Effect of prothrombin complex concentrates on factor VIII inhibitor levels

Factor VIII inhibitor levels were measured on 261 occasions in 76 hemophilia-A inhibitor patients before and after prothrombin complex concentrate infusion at 13 treatment centers. A rise in inhibitor level to at least twice the pretreatment value occurred in 35 treatment episodes (13.5%), in 27 patients (36%). In 16 patients (21%), such an anamnestic immune response occurred with the first treatment. Factors predisposing to anamnestic responses may include patient idiosyncrasy, low pretreatment inhibitor levels, and exposure to concentrate over several days.