Among the patients with hemophilia, 10∼15% have hemophilia B, and 1∼3% of the hemophilia B patients develop inhibitor to factor IX clotting activity. Allergic reactions to concentrates containing factor IX (FIX) are serious complications during the treatment of hemophilia B patients with inhibitor. Although treatment with recombinant activated factor VII (FVIIa) is generally recommended in these patients, it is limited by the agent's short half-life, a lack of experience with its use in this manner and the prohibitive cost. We report here on a case of a 9-year-old boy with severe hemophilia B with inhibitor and he had a history of anaphylaxis to FIX. The patient was successfully treated with a desensitization protocol with escalating doses of FIX in addition to administering premedications. (Korean J Hematol 2008;43: 179-183.)

Keywords: Hemophilia B, Inhibitor, Anaphylaxis, Desensitization