Inhibitors to Factor XI in patients with severe Factor XI deficiency.

Factor XI (FXI) deficiency is a rare bleeding disorder that may arise from any of a number of missense, nonsense, splice site, insertion, and deletion mutations within the FXI gene. Severely affected patients are at considerable risk of developing inhibitors to FXI and, although spontaneous bleeding is uncommon in such patients, bleeding after surgery or trauma can be severe. As treatment with fresh frozen plasma (FFP) or FXI concentrates is ineffective in patients with inhibitors, other therapies must be sought. Traditionally, such patients have been treated with various agents and methods, including plasma exchange, cyclophosphamide, intravenous immunoglobulin, and prothrombin complex concentrates. However, emerging data indicate that recombinant activated factor VII (rFVIIa; NovoSeven, Novo Nordisk, Bagsvaerd, Denmark) may also be effective in FXI deficiency with inhibitors. Further work is required to determine the optimal dosing schedules of the agent in this indication.