When your child has a bleeding disorder, you may have some questions about how to treat their bleeding disorder and what are the options for treatment. This page will go over all the information on one type of treatment class called rebalancing agents.

Anti-TFPI

What is this treatment for?
Anti-TFPI treatment is for people with hemophilia A or B, including those who have inhibitors. Inhibitors are a problem where the body blocks the usual treatment, making it harder to stop bleeds. Anti-TFPI is a newer option that helps prevent bleeding in a different way than factor replacement therapy.
How does this treatment work in the body?
TFPI stands for tissue factor pathway inhibitor. It’s something your child’s body makes to help control clotting. Anti-TFPI treatments are special medicines (called monoclonal antibodies) that block TFPI, so the body can make more thrombin—a key part of forming blood clots. This helps stop bleeding faster.
How is this treatment given?
Anti-TFPI treatments are given as shots under the skin, usually in the thigh or stomach. These are called subcutaneous injections. They come in prefilled pens or autoinjectors, which are easy to use at home.1
How much of the treatment is normally given?
  • The amount depends on the specific medicine and the child’s age and weight.
    One anti-TFPI medicine, called concizumab, is given every day.6
  • Another, called marstacimab, is given once a week.9
  • A health care provider will help decide the right dose and how often to take it.
Who can use this treatment?

Anti-TFPI treatments are made for:

  • People with hemophilia A or B
  • Some are for people who have inhibitors and some for those who don’t have an inhibitor, so check with your provider to learn what is right for you.
  • Teens and adults (Some brands are only approved for people 12 and older)
What are the benefits?
  • Fewer bleeds—both with and without injuries
  • Easy to use—you don’t need to find a vein
  • Works even if your child has inhibitors
  • Fewer treatments—once a day or once a week
What are the limitations, risks, or unknowns with anti-TFPI?
  • Some people may have mild side effects, like redness or itching where the shot was given, or headaches.6
  • There is still more to learn about long-term safety, since this is a new treatment.
  • These medicines might not work the same for everyone.
  • It may not be approved for all ages yet or available in every country.
  • It could be expensive, and insurance coverage might vary.
  • Because these medicines do not change how much factor is in the body, factor levels will remain the same.4
What are the other names for this treatment?
  • Hympavzi™ (marstacimab)
  • Alhemo® (concizumab)

siRNA

What is this treatment for?
siRNA treatment is for people with hemophilia A or B, whether they have Factor VIII or IX inhibitors or not. It helps reduce bleeds and is used by kids aged 12 and older and adults.8
How does this treatment work in the body?
siRNA (small interfering RNA) like fitusiran silences a gene that makes antithrombin, a protein that slows down blood clotting. By lowering antithrombin, it lets the body make more thrombin, which helps blood clot better and reduces bleeding.7
How is this treatment given?
Fitusiran is given by a shot under the skin (called a subcutaneous injection) at home every couple months.5
How much of the treatment is normally given?
The usual dose of fitusiran is one injection once every two months using the “antithrombin-based dosing” plan. Health care providers check antithrombin levels to find the right dose for each person.5
Who can use this treatment?

Fitusiran (Qfitlia) is approved for:

  • People aged 12 years and older
  • Those with hemophilia A or B
  • People with or without inhibitors
  • It is not approved for younger children yet5
What are the benefits?
  • Fewer bleeds: Studies show bleeds dropped up to 71–90% compared to older treatments.5
  • Long gaps between shots: one injection every two months.
  • Works for all hemophilia types, including those with inhibitors.3
  • No needles in veins, making it easier and more comfortable.
What are the limitations, risks, or unknowns with siRNA (fitusiran)?
  • Possible side effects:
    • Infections (like colds) and mild liver problems5
    • Blood clots if antithrombin drops too low. Health care provider will monitor these levels carefully5
    • Some people may get gallbladder issues, like gallstones or inflammation2
  • Still new: it's only recently approved (March 2025), and long-term safety is being studied.2
  • Not for kids under 12 at this time.7
  • Health care providers need to watch lab tests for antithrombin and liver enzymes regularly.5
References
  1. ClinicalTrials.gov. (2024). Phase 3 trials for concizumab and marstacimab. U.S. National Library of Medicine. https://clinicaltrials.gov/
  2. Food and Drug Administration. (2025, March 28). FDA approves novel treatment for hemophilia A or B, with or without factor inhibitors [Press release]. https://www.fda.gov/news-events/press-announcements/fda-approves-novel-treatment-hemophilia-or-b-or-without-factor-inhibitors
  3. Grossi, G. (2025). FDA approves fitusiran for reducing bleeds in patients with hemophilia A/B. American Journal of Managed Care. https://www.ajmc.com/view/fda-approves-fitusiran-for-reducing-bleeds-in-patients-with-hemophilia-a-b
  4. National Bleeding Disorders Foundation. (2025). Treatment options overview. https://stepsforliving.bleeding.org/
  5. National Center for Biotechnology Information. (n.d.). Antithrombin lowering in hemophilia: A closer look at fitusiran. PMC. https://www.ncbi.nlm.nih.gov/pmc/
  6. Novo Nordisk. (2024). Alhemo® (concizumab) prescribing information. https://www.novonordisk-us.com/
  7. Sanofi. (2025). Qfitlia prescribing information. https://www.sanofi.com/en/science-and-innovation/pipeline/qfitlia
  8. ScienceDirect. (n.d.). Fitusiran – an overview.https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/fitusiran
  9. U.S. Food and Drug Administration. (2024). Approval of Hympavzi™ (marstacimab). https://www.fda.gov/