When people with hemophilia A, hemophilia B, or von Willebrand disease (VWD) use clotting factor replacement products as treatment to stop or prevent a bleeding episode, their immune system can fight against them by making antibodies. These antibodies are called inhibitors. An inhibitor is a type of antibody, that blocks or destroys the infused replacement factor product, which causes the treatment to not work. Anybody can get an inhibitor regardless of their disease severity (mild, moderate, severe) or age (newborn to the elderly). However, inhibitors are more common in people with Hemophilia A.

When inhibitors develop in people with hemophilia B, the experience is different than for those with hemophilia A. People with Hemophilia B with an inhibitor may start to experience allergic reaction(s) to their factor IX (9) treatment during or right after they get it. These reactions can be very serious, so it's essential to talk to the experts at your hemophilia treatment center about it.


Can I get an inhibitor?

If you are infusing clotting factor replacement products to prevent or treat a bleeding episode, you can develop an inhibitor. However, not everyone who uses these medications will develop an inhibitor. Some people are at a higher risk of developing an inhibitor. For example, people with severe hemophilia are more likely to develop an inhibitor than people with mild hemophilia. This could be because of the genetic mutation that causes their severe hemophilia or because people with severe hemophilia are more likely to use clotting factor than people with mild hemophilia.


Having an inhibitor makes it harder to stop a bleeding episode. The usual treatment doesn't work, so health care providers must try different methods and medications. Inhibitors can lead to serious bleeding that could be life-threatening. They may also cause lasting damage to the joints and create difficulties in the social, emotional, and financial parts of a person’s life.

To learn more information about inhibitors please visit the Facts About Inhibitors Booklet.