Population pharmacokinetics of clomipramine, desmethylclomipramine, and hydroxylated metabolites in patients with depression receiving chronic treatment: model evaluation

Because metabolites play a major role in the clinical response to clomipramine, the objective of the current study was to develop a population model and evaluate its performance to describe the pharmacokinetic profiles of clomipramine (C) and its active metabolites desmethylclomipramine (DC), 8-hydroxy-clomipramine (OHC) and 8-hydroxy-desmethylclomipramine (OHDC). A first sample of 14 patients served for development of a 2-molecule C and DC model, which was shown to provide reasonable estimates of AUC-based clearances, as well as precise estimation of interindividual variability. Simulated data, generated to mimic a semi-rich sampling design and chronic treatment with clomipramine, indicated that clearance estimation was feasible under routine treatment conditions. A second sample of 30 patients, recruited prospectively and followed for a median 4-week period, was used to extend the 2-molecule model to a 4-molecule model. Goodness-of-fit assessment revealed that model-predicted concentrations were reasonably close to observed concentrations for a majority of patients. Interindividual variability was 50% to 60% for hydroxylation and desmethylation clearances, and residual variability was 30%. The proposed model incorporates much of what is known about the metabolism of clomipramine and may valuably integrate the influence of genetic and environmental factors on each metabolic pathway.