Hympavzi (marstacimab)
An approved treatment for Hemophilia A and Hemophilia B.
The same compound appears under different names depending on the context. Here is how to identify Marstacimab wherever you encounter it, plus the key facts at a glance.
- Generic name
- Marstacimab
- Brand name
- Hympavzi
- Development code
- PF-06741086
- Drug class
- Anti-TFPI monoclonal antibody
- Manufacturer
- Pfizer
- How it's taken
- Given as a subcutaneous injection (under the skin) once a week.
A once-weekly subcutaneous injection that blocks TFPI, a natural anticoagulant protein, to restore clotting balance in people 6 and older with hemophilia A or B, with or without inhibitors. It is injected at home with a prefilled pen or syringe.
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Where Marstacimab fits
Subcutaneous prophylaxis option for hemophilia A or B, providing an alternative non-factor approach alongside emicizumab and concizumab.
How Marstacimab works
Hemophilia makes it hard for blood to clot because your body doesn't have enough of a specific clotting factor. Marstacimab takes a different approach: instead of replacing the missing factor, it blocks a protein called TFPI that normally prevents clotting. This allows your blood to form clots through an alternative route in your body's clotting system, helping prevent bleeding episodes without needing frequent infusions.
Mechanism: Monoclonal antibody that inhibits tissue factor pathway inhibitor (TFPI) to restore clotting balance
Side effects and safety
The most common side effects are injection site reactions (pain, itching, swelling, bruising, redness, or hardening), headache, and itching. The drug can increase the risk of blood clots (thromboembolic events), which could lead to stroke, heart attack, or deep vein thrombosis. Patients with existing risk factors for blood clots should discuss this carefully with their doctor. Serious allergic reactions can happen; if one occurs, stop Hympavzi and get emergency care. The label also warns that it may harm an unborn baby (females who can become pregnant should use effective birth control during treatment and for 2 months after the last dose) and that it raises the D-dimer and prothrombin fragment 1.2 blood tests, so these tests may not be reliable for checking for blood clots.
This is not a complete list of side effects. Talk to your doctor or pharmacist about what to expect and when to seek medical attention.
Taking Marstacimab
Given as a subcutaneous injection (under the skin) once a week. The first dose is a loading dose of 300 mg, followed by 150 mg weekly. The dose can be increased to 300 mg weekly in patients weighing 50 kg or more if bleeding control is not adequate. For children aged 6 to 11, the loading dose is 150 mg followed by 75 mg weekly, which can be raised to 150 mg weekly in children weighing 25 kg or more. Patients 12 and older may self-inject after training; a caregiver gives it to younger children. No routine blood test monitoring is required. Approved for patients aged 6 and older, with or without inhibitors.
Availability and cost
Only available as the brand-name product.
Anti-TFPI monoclonal antibody for subcutaneous self-injection. Novel non-factor biologic for hemophilia prophylaxis targeting the tissue factor pathway.
Help paying for Hympavzi
Pick your insurance to see which help fits. Drugmaker copay cards can't be used with Medicare, Medicaid or TRICARE; charity funds are the usual route there.
- Copay help
HYMPAVZI Co-pay Savings Program: eligible commercially insured patients may pay as little as $0, up to $15,000 per calendar year.
For: private insurance · source - Bridge or quick-start supply
Interim Care Rx: during insurance delays or denials, eligible commercially insured patients may get up to 12 months free (6 months in Minnesota and Rhode Island).
For: private insurance · source - Free medicine program
Pfizer Patient Assistance Program may provide free medicine to eligible uninsured or government-insured underinsured patients; income and household size apply.
For: no insurance, Medicare, Medicaid, TRICARE · source - Other support
Voucher Program: eligible patients new to HYMPAVZI may receive a free one-time 4-week supply, including the loading dose.
The official page does not say who qualifies. Ask the program. · source - Insurance and case manager help
Patient Case Managers explain insurance coverage and identify financial help; Patient Navigators connect patients to community support.
The official page does not say who qualifies. Ask the program. · source
Good to know: Co-pay card excludes Medicare, Medicaid, TRICARE, VA and other government programs. Free medicine comes through the Pfizer Patient Assistance Foundation, a separate entity (see Pfizer RxPathways).
- From a charity · Hemophilia Federation of AmericaHelping Hands Program fundOpen
Pays for: Emergency living expenses ($250 prepaid card, once per year; referral through HTC or member organization; does not cover medical bills, copays or premiums), up to $250 per year.
The foundation says: “The Helping Hands program is now open on a limited basis for 2026. Due to funding constraints, a maximum of 20 requests will be approved…” - From a charity · TotalAssist (formerly PAN Foundation)Hemophilia fundOpen
Pays for: Out-of-pocket costs for approved medications, up to $12,500 per year. Requires health insurance (any kind).
- From a charity · The Assistance FundHemophilia fundWaitlist
Pays for: Copays, coinsurance, deductibles and other health-related expenses.
