Factor VIII treatment works for most people with hemophilia A. Sometimes, however, the body’s immune system fights back against the treatment and prevents it from working properly.

What are Inhibitors?

  • FVIII inhibitors are neutralizing antibodies that develop in recipients following treatment
  • Incidence of inhibitor formation in newly treated patients with severe hemophilia A is approaching 30%1
  • Daily life and productivity of inhibitor patients is severely compromised1
    • Frequent bleeds result in joint damage and decreased orthopedic status2
  • Inhibitors dramatically increase cost of care

In some people treated with factor VIII replacement therapy, the body's immune system mistakes the therapy as a threat. In response, the immune system makes antibodies, or inhibitors, that attack the factor VIII. Inhibitors are a very serious problem because they prevent, or inhibit, factor VIII replacement therapy from controlling bleeding.3


When inhibitors occur, doctors often recommend immune tolerance induction (ITI) to “reset” the immune system.

Talk to your healthcare provider about your condition. Inhibitors can only be detected by a blood test.

References: 1. Witmer C and Young Y. Ther Adv Hematol. 2013. 4:59-72. 2. Scalone L Haemophilia. 2006. 12: 154-62. 3. Mannucci PM, Abshire T, Dimichele D, et al. Inhibitor development, immune tolerance and prophylaxis in haemophilia A—the need for an evidence-based approach. Haemophilia. 2006;12:429–434. 4. Hay CR. The epidemiology of factor VIII inhibitors. Haemophilia. 2006;12(suppl 6):23–29.