Pharmacokinetics of Extended Half-Life Factor VIII Products By myPKFiT^R Is Useful for Personalized Treatment in Children with Severe Hemophilia a

Prophylactic administration of factor VIII products is necessary to prevent bleeding and preserve normal musculoskeletal function in children with severe hemophilia A (HA). Recently, extended half-life recombinant factor VIII (EHL-rFVIII) products have been utilized in HA patients. Therefore, the pharmacokinetics (PK) of EHL-rFVIII in individuals is needed to determine the appropriate administration for personalized prophylaxis according to the age, bleeding phenotype, the presence of arthropathy, and physical activity. The myPKFiT^R ver 3.0 has been developed as the device to estimate the personalized dosing with a 2 sample PK based on the population PK (Bayesian) tool. In this study we report our single-center experience to study PK profiles and to individualize dose and dosing interval based on myPKFiT^R. Eight patients with severe HA aged from 10 to 20 years were enrolled in this study for personalized prophylaxis. The half-life of EHL-rFVIII was approximately 15 to 18 hours in all patients studied. The clearance of FVIII was inversely correlated with the half-life of EHL-rFVIII. The EHL-rFVIII products have been basically administered twice a week. The trough levels of FVIII were more than 3% in all patients. The prophylactic regimen in adolescents was individually determined according to the personal simulation of PK study and to patients' life style and physical activities. Adolescent patients actively participated in sports, such as track and field, basketball, and football after school. The FVIII level after school was easily estimated by the use of myPKFiT^R according to the dose and duration of replacement. The doses of EHL-rFVIII products were individually determined to have more than 10 to 30% of FVIII level at the time of sports activity. During personalized prophylaxis (6 to 18 months), all of patients studied have been no bleeds during sports as well as no spontaneous bleeds. Additionally, myPKFiT^R has the capability of presenting the real-time FVIII level on the screen of smartphone after the replacement of EHL-rFVIII based on the individual PK. Some patients have referred their own FVIII level before the beginning of sports through their smartphone and then have decided the necessity of the replacement. These experiences suggest the enhancement of treatment concordance in the supportive relationship between patients and medical staff. Thus, the use of myPKFiT^R may be essential for the optimization of prophylactic administration of EHL-rFVIII and for the medical adherence and concordance in each individual.