Influence of trastuzumab on epirubicin pharmacokinetics in metastatic breast cancer patients

Background: Anthracycline cardiotoxicity is increased by the contemporaneous administration of trastuzumab. The mechanism by which it occurs is as yet unknown. The aim of this study was to evaluate whether trastuzumab modifies the pharmacokinetics of epirubicin and its metabolites. Patients and methods: Women with HER2-positive metastatic breast cancer were treated with epirubicin 75 mg/m2 i.v. bolus followed by docetaxel 75 mg/m2 in a 1-h infusion, every 3 weeks for six cycles, and trastuzumab (once at 4 mg/m2 , then 2 mg/m2 weekly thereafter) in a 30-min infusion. Epirubicin pharmacokinetic data of seven patients were evaluated at the first cycle of therapy (baseline, with trastuzumab administered 24 h after epirubicin), and at the sixth cycle (i.e. 15 weeks after baseline, with trastuzumab administered immediately before epirubicin). Results: No pharmacokinetic change in the parent compound epirubicin was detected. The area under the plasma concentration–time curve (AUC0–24 h) was 1230 ± 318 [mean ± standard deviation (SD)] at the first cycle and 1287 ± 385 h·µg/l at the sixth. The mean (±SD) maximum plasma concentration (Cmax) and the terminal elimination half-life at the first cycle (1303 ± 490 µg/l and 12.5 ± 3.1 h, respectively) were similar to those obtained at the sixth cycle (1229 ± 580 µg/l and 11.5 ± 2.9 h, respectively). Pharmacokinetic data of epirubicin metabolites evaluated at the first and sixth cycle of chemotherapy were superimposable without any statistical difference. Conclusion: Enhanced anthracycline cardiotoxicity related to trastuzumab administration was not linked to pharmacokinetic interferences with epirubicin and its metabolites