Population pharmacokinetic analysis of fexofenadine in Japanese pediatric patients

A population pharmacokinetic analysis was conducted to characterize the pharmacokinetics of fexofenadine in Japanese pediatric patients (6 months through 16 years) with perennial allergic rhinitis or atopic dermatitis. The dataset was composed of 515 patients (including 109 adults), for a total of 1,080 concentration–time points. The analysis was performed with NONMEM using the SAEM method. Several structural models and residual error models were evaluated. The relationship between the individual estimates and the potential covariates was then investigated: demographic and pathophysiologic characteristics were tested as potential model covariates (forward selection method). The qualification of the model was performed using visual predictive check and bootstrap. A two-compartment disposition model with first-order absorption best fitted the data. The inter-individual variability was modeled through an exponential error model for all parameters (except for ka for which no inter-individual term could be estimated), while a proportional error model was used to model the residual variability. The final model included two covariates on elimination clearance and one on the intercompartmental clearance. CL/F was related to BSA and patient’s age (expressed in months) Q/F was also related to BSA. Once the model was correctly qualified, exposure parameters such as C_max and AUC_τ were computed and compared between each age sub-group and between Japanese and Caucasians patients. These comparisons did not reveal any major difference (less than 50 %) between subgroups.