What Are the Subcutaneous Treatments for Hemophilia?

Yes, there are highly effective subcutaneous (under the skin) treatments for hemophilia, often referred to as non-factor therapies. Unlike traditional treatments that require intravenous (IV) infusions to replace the missing clotting factor, these medications use different mechanisms to help the blood clot and are given as subcutaneous injections (shots under the skin) ^[1][2][3]. They are used for routine prophylaxis—to reduce the frequency of bleeding episodes—and represent a significant quality-of-life improvement for many people, especially those who struggle with difficult venous access.

As of early 2025 in the United States, there are four main non-factor therapies approved by the FDA. Their use depends on whether you have Hemophilia A or B, and whether you have developed inhibitors (antibodies that the immune system creates to fight against replacement factor). These medications substantially reduce bleeding risk, though individual results vary and they do not guarantee complete protection from all bleeds ^[1][4][5].

Crucially: Never stop your current IV prophylaxis or change your doses while waiting to switch to a non-factor therapy without explicit instructions from your hemophilia treatment center.

Summary of Subcutaneous Non-Factor Therapies

(Note: Approvals and exact indications can differ outside the United States. Always consult your hemophilia treatment center for the most current options available to you.)

Emicizumab (Hemlibra)

Emicizumab is approved for routine prophylaxis in adults and children with Hemophilia A, both with and without inhibitors ^[6].

• How it works: It is a bispecific antibody, acting like a bridge. In Hemophilia A, factor VIII is missing. Emicizumab bridges activated factor IX and factor X together, mimicking the function of the missing factor VIII to help the blood clot ^[1][7].
• How it is given: After an initial four weeks of weekly loading doses, maintenance doses can be given once a week, every two weeks, or every four weeks as a subcutaneous injection ^[8].
• Medical Alert for Lab Tests: Emicizumab interferes with standard blood clotting tests, specifically the aPTT (activated partial thromboplastin time) and standard Factor VIII activity assays ^[9][10]. Because of the drug, these tests will falsely appear normal. A normal aPTT test does not prove you are adequately protected from bleeding and cannot be used to guide your treatment while taking emicizumab. Your medical team must use specific, emicizumab-compatible tests (like a bovine chromogenic assay, a specialized test that is not fooled by the drug) to accurately measure your clotting ability ^[11].

Fitusiran (Qfitlia)

Approved by the FDA in early 2025, fitusiran is used for routine prophylaxis in adults and children (12 years and older) with Hemophilia A or B, with or without inhibitors ^[12][13].

• How it works: Fitusiran is a small interfering RNA (siRNA) therapy (a medicine that lowers the production of specific proteins). It targets and reduces the production of antithrombin in the liver ^[2]. Antithrombin naturally prevents blood clots; lowering its levels shifts the balance to increase the generation of thrombin (a critical enzyme that helps blood clot) ^[2][14].
• How it is given: Dosing is individualized based on blood tests measuring your antithrombin activity. The approved regimen generally starts at one injection every two months. Your doctor must adjust the dose or frequency based strictly on your lab results; patients should never adjust this dose on their own ^[15][13].
• Monitoring: Patients require specific monitoring for liver and gallbladder health, as well as for the risk of dangerous blood clots ^[16][4]. Signs of liver or gallbladder complications include yellowing of the skin/eyes, severe abdominal pain, or unexplained nausea and vomiting.

Marstacimab

Approved in late 2024, marstacimab is for adults and children (12 years and older) with Hemophilia A or B who do not have inhibitors ^[17].

• How it works: Marstacimab is a monoclonal antibody targeting tissue factor pathway inhibitor (TFPI) ^[18]. TFPI normally slows down blood clotting. By blocking it, marstacimab enhances the body’s ability to form a clot ^[18][19].
• How it is given: It requires an initial loading dose, followed by a maintenance dose given as a subcutaneous injection once a week ^[20][5].

Concizumab (Alhemo)

Concizumab is another anti-TFPI therapy, but it is specifically indicated for patients (12 years and older) with Hemophilia A or B who have inhibitors ^[21][22].

• How it works: Like marstacimab, it blocks TFPI to increase thrombin generation and restore clotting ability ^[3].
• How it is given: It is given as a daily subcutaneous injection, with the dose adjusted by your doctor based on its plasma concentration (how much of the drug is currently in your blood) ^[22].
• Thrombosis Warning: Clinical trials for concizumab were temporarily paused due to severe blood clots. Strict adherence to dosing and rescue plans is required to minimize this risk ^[22][21].

Important Safety Considerations and Emergency Plans

While these therapies reduce the risk of bleeds, they do not treat active bleeding ^[23]. As with any injection, minor injection-site reactions can occur.

You must have a specific, written rescue plan for breakthrough bleeds or surgeries. If your plan instructs you to treat a bleed immediately at home, do not delay that prescribed rescue dose while waiting for a callback from your doctor ^[23]. However, you must use only the exact product and dose in that plan.

Why emergency medications need careful planning: While traditional factor replacement or bypassing agents (medicines that bypass the missing factor to form a clot) are used for rescue, combining them with non-factor therapies carries serious risks if not managed correctly. For instance, using high doses of aPCC (activated prothrombin complex concentrate, a specific type of bypassing agent) alongside emicizumab can cause life-threatening blood clots and damage to small blood vessels ^[23][24]. Because of this risk, aPCC is generally avoided with emicizumab. Rescue choices and dose limits also differ significantly when using fitusiran or concizumab to prevent dangerous blood clots ^[2][25].

When to Seek Immediate Emergency Care

• Signs of a serious bleed: Head injury, severe headache, confusion, neck or throat swelling, uncontrolled bleeding, severe or persistent abdominal pain, vomiting blood or black stools, blood in the urine, sudden painful muscle swelling, or an acutely painful or immobile joint.
• Signs of a blood clot (thrombosis): Chest pain, shortness of breath, sudden neurologic symptoms (like weakness on one side of the body, slurred speech, or facial drooping), or sudden swelling, pain, or redness in one arm or leg. Do not wait for a routine clinic callback if you have these symptoms—seek emergency care immediately.

What to Carry with You

Always carry a medical alert card, a phone record, or a bracelet that lists:

• Your exact hemophilia type and inhibitor status.
• The name of your non-factor therapy and the date of your last dose.
• Your specific written rescue plan.
• Emergency contact information for your hemophilia treatment center.

Show this to emergency, surgical, and anesthesia teams. For emicizumab patients, this card should explicitly state that standard aPTT tests will appear falsely normal and cannot be used to guide treatment ^[9].