A rapid reversed phase high performance liquid chromatographic method for the determination of docetaxel (Taxotere) in human plasma using a column switching technique.

A rapid, simple and sensitive isocratic high performance liquid chromatography (HPLC) method was developed to measure the concentration of docetaxel in plasma samples with UV detection at 227 nm. The method uses a column switching technique with an Ultrasphere C18 column (75 x 4.6 mm ID, 3 mu, Altex, USA) as clean-up column and a CSC-nucleosil C8 column (150 x 4.6 mm ID, 5 mu, CSC, Montreal, Canada) as the analytical column. The mobile phase consisted of Phosphate buffer (30 mM, pH = 3)-acetonitrile (47:53, v/v) with the flow rates of 1.1 and 1.3 ml min-1 for clean-up and analytical columns, respectively. Paclitaxel was used as an internal standard. The plasma samples were extracted using a solid phase extraction method with Ammonium acetate (30 mM, pH = 5)-acetonitrile (50:50, v/v) as final eluent. The extraction method showed a recovery of 92% for docetaxel. In this system, the retention times of docetaxel and Paclitaxel were 7.2 and 8.5 min, respectively. The detection limit of docetaxel in plasma is 2.5 ng ml-1. This analytical method has a very good reproducibility (7.2% between-day variability at a concentration of 10 ng ml-1). It is applicable in clinical and pharmacokinetic studies.

A population pharmacokinetic model for docetaxel (Taxotere): model building and validation.

A sparse sampling strategy (3 samples per patient, 521 patients) was implemented in 22 Phase 2 studies of docetaxel (Taxotere) at the first treatment cycle for a prospective population pharmacokinetic evaluation. In addition to the 521 Phase 2 patients, 26 (data rich) patients from Phase I studies were included in the analysis. NONMEM analysis of an index set of 280 patients demonstrated that docetaxel clearance (CL) is related to alpha 1-acid glycoprotein (AAG) level, hepatic function (HEP), age (AGE), and body surface area (BSA). The index set population model prediction of CL was compared to that of a naive predictor (NP) using a validation set of 267 patients. Qualitatively, the dependence of CL on AAG, AGE, BSA, and HEP seen in the index set population model was supported in the validation set. Quantitatively, for the validation set patients overall, the performance (bias, precision) of the model was good (7 and 21%, respectively), although not better than that of the NP. However, in all the subpopulations with decreased CL, the model performed better than the NP; the more the CL differed from the population average, the better the performance. For example, in the subpopulation of patients with AAG levels > 2.27 g/L (n = 26), bias and precision of model predictions were 24 and 32% vs. 53 and 53%, respectively, for the NP. The prediction of CL using the model was better (than that of the NP) in 73% of the patients. The population model was redetermined using the whole population of 547 patients and a new covariate, albumin plasma level, was found to be a significant predictor in addition to those found previously. In the final model, HEP, AAG, and BSA are the main predictors of docetaxel CL.

Population pharmacokinetics of docetaxel during phase I studies using nonlinear mixed-effect modeling and nonparametric maximum-likelihood estimation.

Docetaxel, a novel anticancer agent, was given to 26 patients by short i.v. infusion (1-2 h) at various dose levels (70-115 mg/m2, the maximum tolerated dose) during 2 phase I studies. Two population analyses, one using NONMEM (nonlinear mixed-effect modeling) and the other using NPML (nonparametric maximum-likelihood), were performed sequentially to determine the structural model; estimate the mean population parameters, including clearance (Cl) and interindividual variability; and find influences of demographic covariates on them. Nine covariates were included in the analyses: age, height, weight, body surface area, sex, performance status, presence of liver metastasis, dose level, and type of formulation. A three-compartment model gave the best fit to the data, and the final NONMEM regression model for Cl was Cl = BSA(Theta1 + Theta02 x AGE), expressing Cl (in liters per hour) directly as a function of body surface area. Only these two covariates were considered in the NPML analysis to confirm the results found by NONMEM. Using NONMEM [for a patient with mean AGE (52.3 years) and mean BSA (1.68 m2)] and NPML, docetaxel Cl was estimated to be 35.6 l/h (21.2 lh-1 m-2) and 37.2 l/h with interpatient coefficients of variations (CVs) of 17.4% and 24.8%, respectively. The intraindividual CV was estimated at 23.8% by NONMEM; the corresponding variability was fixed in NPML in an additive Gaussian variance error model with a 20% CV. Discrepancies were found in the mean volume at steady state (Vss; 83.21 for NPML versus 1241 for NONMEM) and in terminal half-lives, notably the mean t1/2 gamma, which was shorter as determined by NPML (7.89 versus 12.2 h), although the interindividual CV was 89.1% and 62.7% for Vss and t1/2 gamma, respectively. However, the NPML-estimated probability density function (pdf) of t1/2 gamma was bimodal (5 and 11.4 h), probably due to the imbalance of the data. Both analyses suggest a similar magnitude of mean Cl decrease with small BSA and advanced age.

Pharmacokinetics of sparfloxacin in humans after single oral administration at doses of 200, 400, 600, and 800 mg.

The pharmacokinetics of sparfloxacin at oral doses of 200, 400, 600, and 800 mg were studied in 12 healthy volunteers in a randomized double-blind crossover study. Each dose administration was separated by a 1-week washout period. Plasma and urine samples were collected up to 120 hours postdosing, for determination of free and total (free plus glucurono-conjugated) sparfloxacin levels by high-performance liquid chromatography assay and ultraviolet detection. Mean Cmax values ranged from 705 +/- 158 to 1966 +/- 620 ng/mL for the 200 to 800 mg doses, at median tmax ranging from 4 to 5 hours. A slight decrease of sparfloxacin bioavailability with increasing dose was observed because AUC was 87% to 88% of the expected area when the dose was doubled. The elimination half-life values were constant over the dose range (with values ranging from 18 to 21 hours) as well as the renal clearance. The metabolic ratio conjugated/free drug was not modified by increasing dose.

Determination of Taxotere in human plasma by a semi-automated high-performance liquid chromatographic method.

A rapid, selective and reproducible high-performance liquid chromatographic (HPLC) method with ultraviolet detection was developed for the determination of the anti-cancer agent Taxotere in biological fluids. The method involves a solid-phase extraction step (C2 ethyl microcolumns) using a Varian Advanced Automated Sample Processor (AASP) followed by reversed-phase HPLC. The validated quantitation range of the method is 10-2500 ng/ml in plasma with coefficients of variation < or = 11%. The method is also suitable for the determination of Taxotere in urine samples under the same conditions. The method was applied in a phase I tolerance study of Taxotere in cancer patients, allowing the pharmacokinetic profile of Taxotere to be established.