The foundation says: “WAITLIST — Accepting Waitlist Patients. TAF is currently accepting requests to join the enrollment waitlist for this program. Waitlists a…”
Clinical trial results
The Phase 3 BASIS trial showed marstacimab reduced bleeding episodes by 92% compared to on-demand treatment and 35% compared to standard prophylaxis over 12 months. Joint bleeds were significantly reduced across all bleeding types including spontaneous, joint, and target joint bleeds.
Development history
Developed by Pfizer under the code PF-06741086, marstacimab received FDA Fast Track designation in 2019 for hemophilia with inhibitors. It was approved by the FDA on October 11, 2024, for hemophilia A and B without inhibitors in patients aged 12 and older, and shortly after in the EU in November 2024. In June 2026 the FDA expanded the label to patients with inhibitors and to children aged 6 to 11.
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Common questions about Marstacimab
▸What is Marstacimab (Hympavzi)?
A once-weekly subcutaneous injection that blocks TFPI, a natural anticoagulant protein, to restore clotting balance in people 6 and older with hemophilia A or B, with or without inhibitors. It is injected at home with a prefilled pen or syringe.
▸How does Marstacimab work?
Hemophilia makes it hard for blood to clot because your body doesn't have enough of a specific clotting factor. Marstacimab takes a different approach: instead of replacing the missing factor, it blocks a protein called TFPI that normally prevents clotting. This allows your blood to form clots through an alternative route in your body's clotting system, helping prevent bleeding episodes without needing frequent infusions.
▸What are the side effects of Marstacimab?
The most common side effects are injection site reactions (pain, itching, swelling, bruising, redness, or hardening), headache, and itching. The drug can increase the risk of blood clots (thromboembolic events), which could lead to stroke, heart attack, or deep vein thrombosis. Patients with existing risk factors for blood clots should discuss this carefully with their doctor. Serious allergic reactions can happen; if one occurs, stop Hympavzi and get emergency care. The label also warns that it may harm an unborn baby (females who can become pregnant should use effective birth control during treatment and for 2 months after the last dose) and that it raises the D-dimer and prothrombin fragment 1.2 blood tests, so these tests may not be reliable for checking for blood clots.
▸How is Marstacimab taken?
Given as a subcutaneous injection (under the skin) once a week. The first dose is a loading dose of 300 mg, followed by 150 mg weekly. The dose can be increased to 300 mg weekly in patients weighing 50 kg or more if bleeding control is not adequate. For children aged 6 to 11, the loading dose is 150 mg followed by 75 mg weekly, which can be raised to 150 mg weekly in children weighing 25 kg or more. Patients 12 and older may self-inject after training; a caregiver gives it to younger children. No routine blood test monitoring is required. Approved for patients aged 6 and older, with or without inhibitors.
▸Is Marstacimab FDA approved?
Yes, Marstacimab (Hympavzi) is FDA approved (2024) for the treatment of Hemophilia A and Hemophilia B.
▸How does marstacimab compare to concizumab?
Both are anti-TFPI monoclonal antibodies, but marstacimab (Hympavzi) is given once weekly while concizumab (Alhemo) requires daily injections. Since June 2026, marstacimab is approved for hemophilia A or B with or without inhibitors in patients 6 and older, so, like concizumab, it now covers patients both with and without inhibitors.
▸What is the dosing schedule for marstacimab?
For people 12 and older, treatment starts with a 300 mg loading dose, followed by 150 mg weekly; if bleeding control is inadequate and the patient weighs 50 kg or more, the dose can be increased to 300 mg weekly. For children 6 to 11, it starts with a 150 mg loading dose, followed by 75 mg weekly; if bleeding control is inadequate and the child weighs 25 kg or more, the dose can be increased to 150 mg weekly. It is injected under the skin with a prefilled pen or syringe; people 12 and older may self-inject after training, and a caregiver gives it to younger children.
▸Does marstacimab require routine blood test monitoring?
No routine blood test monitoring is required, which is an advantage over some other hemophilia treatments. However, patients should be monitored for thromboembolic events and should report any symptoms of blood clots to their doctor.
▸What did the BASIS trial show?
The Phase 3 BASIS trial demonstrated a 92% reduction in bleeding episodes compared to on-demand treatment and a 35% reduction compared to standard factor prophylaxis over 12 months. Joint bleeds were significantly reduced across all bleeding types.
▸Is marstacimab approved for patients with inhibitors?
Yes. In June 2026 the FDA expanded the label to people with hemophilia A or B with or without inhibitors, and lowered the age limit from 12 to 6.
▸What patient support is available for marstacimab?
Pfizer Hemophilia Connect provides one-on-one case manager support, insurance coverage assistance, financial assistance screening, and treatment education. A free starter supply may be available for eligible new patients.
▸Can marstacimab cause blood clots?
Yes, thromboembolic events are a known risk with marstacimab, as with other anti-TFPI therapies. Patients with existing risk factors for blood clots should discuss this carefully with their doctor before starting treatment.