Purpose: The objectives of this study were to investigate the pharmacokinetics of intra-venous vinorelbine combined with lapatinib as well as the effect of covariates in breast cancer patients.
Methods: Women with HER2 + locally advanced or metastatic breast cancer progressing after ≤ 2 lines of trastuzumab-based treatment were treated with lapatinib per os starting 7 days (D) (D-7 to D0) before adding vinorelbine on a D1 & D8 every 3 weeks intravenous schedule. Lapatinib was given everyday. Dose levels [DL, lapatinib (mg)/vinorelbine (mg/m(2))] ranged from 750/20 to 1,250/25. A total of 29 patients, 37-76 years old, were treated with the combination of lapatinib + vinorelbine. For pharmacokinetic analysis, 7 time point samples were collected on D1 of cycle 1 for lapatinib and vinorelbine assays. For vinorelbine and lapatinib, respectively, whole blood and plasma concentrations were measured using ultra performance liquid chromatography with tandem mass spectrometry validated methods. Data analysis was performed using a non-linear mixed effect model program (Monolix version 3.1 s).
Results: A three-compartment open model adequately described vinorelbine pharmacokinetics. Body weight (BW) and platelet count significantly influenced blood vinorelbine clearance (CL). BW significantly influenced volume (V) and CL terms. Platelet count influenced vinorelbine elimination CL. The final parameter estimates were as follows: CL = 24.9 L/h, V1 = 8.48 L, Q2 = 50.7 L/h, V2 = 1,320 L, Q3 = 66.1 L/h, and V3 = 62.4 L (Qi and Vi denote inter-compartmental clearance and peripheral volume of distribution, respectively), normalized for a 70-kg patient according to BW allometric scaling (CL is normalized for a 250,000 platelet count). A one-compartment model with linear elimination adequately fitted the lapatinib plasma concentration-time data. The population pharmacokinetic parameters were CL = 27.7 L/h, V = 357 L, and the absorption constant, ka = 0.44 h(-1). The between-subject variabilities (BSV) could be well estimated for CL, V but not for ka. No covariate effect, including body surface area and vinorelbine dosage, could be identified for lapatinib.
Conclusions: The pharmacokinetic modeling of vinorelbine and lapatinib was consistent with the results previously reported. BW and platelet count were confirmed as influencing blood CL of vinorelbine. A pharmacokinetic interaction occurred between vinorelbine and lapatinib probably due to lapatinib inhibition of CYP450-3A4. The combined lapatinib administration decreases statistically significant the vinorelbine CL. The maximal tolerated dose for the combination of lapatinib with vinorelbine on a q3w schedule is as follows: lapatinib 1,000 mg/day continuously and vinorelbine 22.5 mg/m(2) D1 & D8.