Gemcitabine plus vinorelbine chemotherapy regimens: a pharmacokinetic study of alternate administration sequences

Objective: To investigate a possible pharmacokinetic interaction between gemcitabine (GEM) and vinorelbine (VNR), when co-administered following the alternate sequences GEM-VNR and VNR-GEM. Methods: Enrolled in this study were 31 patients with different advanced carcinoma: 9 patients were given GEM (I h i.v. infusion, 1000 mg/m(2)) followed after 5 min by VNR (10 min i.v. infusion, 25 mg/m(2)) (GEM-VNR sequence); 1:7 patients received VNR followed by GEM (VNR-GEM sequence), at the same doses and with the same infusion period; as a control group (GEM), 5 patients were given only single-agent gemcitabine (1 h i.v. infusion, 1000 mg/m(2)). Results: GEM serum levels showed higher C-max and AUC(tot) in the VNR-GEM protocol than in the GEM-VNR and GEM groups. The GEM pharmacokinetic profile in both schedules showed biphasic elimination, as in monotherapy. VNR concentration/time curves showed rapid plasma clearance and wide interpatient variability in both sequences. VNR C-max was higher in the VNR-GEM group than in GEM-VNR, while VNR AUC(tot) and Cl-tot did not differ significantly in the two sequences. Conclusions: Some pk-values were altered for both GEM and VNR, following the two alternate protocols. A possible rationale for this behaviour is that VNR and GEM may influence each other during liver elimination extraction and metabolism.