Inhibitors

Although treatments for haemophilia A and B using clotting factor replacement therapy are extremely effective, one of the most troublesome problems associated with them is that some people develop what are known as ‘inhibitors’ or ‘antibodies’. Inhibitors are produced by the body’s natural defence system if it starts to believe that the replacement clotting factor – much like a bacteria or virus – is harmful. Unfortunately, if this happens, the inhibitors produced inactivate the replacement clotting factors, rendering them useless.

What this means in practice is that people who develop inhibitors may not respond adequately to factor replacement therapy or may develop an increased bleeding tendency. During this time they might need to receive more intensive clotting factor therapy or have alternative treatments for a while, to allow the blood levels of the inhibitors to settle down.
On average around one third of people with severe haemophilia A develop inhibitors but fortunately this is much less common in severe haemophilia B (approximately 5-10 times lower). Unlike in haemophilia A, haemophilia B inhibitors are sometimes associated with the development of severe allergic reactions (anaphylaxis) to treatment with Factor IX concentrates. Management of these cases can be more complicated.

Please contact your Haemophilia Centre for more information.