Pharmacokinetic Evaluation of Paclitaxel in South Indian Cancer Patients: A Prospective Study

Paclitaxel is a promising drug in the treatment of different solid tumors. It exhibits nonlinear pharmacokinetics, particularly when administered as a constant rate infusion for shorter duration (e.g., 3 h). Because of the nonlinearity, relatively small changes in dose may lead to large changes in peak plasma concentration and total drug exposure. The study was conducted to evaluate the pharmacokinetics of different doses of paclitaxel administered intravenously as an infusion. A prospective study was conducted in 23 cancer patients aged between 28 and 74 years, treated with paclitaxel (130, 200, 230, and 260 mg/m²) over 3 h as a constant rate infusion. Plasma samples were collected from all patients at 0, 1, and 3 h and for five patients at 5 and 13 h and paclitaxel concentrations were determined using high-performance liquid chromatography method. The overall mean clearance was found to be 47.5847 ± 142.028 l/h; the mean volume of distribution was 142.028 ± 73.438 l; mean elimination rate constant was 0.336 ± 0.002/h; mean half-life was 2.086 ± 0.009 h; mean area under the curve (AUC) was 5.5917 ± 2.707 mg/ml*h and the mean of mean residence time was 2.980 ± 0.0131 h. Paclitaxel showed nonlinear kinetics and the pharmacokinetic parameters calculated were similar to those quoted in the literature. The peak plasma concentration at 130 mg dose level was 2 μ/ml, but an increase in dose was not associated with proportional increase in plasma concentration. No significant difference was found between pharmacokinetic parameters such as clearance, volume of distribution, and AUC at different dose levels.