B
Hemophilia B
RecruitingPhase 1/2
A Study to Investigate the Safety and Effectiveness of a Coagulation Factor IX Gene Insertion Therapy (REGV131-LNP1265) in Pediatric, Adolescent and Adult Participants With Hemophilia B
Hemophilia B
Not yet recruitingObservational study
Post Approval Phase 4 Study to Learn More About How Safe Octocog Alfa is, and How Well it Works in Patients With Severe Hemophilia A in India
Severe Hemophilia A
Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part.
Pfizer CT.gov Call Center study director
Pfizer
10 sites in 3 countries: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A Phase 1 study testing MARSTACIMAB in people with Severe Hemophilia A, run by Pfizer at 10 sites in 3 countries.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 3 inclusion and 12 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: looking for participants now, as of the sponsor's last update on 15 Oct 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 10 sites in United States, India, Turkey (Türkiye). Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
What does this phase mean?
Phase 1 studies test a treatment in a small group of people for the first time or in a new way, mainly to check safety and find the right dose.
Not every study follows the same path, and some studies (observational studies, device studies) have no phase.
Are results available for this study?
This study is still under way. Results are not available in the source record yet.
How can a doctor refer a patient or contact the research team?
Contact Pfizer CT.gov Call Center (1-800-718-1021, ClinicalTrials.gov_Inquiries@pfizer.com), or a site near the patient. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Incidence of marstacimab-related adverse events (AEs) (time frame: Approximately 178 days: from the time the participant provides informed consent, through and including a minimum of 28 calendar days after last dose of study treatment). The study lists 2 primary outcomes in all. It is what the study was designed to measure, not a finding.
Where can I read the original study information?
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 15 Oct 2026.