Pharmacokinetic studies of coagulation factors: relevance of plasma and extracellular volume and body weight

Summary. The clinical utility of pharmacokinetic (PK) studies of infused clotting factor concentrates in subjects with inherited coagulation disorders (e.g. haemophilia) remains unproven. In this regard, differences in drug distribution and elimination between very young children and older subjects is likely to be of importance, and there is preliminary information to suggest that the elimination half‐life of infused factor VIII (FVIII) is shorter in very young boys with haemophilia A as compared to older subjects. The cause for this difference is likely multifactorial and may relate, in part, to the relatively larger liver/whole body weight in very young children as compared to older children and adults. Since plasma volume correlates better with lean body mass than with observed weight in overweight/obese subjects, we suggest that the current practice of using observed weight for dosing of FVIII/IX concentrates be discontinued in subjects who are overweight/obese, and that dosing in such subjects be calculated using ideal weight for height.