Skip to content
Clinical Trials – home

Rare diseases

Investigational molecules

Locations

Our offerNewsroom

RecruitingRare disease

Study on Long-Term Safety and Effects of Marstacimab for Patients with Severe Hemophilia A or B, With or Without Inhibitors

Verified siteInvestigationalNo placebo
Clinical Trials Concierge

Prefer not to search? Our Concierge searches the trials for you.

What is this trial about?

A plain-language summary of the goals, design and what participants do

This clinical trial is focused on studying the long-term safety and effectiveness of a treatment called Marstacimab for people with a condition known as hemophilia. Hemophilia is a rare bleeding disorder where blood doesn't clot properly, leading to excessive bleeding. The study includes individuals with severe hemophilia A or moderately severe to severe hemophilia B, with or without inhibitors. Inhibitors are substances that can interfere with the treatment of hemophilia, making it more challenging to manage the condition.

The purpose of this study is to evaluate how safe and tolerable Marstacimab is when used over a long period. Participants will receive the treatment as a solution for injection, either in a pre-filled pen or syringe, which is administered under the skin. The study will monitor participants for any side effects, including reactions at the injection site, changes in vital signs, and any significant changes in laboratory test results. The study will also track the number of bleeding episodes and any changes in joint health over time.

Participants in this study will be observed for several years to gather comprehensive data on the treatment's impact. The study aims to provide valuable insights into the long-term management of hemophilia using Marstacimab, helping to improve the quality of life for those affected by this condition. The study is open-label, meaning both the researchers and participants know what treatment is being administered, and it is an extension of previous studies, allowing for continued observation and data collection.

The research process

The trial runs in 6 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Joining the study

    Upon joining the study, you will be asked to provide written or electronically signed consent. This ensures that you understand the study and agree to participate. If you are underage, your legal guardian will also need to provide consent.

  2. Step 2

    Initial assessment

    An initial assessment will be conducted to confirm your eligibility. This may include reviewing your medical history and conducting some laboratory tests.

  3. Step 3

    Treatment administration

    You will receive the medication marstacimab as a solution for injection. This will be administered subcutaneously, which means it is injected under the skin. The specific dosage and frequency will be determined by the study team based on your individual needs.

  4. Step 4

    Regular follow-up visits

    You will have regular follow-up visits scheduled throughout the study. During these visits, the study team will monitor your health, check for any side effects, and assess the effectiveness of the treatment.

  5. Step 5

    Reporting side effects

    It is important to report any side effects or unusual symptoms you experience during the study. This helps the study team ensure your safety and adjust the treatment if necessary.

  6. Step 6

    Completion of the study

    At the end of the study, a final assessment will be conducted. This will include a review of your overall health and any changes observed during the study period.

Who can join the trial?

7 criteria

  • Participants must have **hemophilia**, which is a condition that affects the blood's ability to clot.
  • Participants must be between **1 to 74 years old**.
  • Participants must be **male**.
  • Participants must have been part of and successfully completed either **Study B7841005** or **Study B7841008** without needing to leave the study early.
  • Participants must have met the **age and weight requirements** in their previous study (either Study B7841005 or Study B7841008).
  • Participants must be willing and able to attend all scheduled visits, follow the treatment plan, and complete all required tests and procedures.
  • Participants or their legal guardians must provide **written consent** to participate in the study. This means they agree to join the study after being fully informed about what it involves.

Who cannot join the trial?

5 criteria

  • Patients who do not have **severe hemophilia A** or **moderately severe to severe hemophilia B** cannot participate. Hemophilia A and B are conditions where the blood does not clot properly.
  • Patients with **Factor VIII (FVIII) activity** of 1% or more cannot participate. FVIII is a protein that helps blood to clot.
  • Patients with **Factor IX (FIX) activity** of more than 2% cannot participate. FIX is another protein important for blood clotting.
  • Only **male** patients can participate. Female patients are not eligible.
  • Patients who are not within the age range of **1 to less than 75 years** cannot participate.
Clinical Trials Concierge

Prefer not to search? Our Concierge searches the trials for you.

Tell us about your condition – we search every trial in Europe and connect you with the right site.

We usually reply within a few days

Verified sites

All sites with verified contact details – recruitment status may not be available; ask directly

Trial locations

Where you can join this trial

Countries are shaded by recruitment status. Click a recruiting country to ask about joining there.

RecruitingNot yet recruitingNot recruiting
Not finding your country?

Not sure what to do next?

Joining a clinical trial can seem overwhelming. We guide you step by step, so you know exactly what to expect and how we support you through the process.

See the full process and FAQ

Investigated drugs

Marstacimab is a medication being studied for its potential to help people with hemophilia, a condition where blood doesn't clot properly. This medication is designed to be used as a long-term treatment to prevent bleeding episodes in people with severe hemophilia A or moderately severe to severe hemophilia B. It works by helping the blood to clot more effectively, which can reduce the risk of bleeding. The study is looking at how safe and well-tolerated marstacimab is when used over a long period, as well as how effective it is in preventing bleeding in people with hemophilia, whether or not they have developed inhibitors, which are substances that can make treatment less effective.

What is already known about the treatment

Marstacimab – Marstacimab is administered as a prophylactic treatment for individuals with severe hemophilia A or moderately severe to severe hemophilia B, with or without inhibitors. It is currently being studied in clinical trials to assess its long-term safety, tolerability, and effectiveness. The medication works by targeting specific proteins involved in blood clotting, helping to prevent bleeding episodes. Marstacimab is classified as a therapeutic agent for blood disorders, specifically designed to manage hemophilia.

Investigated diseases

  • Hemophilia A

    Hemophilia A is a genetic disorder caused by a deficiency of clotting factor VIII, which leads to prolonged bleeding. This condition primarily affects males and is characterized by spontaneous bleeding episodes, particularly into joints and muscles. Over time, repeated bleeding into joints can cause joint damage and pain. The severity of the disease varies, with severe cases having less than 1% of normal factor VIII activity. Individuals with this condition may experience frequent nosebleeds, easy bruising, and excessive bleeding after injuries or surgeries. The progression of the disease can lead to chronic joint problems and reduced mobility if not managed properly.

  • Hemophilia B

    Hemophilia B is a genetic disorder resulting from a deficiency of clotting factor IX, leading to prolonged bleeding. Like Hemophilia A, it primarily affects males and is characterized by spontaneous bleeding episodes, especially into joints and muscles. The severity of Hemophilia B varies, with severe cases having less than 2% of normal factor IX activity. Repeated bleeding into joints can cause joint damage and chronic pain over time. Individuals with this condition may experience frequent nosebleeds, easy bruising, and excessive bleeding following injuries or surgeries. Without proper management, the disease can lead to chronic joint issues and decreased mobility.

Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2022-500470-33-00Protocol codeB7841007Estimated enrolment230 patientsSponsorPfizer Inc.

sourced from the EU Clinical Trials Register and site verification

Want to learn more about this trial or check if you can participate?

Clinical Trials Concierge

Prefer not to search? Our Concierge searches the trials for you.

Tell us about your condition – we search every trial in Europe and connect you with the right site.