Topic Overview

What are inhibitors?

Some people who have hemophilia A develop antibodies to the injected clotting factor. The body thinks that the replacement clotting factors don't belong in the body, so it creates the antibodies, also called inhibitors, to get rid of them.

Inhibitors may make it harder to treat bleeding episodes because the body's natural defense system (immune system) interferes with the function of replacement clotting factors.

Some people produce few inhibitors; others produce many.

How can I be treated?

If you have inhibitors, hemophilia treatment may require specially engineered replacement clotting factors. Other treatment for clotting factor inhibitors includes therapy to suppress the immune system (immunosuppressive therapy).

If you have a larger amount of inhibitors, you might be treated with:

• Factor bypassing agents. These clotting factors are used to skip the part of the clotting process that requires either clotting factor VIII or IX. This treatment is unpredictable, and it is hard to determine the correct dose. This treatment also slightly increases your risk of having a heart attack or developing blood clots.
• A regimen that allows the body to get used to the clotting factor so that it won't produce as many or any inhibitors. This is done by giving large amounts of clotting factors daily over an extended period of time. During the first part of the treatment, you will get a factor bypassing agent along with the regular clotting factors to make sure that any injury will heal. Once the body starts getting used to the clotting factor, the bypassing agent is no longer needed.

If your body produces few inhibitors in reaction to clotting factors, you may use the treatments above. You also may be treated with:

• Large doses of the clotting factor, which can overwhelm the inhibitors.
• Factors taken from pig plasma (porcine factors). People with a lot of inhibitors who do not respond to human clotting factors often respond well to porcine factors.
• A clotting factor that is produced in a lab. Since it is man-made and does not come from human blood products, there are no risks of getting viral infections when it is injected.

If your body produces many inhibitors, you may be treated by pumping your blood through a machine that removes or neutralizes the inhibitors (plasmapheresis) to reduce or neutralize the inhibitors in the body. This process only works temporarily and is used before a surgery or after a major injury.