Large interindividual variability exists in the pharmacokinetics (PKs) of FVIII/FIX concentrates as demonstrated by Björkman et al among others.4, 5, 6To understand and predict the consequences of the interindividual variability of factor concentrates in individuals, population PK models have been constructed for prophylaxis4, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32and perioperative treatment33with standard half-life (SHL) and extended half-life (EHL) FVIII and FIX concentrates for hemophilia-A and -B patients, respectively. Here, F8 is linked to hemophilia A.