Personalized Dose of Adjuvant Imatinib in Patients with Gastrointestinal Stromal Tumors: Results from a Population Pharmacokinetic Analysis.

Purpose: Imatinib is the first-line treatment for patients with gastrointestinal stromal tumors (GIST) after surgery. However, its pharmacokinetic profile varies remarkably between individuals and has not been well characterized in postoperative Chinese patients with GIST. Therefore, this study aimed to develop a population pharmacokinetic (PPK) model and recommend appropriate doses for different patients to achieve the target trough concentration in such a population.

Patients And Methods: A total of 110 surgically treated GIST patients were enrolled, of which 85 were applied to conduct a PPK analysis with a nonlinear mixed-effect model and 25 for external validation of the model. Demographic and biomedical covariates, as well as six single nucleotide polymorphisms were tested to explore the sources of variation in pharmacokinetic parameters of imatinib. Monte Carlo simulations were performed to establish the initial dosing regimens.

Results: A one-compartment model was established in postoperative GIST patients. The red blood cell count (RBC) and rs2231142 were observed to have a significant effect on the clearance of imatinib. The typical values estimated by the final model were 9.72 L/h for clearance (CL/F) and 229 L for volume of distribution (V/F). Different from the fixed dose regimen of 400 mg each day, patients carrying rs2231142 heterozygous type and with a lower level of RBC (2.9 × 10/L), 300 mg imatinib daily is enough to achieve the target trough concentration. When RBC rises to 4.9 × 10/L, 500 mg daily is recommended. For patients with rs2231142 GG genotype, 500 mg a day is required at RBCs of 3.9 × 10/L and 4.9 × 10/L.

Conclusion: RBC and rs2231142 contribute to the pharmacokinetic variation of imatinib and personalized dose recommendations based on patient characteristics may be necessary.