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Hemophilia and “Inhibitors”

hemophiliaandinhibitors_wHemophilia is a bleeding disorder that interferes with the blood clotting process. Hemophilia A, also known as classic hemophilia, is the most common type – affecting one in 5,000 to 10,000 males worldwide. This condition is treated with infusions of clotting factor, which can either be derived from plasma or as a genetically engineered clotting product called recombinant factor.

Recombinant factor quickly gained popularity after it became available in 1992 for hemophilia A and is used by most people with hemophilia, in part because this form of clotting factor significantly decreases any chance of blood-borne infection. However, the risk of a hemophilia complication called “inhibitors” may still be present even with the use of recombinant factor.

With traditional plasma-derived clotting factor, some people develop an immune reaction that essentially targets the clotting factor as foreign. The immune system sends out “inhibitors” that interfere with the clotting factor’s function. This results in less effective treatment and more bleeding, pain, and joint damage for the patient. About 25 percent of those with severe hemophilia A develop inhibitors.

To better understand the comparative risk of inhibitors from plasma-derived and recombinant clotting factor, researchers examined inhibitor development in 574 children with severe hemophilia A. This study, published in the New England Journal of Medicine, found a higher than expected risk of inhibitors with recombinant factor in hemophilia A – basically the risk was the same with recombinant factor and plasma-derived factor. However, there was a difference between second-generation recombinant products and third-generation products: the third-generation products had a lower risk of leading to inhibitors in the young hemophilia A patients, according to these study results.

So is recombinant factor really no different than plasma-derived factor for patients?

Several additional experts have weighed in with opinions on this issue. For example, in a letter to the editors in the New England Journal of Medicine responding to the original study, Alfonso Iorio, M.D., Ph.D., Mark W. Skinner, J.D., and Mike Makris, M.D. wrote that they believe the risk from recombinant factor was overstated in the study.

“We anticipate obvious concerns in the hemophilia community regarding the unexpected finding of a higher rate of inhibitor development for second-generation recombinant factor VIII, and we would like to comment on the strength of the association,” notes Dr. Iorio and his colleagues in their letter. The crux of their concerns relate to the 20.4 percent of patients who were excluded from the original study and a risk ratio from the inhibitors that was less than 2, which they conclude “leave the association weak and questionable.”

Naturally, the issue of inhibitor development is hugely concerning for families with hemophilia and their healthcare providers. This is an important issue to examine, but there is simply not enough data yet to drawn clinically relevant conclusions. In the meantime, recombinant clotting factor remains the best treatment option for those with severe hemophilia.

Stephen C Vogt, PharmD
President and CEO BioPlus SP


Iorio A, Skinner MW, Makris M. Factor VIII products and inhibitors in severe hemophilia A. N Engl J Med 2013 Apr 11;368(15):1456.
Gouw SC, van der Bom JG, Ljung R, et al. Factor VIII products and inhibitor development in severe hemophilia A. N Engl J Med 2013 Jan 17;368(3):231-9.


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