Recruiting
Phase 3

Marstacimab

Sponsor:

Pfizer

Code:

NCT07923981

Conditions

Hemophilia A or B

Eligibility Criteria

Sex: All

Age: 12 - 70+

Healthy Volunteers: Not accepted

Interventions

marstacimab

Study Details

Brief summary:

This is an open-label, multicenter study evaluating the efficacy and safety of marstacimab prophylaxis in approximately 95 male and female adolescents and adults aged 12 to <75 years with mild to moderate hemophilia A or B without inhibitors who have a severe bleeding phenotype. Eligible participants must have baseline factor VIII or factor IX activity levels >1% to ≤15% and a history of clinically significant bleeding despite prior treatment with either on-demand factor replacement therapy or routine factor prophylaxis.

The study will compare bleeding outcomes and other efficacy measures during a historical 12-month period of prescribed factor replacement therapy prior to study entry with outcomes observed during a 12-month treatment phase in which participants receive marstacimab 150 mg administered subcutaneously once weekly. Participants will be enrolled into 2 cohorts based on their treatment regimen before study entry: a prior on-demand treatment cohort and a prior routine prophylaxis treatment cohort.

Female participants with severe hemophilia A or B without inhibitors may also be enrolled on a case-by-case basis. Data from these participants will contribute to safety assessments, and separate descriptive analyses of efficacy outcomes will be performed for all female participants.

The study will also evaluate the long-term safety and efficacy of marstacimab during a long-term extension (LTE) treatment phase of up to 36 months. Participants who complete the 12-month treatment phase may continue into the LTE phase.

Participants may be in the study for approximately 50 months, including a 12-month treatment phase and a long-term extension phase of up to 36 months.

Conditions

Hemophilia A or B

Study ID

NCT07923981

Start date

Oct 23, 2026

Status verified date

Nov, 2026

Completion date

Jun 16, 2032

Anticipated

Primary completion date

Jul 2, 2029

Anticipated

Eligibility Criteria

Eligibility Criteria

Sex: All

Age: 12 - 70+

Healthy Volunteers: Not accepted

Inclusion Criteria

  • Male or female, 12 to less than 75 years of age and weighing at least 35 kg.
  • Moderate hemophilia A or B (factor VIII or factor IX activity ≥1% to ≤5%), or Mild hemophilia A or B (factor VIII or factor IX activity >5% to ≤15%).
  • Females with severe hemophilia A or B may be eligible on a case-by-case basis following discussion with sponsor.
  • No history of factor VIII or factor IX inhibitors within the 5 years before screening.
  • At least 12 months of medical records and/or bleeding diary data documenting hemophilia-related bleeding episodes and factor VIII or factor IX replacement therapy prior to screening.
  • Participants receiving on-demand factor replacement therapy must have had at least 2 treated bleeding episodes during the 12 months before screening (surgical or procedural bleeds do not count).
  • Participants receiving routine prophylactic factor replacement therapy must have received a stable prophylaxis regimen for at least 12 months with ≥80% compliance and at least 1 treated bleeding episode in the 12 months before screening (excluding surgical or procedural bleeds).

Exclusion Criteria

  • Current evidence of a congenital or acquired thrombophilic disorder, including antithrombin III deficiency, Factor V Leiden mutation, prothrombin G20210A mutation, protein C deficiency, protein S deficiency, or antiphospholipid syndrome.
  • Known coronary artery disease, history of venous or arterial thrombosis, or other clinically significant ischemic disease.
  • Any bleeding disorder other than hemophilia A or hemophilia B.
  • Any medical, psychiatric, or laboratory abnormality that, in the investigator's opinion, could increase risk or interfere with study participation.
  • Current use of bypassing agents, non-factor replacement therapies for hemophilia, or prior hemophilia gene therapy.
  • Regular treatment with immunomodulatory medications.
  • Use of prohibited medications, including systemic antifibrinolytic agents, medications that increase bleeding risk, or certain nonsteroidal anti-inflammatory drugs (NSAIDs), as specified by the protocol.
  • Use of estrogen-containing hormonal therapies (including contraceptives and HRTs) within 30 days before or during the study, or depot medroxyprogesterone acetate within 6 months before or during the study.
  • Receipt of another investigational drug or vaccine within 30 days or 5 half-lives before study treatment (whichever is longer), or planned participation in another investigational study during this study.
  • Significant renal or hepatic impairment or clinically significant laboratory abnormalities at screening.
  • Platelet count <100,000/μL, hemoglobin <10 g/dL (with limited exceptions), fibrinogen below the lower limit of normal, or prolonged prothrombin time.
  • CD4 count ≤200 cells/μL in participants with HIV infection.
  • Clinically significant electrocardiogram abnormalities at screening.
  • Planned surgical procedure during the study period.
  • Known hypersensitivity to hamster protein or any component of the study treatment.
  • Study site personnel, sponsor personnel directly involved in the conduct of the study, or their immediate family members.

Study Design

Enrollment

95 participants

Anticipated

Allocation

Randomized

Intervention Model

Single group

Primary purpose

Treatment

Interventions and Outcome Measures

Arms

experimental: marstacimab (PF-06741086)

All enrolled participants will be assigned to treatment with marstacimab (PF-06741086) administered as once weekly SC injection.

Interventions

marstacimab

  • Participants with mild to moderate hemophilia will receive 150 mg subcutaneous (SC) injection once weekly.
  • Female participants with severe hemophilia will receive 300 mg SC loading dose followed by 150 mg SC once weekly. A dose of 300 mg administered SC once weekly may be prescribed for participants who meet the dose-escalation criteria.

Primary outcome measure

  • Annualized Bleeding Rate (ABR) of Treated Bleeding Events [ Time Frame: Baseline (up to 12 months prior to informed consent) up to end of 12-month treatment phase ]

Central Contacts and Locations

Central contacts

Pfizer CT.gov Call Center

1-800-718-1021ClinicalTrials.gov_Inquiries@pfizer.com

Locations

Southern Specialty Clinic

Recruiting

Flowood, Mississippi, United States, 39232

More Information

Sponsor

Pfizer

Last update posted

Nov 9, 2026

Last verified

Nov, 2026

Keywords

  • Hemophilia A
  • Hemophilia B
  • Mild Hemopilia
  • Moderate Hemophlia
  • Non-severe hemophilia
  • Marstacimab
  • PF-06741086
  • Routine Prophylaxis
  • Bleeding Episodes
  • Annualized Bleeding Rate
  • Subcutaneous Administration
  • Women with Hemophilia
  • Factor VIII Deficiency
  • Factor IX Deficiency
  • Female with Hemophilia
  • non-inhibitor

Trial information was received from ClinicalTrials.gov and was last updated on 2026-11-10. This information was provided to ClinicalTrials.gov by Pfizer on 2026-11-09. Recruitment status is synced daily from ClinicalTrials.gov and may not reflect the sponsor's current status. Confirm during your call.