Population pharmacokinetic modeling of steady state carbamazepine clearance in children, adolescents, and adults.

Carbamazepine (CBZ) clearance decreases from childhood to adulthood and the factors determining this change could include age, size, autoinduction, or maturational changes. This study aims to describe the population pharmacokinetics of CBZ in children and young adults and test the hypothesis that CBZ clearance correlates with weight, surface area, and age. CBZ therapeutic drug monitoring data (sparse data) were collected from child and adult epileptics, and rich data were obtained from a bioequivalence study of CBZ in young adults. Population pharmaco-kinetic analysis was performed using NONMEM V. Forward stepwise, multiple regression was performed on the covariates. Bootstrap validation was performed. A total of 946 observations from 91 subjects, ages 0.7-37 years, were collected and analyzed. A one-compartment, first-order absorption and elimination model, with exponential interindividual error and additive residual error models was developed. The population model was: Clearance (Lhr-1) = ((2.24 x Surface area (m2)) + (0.047 x Dose (mg.kg-1)); Volume of distribution (L) = 0.37 x weight (kg); Absorption rate constant = 0.013 (hr-1). CBZ clearance increased with surface area and dose.