Functional activity of rFIXFc and rFIX in FIX-deficient mice. FIX-deficient mice were dosed intravenously with rFIXFc at 219 IU/kg body weight (3 or 4 per group, 6 groups, n = 23) or rFIX at 200 IU/kg body weight (3 or 4 per group, 5 groups, n = 23) at time 0. Blood samples were collected at various times after dosing (0.25 hour to 96 hours) and analyzed for clotting activity with the use of FIX activity assay. *rFIX activity is undetectable in all of the mice at time points later than 48 hours after dosing.