How Bleeding is Stopped When a Person has an Inhibitor
People with inhibitors are not more prone to bleeding than other people with Hemophilia; however, because factor treatment is less effective, they may have more frequent bleeds than people who are taking factor prophylaxis and the bleeding may be more difficult to treat. One way to treat the bleed in a person with a very low titer inhibitor is to give the person large amounts of factor to overcome the inhibitor. This method may be used in a patient who is about to have surgery or when a bleed is life-threatening. The problem with this treatment is that after three to five days of treatment, the inhibitor level may rise even higher than before and take weeks, even months, to go down. This can cause problems if the person needs treatment again before the level drops. In most cases individuals with inhibitors will not have a sufficiently low titer to respond to higher doses of the missing factor.
For people with factor VIII deficiency (Hemophilia A), there is an FDA approved product called emicizumab that helps to both prevent and treat bleeds in patients with inhibitors. This has been a revolutionary medication for people with Hemophilia A who have inhibitors. Emicizumab does not work for factor IX deficiency (Hemophilia B). Unfortunately, there is no gene therapy option at this time for patients with inhibitors. There is research underway to investigate gene therapy as a potential option in the future to help with tolerance against inhibitors.
For both people with Hemophilia A and B, special medications known as “bypassing agents” can be used to treat bleeds. A bypassing agent is a special type of factor concentrate that uses other factor types to encourage the formation of blood clots, bypassing the need for factors VIII and IX. Because of this mechanism, these medications help stop the area of bleeding but also carry a risk of causing unwanted blood clots in other places. Two types of bypassing agents have been approved in the United States for this purpose: Activated Prothrombin Complex Concentrate (aPCC) and Recombinant FVIIa ("factor seven-a").
Activated Prothrombin Complex Concentrate (aPCC) is sold under the brand name FEIBAÒ. This is a "plasma-derived product", meaning that it is made from human blood. It is treated in several different ways to remove viruses and other contaminants. This product contains factors II, VII, IX, and X, with some of the factors already in their "activated” form. The other bypassing agent, recombinant Factor VIIa, is sold under the brand names NovoSevenÒ and SEVENFACTÒ. These medications are both recombinant factor concentrates made in a lab, not made from human blood.