Comparison of 1-Hour and 3-Hours Paclitaxel Infusion Pharmacokinetics: Results from a Randomized Trial

Purpose: Aim of this study was to characterize the difference in pharmacokinetics (PK) of paclitaxel (PAC) after 1-h and 3-h infusion in humans and to define a pharmacodynamic relationship between PAC PK and myelotoxicity. Patients and Methods: PAC PK were studied during the first PAC application in the first treatment cycle (1 treatment cycle = 6 PAC applications) in 25 patients. This patient group represents a subgroup of a large clinical study with neurotoxicity as primary endpoint. These 25 patients were those patients who were willing to give additional blood samples. The group size was sufficient for a full description of the PK of PAC. PAC was administered at 100 mg/m 2 weekly by 1-h (n = 12) or 3-h (n = 13) infusion to patients with advanced cancer (lung, breast, ovarian, cervix, and head and neck). Total PAC was quantified by high-performance liquid chromatography (HPLC). Pharmacokinetic parameters were calculated by noncompartmental and model-dependent methods. The leukocyte and neutrophil decrease during a 6-week treatment period was calculated by the percentage in decrease of white blood cell count (WBC) and absolute neutrophil count (ANC) as well as the area over the curve (AOC) of WBC and ANC. Results: The area under the curve (AUC), the plasma clearance (Clp), the volume of distribution at steady state (V ss ), the mean residence time (MRT) and the distribution half-life (t 1/2 ) of PAC tot were not different in the two application modes. The elimination half-life (t1/2) and maximum plasma concentration C max were significantly different. No significant differences in the percentage of reduction of WBC and ANC were seen. Calculation of AOC of WBC showed a borderline significant difference (p = 0.0547) in case of WBC and no significant difference in case of ANC between the two PAC schedules. A considerable variance of AOC was observed. Conclusion: The pharmacokinetic study of total PAC of the two schedules investigated showed significant differences in the elimination half-life, which is longer in case of the 1-h infusion of PAC and in the maximum plasma concentration, which is higher in case of the 1-h infusion. The two schedules showed a similar myelotoxicity with a trend of less toxicity in the 1-h procedure.