How blood coagulates to help stop a bleed

Meet factor VIII, a protein that is involved in one of the steps of the blood coagulating process. Factor VIII becomes factor VIIIa when an injury happens.

Blood Coagulation Process - HEMLIBRA® (emicizumab-kxwh) How HEMLIBRA Works MOA

Blood coagulation process continues normally

Factor VIIIa brings 2 other proteins (factor IXa and factor X) together, allowing the blood coagulation process to continue, stopping a bleed.

Blood coagulation process can’t continue normally

In people with hemophilia A who have low or missing factor VIII, the blood coagulation process cannot continue normally.

Coagulation is a natural process that helps the body stop a bleed.

VIII, IX, and X are the Roman numerals for 8, 9, and 10, respectively. Did you know that Roman numerals were used throughout Europe until the 14th century?

Blood coagulation process continues

HEMLIBRA acts like a bridge, bringing factor IXa and factor X together to allow the blood coagulation process to continue without needing to replace factor VIII.

HEMLIBRA is different from factor VIII.
Because HEMLIBRA is different from factor VIII, it works even in the presence of factor VIII inhibitors.

Laboratory studies show that when both factor VIIIa and HEMLIBRA are available, factor VIIIa binds to factors IXa and X more readily and tightly than HEMLIBRA.

Therefore, based on laboratory studies, overcoagulation was not observed when HEMLIBRA and factor VIII were present.


Find out about HEMLIBRA studies for people with and without inhibitors.

Our Account and Community Managers (ACMs) Are Here to Help

Your local ACM is part of your hemophilia community and is an expert on HEMLIBRA. ACMs are Genentech employees and do not provide medical advice. Talk to your doctor about your treatment options.

Important Safety Information & Indication


HEMLIBRA is a prescription medicine used for routine prophylaxis to prevent or reduce the frequency of bleeding episodes in adults and children, ages newborn and older, with hemophilia A with or without factor VIII inhibitors.

What is the most important information I should know about HEMLIBRA?

HEMLIBRA increases the potential for your blood to clot. People who use activated prothrombin complex concentrate (aPCC; Feiba®) to treat breakthrough bleeds while taking HEMLIBRA may be at risk of serious side effects related to blood clots.

These serious side effects include: 

  • Thrombotic microangiopathy (TMA), a condition involving blood clots and injury to small blood  vessels that may cause harm to your kidneys, brain, and other organs 
  • Blood clots (thrombotic events), which may form in blood vessels in your arm, leg, lung, or head  

Talk to your doctor about the signs and symptoms of these serious side effects, which can include: 

  • Confusion
  • Stomach, chest, or back pain
  • Weakness
  • Nausea or vomiting
  • Swelling, pain, or redness
  • Feeling sick or faint
  • Decreased urination
  • Swelling of arms and legs
  • Yellowing of skin and eyes
  • Eye pain, swelling, or trouble seeing
  • Fast heart rate
  • Numbness in your face
  • Headache
  • Shortness of breath
  • Coughing up blood

If you experience any of these symptoms during or after treatment with HEMLIBRA, get medical help right away. 

Carefully follow your healthcare provider’s instructions regarding when to use an on-demand bypassing agent or factor VIII, and the dose and schedule to use for breakthrough bleed treatment. If aPCC (Feiba®) is needed, talk to your healthcare provider in case you feel you need more than 100 U/kg of aPCC (Feiba®) total. 

Your body may make antibodies against HEMLIBRA, which may stop HEMLIBRA from working properly. Contact your healthcare provider immediately if you notice that HEMLIBRA has stopped working for you (eg, increase in bleeds).

The most common side effects of HEMLIBRA include: injection site reactions (redness, tenderness, warmth, or itching at the site of injection), headache, and joint pain. These are not all of the possible side effects of HEMLIBRA. You can speak with your healthcare provider for more information.

What else should I know about HEMLIBRA?

See the detailed “Instructions for Use” that comes with your HEMLIBRA for information on how to prepare and inject a dose of HEMLIBRA, and how to properly throw away (dispose of) used needles and syringes.

  • Stop taking your prophylactic bypassing therapy the day before you start HEMLIBRA
  • You may continue taking your prophylactic factor VIII for the first week of HEMLIBRA

HEMLIBRA may interfere with laboratory tests that measure how well your blood is clotting and create an inaccurate result. Speak with your healthcare provider about how this may affect your care. 

Medicines are sometimes prescribed for purposes other than those listed in a Medication Guide. Only use HEMLIBRA for the condition it was prescribed. Do not give HEMLIBRA to other people, even if they have the same symptoms that you have. It may harm them.

Tell your healthcare provider about all the medicines you take, including prescription medicines, over-the-counter medicines, vitamins, or herbal supplements. Keep a list of them to show your healthcare provider and pharmacist.

Before using HEMLIBRA, tell your healthcare provider about all of your medical conditions, including if you are pregnant, plan to become pregnant, are breastfeeding, or plan to breastfeed.

Since HEMLIBRA was tested in males, there is no information on whether HEMLIBRA may impact your unborn baby or breast milk. Females who are able to become pregnant should use birth control during treatment.

Side effects may be reported to the FDA at (800) FDA-1088 or You may also report side effects to Genentech at (888) 835-2555.

Please see Important Safety Information, including Serious Side Effects, as well as the HEMLIBRA full Prescribing Information and Medication Guide.