Purpose: To evaluate the accuracy of prediction of Midazolam absorption and bioavailability in a pediatric population from in silico, in vitro and adult in vivo data. The significance of scaling of the clearance and gastrointestinal tract model parameters to appropriate age was assessed.
Methods: GastroPlus™ 5.0 with the PBPKPlus™ Module was used to simulate the adult human Cp-Time profiles for Midazolam in oral solution dosage forms. Simulated Cp-Times were compared to corresponding literature data in order to validate the non-linear dose dependence and bioavailability due to saturable CYP3A4 metabolism. The Population Estimates for Age-Related (PEAR) Physiology™, a part of PBPKPlus, was used to generate tissue parameters for adult and pediatric patients. Literature data for gut CYP3A4 distribution and in vitro Km and V max values were used along with rat tissue:plasma partition coefficients and in silico estimation of remaining biopharmaceutical and pharmacokinetic properties.
Results: Using the default ACAT model and the observed expression levels of CYP3A4 in liver and gut, PBPK simulations accurately reproduced the non-linear dose dependence for Midazolam bioavailability and Cp-Time profiles for po administration of Midazolam in adult patients. Using a purely in silico calculation of pediatric physiology, and scaling of the gastrointestinal tract parameters and metabolism to a pediatric population, pediatric Cmax and Tmax were also accurately simulated.
Conclusions: In-vitro data or in-vivo Cp-Time profiles from an adult population can be successfully used to predict the CpTime profiles in pediatric patients if the PEAR Physiology for a given age is accompanied by scaling of the gastrointestinal tract parameters and enterocyte metabolism to the same age.
AAPS Annual Meeting and Exposition, November 6-10, 2005 Nashville, TN
By Michael B. Bolger, Jason Chittenden, Walter S. Woltosz