What Are Inhibitors?

Inhibitors, A to B.

Inhibitors might seem mysterious. But understanding them better can help you understand your condition. And get on with life.

What's an inhibitor, anyway?2,3


  • People with hemophilia A or B can develop inhibitors, which prevent their factor VIII or IX treatment from working to form a clot to stop bleeding.

    People with hemophilia A or B can develop inhibitors, which prevent their factor VIII or IX treatment from working to form a clot to stop bleeding.
  • People with hemophilia lack certain clotting factor proteins necessary to control bleeds.

    Their treatment contains factor that replaces missing proteins and helps their blood clot.

    People with hemophilia lack certain clotting factor proteins necessary to control bleeds. Their treatment contains factor that replaces missing proteins and helps their blood clot.
  • But for some people, the factor may suddenly stop working—and antibodies are to blame.

    Antibodies are a part of your body's natural defense system, attacking foreign substances that enter the body. They're valuable for fending off viruses and bacteria.

    Antibodies are a part of your body’s natural defense system, attacking foreign substances that enter the body. They’re valuable for fending off viruses and bacteria.
  • For some people with hemophilia, these antibodies view the factor treatment as foreign and attack it, stopping it from working. The antibodies are called inhibitors.

    For some people with hemophilia, these antibodies view the factor treatment as foreign and attack it, stopping it from working. Those antibodies are called inhibitors.

  • People with hemophilia A or B can develop inhibitors, which prevent their factor VIII or IX treatment from working to form a clot to stop bleeding.

    People with hemophilia A or B can develop inhibitors, which prevent their factor VIII or IX treatment from working to form a clot to stop bleeding.
  • People with hemophilia lack certain clotting factor proteins necessary to control bleeds.

    Their treatment contains factor that replaces missing proteins and helps their blood clot.

    People with hemophilia lack certain clotting factor proteins necessary to control bleeds. Their treatment contains factor that replaces missing proteins and helps their blood clot.
  • But for some people, the factor may suddenly stop working—and antibodies are to blame.

    Antibodies are a part of your body's natural defense system, attacking foreign substances that enter the body. They're valuable for fending off viruses and bacteria.

    Antibodies are a part of your body’s natural defense system, attacking foreign substances that enter the body. They’re valuable for fending off viruses and bacteria.
  • For some people with hemophilia, these antibodies view the factor treatment as foreign and attack it, stopping it from working. The antibodies are called inhibitors.

    For some people with hemophilia, these antibodies view the factor treatment as foreign and attack it, stopping it from working. Those antibodies are called inhibitors.

Inhibitors can happen.

Inhibitors usually appear in young children. But they can develop at any age.4 Some people with hemophilia may be more at risk for getting inhibitors than others.

Severe hemophilia A
up to 3 out of every 10 people5

Hemophilia B
up to 1 out of every 20 people5

Who's most at risk for developing inhibitors?6

  • People with severe hemophilia
  • Children (inhibitors usually develop during childhood)
  • People with a family history of inhibitors
  • African-Americans and Hispanics (higher frequency of inhibitors)7

Some people with hemophilia A or B may develop inhibitors in response to a treatment that contains factor VIII or factor IX. Most inhibitors appear within the first 150 days of exposure to factor VIII.2,8

We don't know why some people get inhibitors and others don't, but scientists are trying to find out.

Complications: 5 things to know

1

Severe hemophilia patients with inhibitors don't bleed more often than other severe hemophilia patients. But their bleeds are more difficult to manage because they don't always respond to standard treatment.9

2

Inhibitor patients may develop serious complications, like uncontrollable bleeding, joint disease, and disabilities.4,10

3

Moderate and mild hemophilia patients may experience a change in bleeding pattern. They're also at risk for serious complications; many experience severe spontaneous bleeding in joints and muscles.11

4

Patients with inhibitors are at increased risk for life-threatening bleeding and are hospitalized more frequently.12

5

Surgeons may be reluctant to perform joint procedures and other operations meant to help improve an inhibitor patient's joint condition and mobility if they're concerned about uncontrollable bleeding.13

FEIBA. Made to help manage inhibitors.

Inhibitors aren't easy to understand. But they may be manageable.

Want to learn more? Check out our About FEIBA page.

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FEIBA [Anti-Inhibitor Coagulant Complex]
Indications and Detailed Important Risk Information for Patients

INDICATIONS FOR FEIBA [Anti-Inhibitor Coagulant Complex]

FEIBA is an Anti-Inhibitor Coagulant Complex indicated for use in hemophilia A and B patients with inhibitors for:

  • Control and prevention of bleeding episodes
  • Use around the time of surgery
  • Routine prophylaxis to prevent or reduce the frequency of bleeding episodes.

FEIBA is not indicated for the treatment of bleeding episodes resulting from coagulation factor deficiencies in the absence of inhibitors to coagulation factor VIII or coagulant factor IX.

DETAILED IMPORTANT RISK INFORMATION FOR FEIBA [Anti-Inhibitor Coagulant Complex]
WARNING: EVENTS INVOLVING CLOTS THAT BLOCK BLOOD VESSELS
  • Blood clots that block blood vessels and their effects have been reported during post-marketing surveillance following infusion of FEIBA, particularly following administration of high doses and/or in patients with a risk of forming blood clots.
  • If you experience any of these side effects, call your doctor right away.

You should not use FEIBA if:

  • You had a previous severe allergic reaction to the product (reactions causing discomforts that are damaging and life threatening)
  • You have signs of development of small blood vessel clots throughout the body
  • You have sudden blood vessel clots or blocked blood vessels, (e.g., heart attack or stroke)

Events involving blood clots blocking blood vessels can occur with FEIBA, particularly after receiving high doses and/or in patients with risk factors for clotting.

Infusion of FEIBA should not exceed a dose of 100 units per kg body weight every 6 hours and daily doses of 200 units per kg of body weight. Maximum injection or infusion rate must not exceed 2 units per kg of body weight per minute.

At first sign or symptom of a sudden blood vessel clot or blocked blood vessel (e.g., chest pain or pressure, shortness of breath, altered consciousness, vision, or speech, limb or abdomen swelling and/or pain), stop FEIBA administration promptly and seek emergency medical treatment.

Allergic-type hypersensitivity reactions, including severe, sometimes fatal allergic reactions that can involve the whole body, can occur following the infusion of FEIBA. Call your doctor or get emergency treatment right away if you get a rash, hives or welts, experience itching, tightness of the throat, vomiting, abdominal pain, chest pain or tightness, difficulty breathing, lightheadedness, dizziness, nausea or fainting.

Because FEIBA is made from human plasma it may carry a risk of transmitting infectious agents, e.g., viruses, the variant Creutzfeldt-Jakob disease (vCJD) agent and, theoretically, the Creutzfeldt-Jakob disease (CJD) agent.

The most frequent side effects observed during the prophylaxis trial were anemia, diarrhea, bleeding into a joint, signs of hepatitis B surface antibodies, nausea, and vomiting.

The serious side effects seen with FEIBA are allergic reactions and clotting events involving blockage of blood vessels, which include stroke, blockage of the main blood vessel to the lung, and deep vein blood clots.

Call your doctor right away about any side effects that bother you during or after you stop taking FEIBA.

Please see FEIBA full Prescribing Information.

You are encouraged to report negative side effects of prescription drugs to the FDA. Visit www.fda.gov/medwatch, or call 1-800-FDA-1088.