Marstacimab

Marstacimab (brand name Hympavzi) is used to help prevent or reduce bleeding episodes in adults and children aged 6 years and older with hemophilia A (with or without factor VIII inhibitors) or hemophilia B (with or without factor IX inhibitors). It is given as an injection under the skin once a week using a marstacimab prefilled pen or a prefilled syringe.

Marstacimab works by targeting the Kunitz 2 domain of tissue factor pathway inhibitor (TFPI), which is a natural protein that helps prevent blood clots. Marstacimab is a new option for managing hemophilia A and B, especially for those who have developed inhibitors to FVIII and FIX. You may still need factor replacement therapies to manage any unexpected bleeding episodes. Marstacimab is part of a class of drugs known as tissue factor pathway inhibitor (TFPI) antagonists.

Marstacimab was approved by the FDA on October 11, 2024. It is the first anti-TFPI approved in the U.S. for hemophilia A or B and the first to be given under the skin using a pre-filled auto-injector pen or syringe.

Before starting marstacimab, it is very important to discuss with your healthcare provider about using factor VIII and factor IX products or bypassing agents (these are products that help blood clot but work differently from marstacimab).

Your healthcare provider may prescribe factor VIII, factor IX medicines, or bypassing agents to treat breakthrough bleeding episodes while you are being treated with marstacimab. Make sure to follow your healthcare provider’s instructions regarding when and how to use these medicines and the prescribed dose during your treatment with marstacimab. Do not use extra doses of marstacimab to treat breakthrough bleeds.

Tell your doctor if you are also using factor or non-factor based medicines. Your healthcare provider will give you instructions on how to stop your current treatment when switching to marstacimab.

Tell your doctor if you have or have ever had:

• a planned surgery;
• serious infection, sepsis (a severe reaction to an infection); or
• recent injury or trauma.

May harm an unborn baby. You may need a pregnancy test to confirm that you are not pregnant. Use effective birth control while using marstacimab and for at least 2 months after your last dose. Tell your doctor if you become pregnant.

Ask a doctor if it is safe to breastfeed while using marstacimab.

Common Side Effects

The most common side effects of marstacimab are:

• swelling, hardening, redness, bruising, bleeding, and pain at the injection site
• joint pain
• diarrhea
• headache
• itching
• fever
• rash.

Serious side effects and warnings

Marstacimab may cause the following serious side effects:

• Blood clots (thromboembolic events). Marstacimab may increase your risk for blood clots (thromboembolic events) in blood vessels of your arm, leg, lung, or head, which may be life-threatening. Get medical help right away if you develop any of these signs or symptoms of blood clots: swelling or pain in arms or legs, redness or discoloration in your arms or legs, shortness of breath, pain in the chest or upper back, fast heart rate, cough up blood, feel faint, headache, numbness in your face, eye pain or swelling, trouble seeing.
• Allergic reactions, including rash and itching, have happened in people treated with marstacimab. Stop using marstacimab and get medical help right away if you develop any of the following symptoms of a severe allergic reaction: swelling of your face, lips, mouth, or tongue, trouble breathing, wheezing, dizziness or fainting, fast heartbeat or pounding in your chest, sweating.

Marstacimab may harm an unborn baby. Pregnant women should not take marstacimab, and females with childbearing potential should use effective contraception during treatment with marstacimab and for 2 months after the last dose.

It is not known if marstacimab is safe and effective in people receiving ongoing Immune Tolerance Induction (ITI).

It is not known if marstacimab is safe and effective in children younger than 6 years old.

These are not all of the possible side effects of marstacimab. Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

Follow all directions on your prescription label and read all medication guides or instruction sheets. Use the medicine exactly as directed.

Marstacimab is injected under the skin, usually once every week.

Your healthcare provider will show you where to inject marstacimab. Do not inject into the same place two times in a row.

Prepare an injection only when you are ready to give it. Call your pharmacist if the medicine looks cloudy, has changed colors or has particles in it.

Throw away a prefilled syringe after one use, even if there is still medicine left inside.

If you need surgery, tell the surgeon ahead of time that you are using marstacimab. You will need to stop using the medicine for a short time.

Do not use marstacimab to treat breakthrough bleeding. You may be given other medicines to treat breakthrough bleeding during treatment with marstacimab. Follow your doctor's instructions very carefully.

Call your doctor if your symptoms do not improve, or if they get worse.

Store this medicine in the original container in the refrigerator. Protect from light and do not freeze or shake the medicine.

Do not warm the medicine with hot water, sunlight, or a microwave.

Take the medicine out of the refrigerator and let it reach room temperature before using.

You may store this medicine at room temperature for up to 7 days. Throw the medicine away if not used within 7 days. Do not put it back into the refrigerator.

Use the medicine as soon as you remember, and then return to your usual schedule. Do not take two doses at the same time.

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Do not inject into areas where the skin is tender, bruised, red, or hard. Avoid injecting into skin that has scars or stretch marks.

Other drugs may affect marstacimab, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell your doctor about all other medicines you use.

Find detailed information on biosimilars for this medication.