Validation of a perioperative population factor VIII pharmacokinetic model with a large cohort of pediatric hemophilia a patients

Aims Population pharmacokinetic (PK) models are increasingly applied to perform individualized dosing of factor VIII (FVIII) concentrates in haemophilia A patients. To guarantee accurate performance of a population PK model in dose individualization, validation studies are of importance. However, external validation of population PK models requires independent data sets and is, therefore, seldomly performed. Therefore, this study aimed to validate a previously published population PK model for FVIII concentrates administrated perioperatively. Methods A previously published population PK model for FVIII concentrate during surgery was validated using independent data from 87 children with severe haemophilia A with a median (range) age of 2.6 years (0.03-15.2) and body weight of 14 kg (4-57). First, the predictive performance of the previous model was evaluated with MAP Bayesian analysis using NONMEM v7.4. Subsequently, the model parameters were (re)estimated using a combined dataset consisting of the previous modelling data and the data available for the external validation. Results The previous model underpredicted the measured FVIII levels with a median of 0.17 IU mL(-1). Combining the new, independent and original data, a dataset comprising 206 patients with a mean age of 7.8 years (0.03-77.6) and body weight of 30 kg (4-111) was obtained. Population PK modelling provided estimates for CL, V1, V2, and Q: 171 mL h(-1) 68 kg(-1), 2930 mL 68 kg(-1), 1810 mL 68 kg(-1), and 172 mL h(-1) 68 kg(-1), respectively. This model adequately described all collected FVIII levels, with a slight median overprediction of 0.02 IU mL(-1). Conclusions This study emphasizes the importance of external validation of population PK models using real-life data.