Population pharmacokinetic analysis for simultaneous fit of clozapine and norclozapine concentrations in adult psychiatric patients

Abstract

Background: Clozapine (CLZ) exhibits a high potential for pharmacokinetic interactions due to its extensive and complex metabolism. Additionally, several patient-related factors contribute to the pharmacokinetic variability, making treatment optimization even more challenging. The goal of this study was to develop a parent-metabolite population pharmacokinetic model for CLZ and its primary metabolite norclozapine (NCLZ) and to evaluate sources of variability in a real-world clinical setting. Methods: Data from routine therapeutic drug monitoring (TDM) of 126 adult in- and out-patients with psychiatric disorders were used for the analysis. A nonlinear mixed-effects modeling approach was applied for data analysis to simultaneously fit CLZ and NCLZ concentrations. Results: A one-compartment model for the drug with an additional compartment for NCLZ was used to fit the concentration-time data. The population pharmacokinetic value of oral clearance for CLZ (CL/F) for a typical patient (female, non-smoker) was 26.4 L/h. Male sex and positive smoking status were associated with an increase in CL/F of 25.9 % and 29.2 %, respectively. The estimated value of metabolite clearance (CLm/F) for a typical patient was 29.6 L/h, while male sex and valproic acid (VPA) use were associated with its increases for 45.1 % and 95.5 %, respectively. Conclusion: The developed population pharmacokinetic model describes the simultaneous disposition of CLZ and NCLZ in adult psychiatric patients, accounting for impact of patient and co-therapy factors. In addition to the well-established effects of sex and smoking status on CLZ pharmacokinetics, the model characterizes the significant impact of VPA co-therapy, primarily on NCLZ disposition