Combined quantification of paclitaxel, docetaxel and ritonavir in human feces and urine using LC-MS/MS.

A combined assay for the determination of paclitaxel, docetaxel and ritonavir in human feces and urine is described. The drugs were extracted from 200 µL urine or 50 mg feces followed by high-performance liquid chromatography analysis coupled with positive ionization electrospray tandem mass spectrometry. The validation program included calibration model, accuracy and precision, carry-over, dilution test, specificity and selectivity, matrix effect, recovery and stability. Acceptance criteria were according to US Food and Drug Administration guidelines on bioanalytical method validation. The validated range was 0.5-500 ng/mL for paclitaxel and docetaxel, 2-2000 ng/mL for ritonavir in urine, 2-2000 ng/mg for paclitaxel and docetaxel, and 8-8000 ng/mg for ritonavir in feces. Inter-assay accuracy and precision were tested for all analytes at four concentration levels and were within 8.5% and <10.2%, respectively, in both matrices. Recovery at three concentration levels was between 77 and 94% in feces samples and between 69 and 85% in urine samples. Method development, including feces homogenization and spiking blank urine samples, are discussed. We demonstrated that each of the applied drugs could be quantified successfully in urine and feces using the described assay. The method was successfully applied for quantification of the analytes in feces and urine samples of patients.

High-performance liquid chromatographic analysis of felotaxel, a novel anti-cancer drug, in rat plasma and in human plasma and urine.

A high-performance liquid chromatographic method was developed for the determination of a new derivative of docetaxel, felotaxel, in rat plasma and human plasma and urine. The separation of felotaxel was performed on a Dikma C18 column with 0.2% formic acid and acetonitrile (50:50) as the mobile phase. The flow rate was 0.8 mL/min and the column effluent was monitored by an ultraviolet detector set at 275 nm. The method was validated and found to be linear in the range of 5-1,000 ng/mL. The lower limit of quantification was 5 ng/mL based on 100 µL of plasma. The variations for intra-day and inter-day precision were less than 6.9%, and the accuracy values were between 87.3 and 107.4%. The extraction recoveries were more than 80.5%. These data confirm that the developed method has satisfactory sensitivity, accuracy and precision for the quantification of felotaxel in rat plasma and in human plasma and urine. The method was successfully applied to a pharmacokinetics study of felotaxel after intravenous doses of 5 mg/kg in rats.

Identification of taxine derivatives in biological fluids from a patient after attempted suicide by ingestion of yew (Taxus baccata) leaves.

The yew tree (Taxus baccata) is an evergreen conifer that is widespread over central and southern Europe. The toxic effects of this conifer and its leaves have been known since ancient times. The seeds are generally responsible for accidental intoxications in childhood, whereas the bark and the leaves are mainly used for homicidal or suicidal attempts. We investigated the metabolic pattern of taxines in a healthy 44-year-old male farmer who was admitted to Bergamo Emergency Department after attempting suicide. High-performance liquid chromatography was used to separate and identify taxine metabolites. Data reported in this paper confirmed that the patient attempted suicide by ingesting Taxus baccata leaves, which had been suggested by clinical examination. The most abundant free and conjugated taxine metabolites were characterized. The high concentration of conjugated metabolites found in urine underscores the critical role that conjugation in the liver plays in eliminating taxines and increasing the probability of the patient's survival.

Influence of ketoconazole on the fecal and urinary disposition of docetaxel.

OBJECTIVE: The anticancer drug docetaxel is extensively metabolized by cytochrome P450 (CYP) 3A isozymes. Furthermore, docetaxel is also a substrate for the transmembrane ATP-binding cassette efflux transporter protein ABCB1. CYP3A-inhibition significantly reduces docetaxel total systemic clearance, on average by 50%. However, data on the effect of CYP3A-inhibition on the fecal and urinary excretion of docetaxel are lacking. To further elucidate the role of CYP3A- and ABCB1-mediated elimination pathways for docetaxel we investigated the effect of the potent CYP3A-inhibitor, and also ABCB1-inhibitor, ketoconazole on the fecal and urinary disposition of docetaxel in cancer patients. METHODS: Fifteen patients were treated with docetaxel (100 mg/m2), followed 3 weeks later by a reduced dose in combination with orally administered ketoconazole, or vice versa. Six patients were also administered [3H]-radiolabeled docetaxel. Fecal and urinary specimens, collected up to 72-h post-infusion, were analyzed for cumulative parent drug and radioactivity excretion. RESULTS: Ketoconazole coadministration increased fecal parent drug excretion twofold from 2.6 +/- 2.8 to 5.2 +/- 5.4% (mean +/- SD, P = 0.03) but did not affect urinary parent drug excretion (P = 0.69). The sum of fecal and urinary parent drug excretion was 5.3 +/- 3.0% for docetaxel alone and 7.8 +/- 5.6% in the presence of ketoconazole, respectively (P = 0.04). Total recovered radioactivity values were 45.8 +/- 19.1 and 32.4 +/- 19.7%, respectively (P = 0.23). CONCLUSION: CYP3A-inhibition by ketoconazole increases fecal parent drug excretion twofold in cancer patients. A more pronounced increase was not achieved, most likely due to concomitant intestinal ABCB1-inhibition.

Quantification of [3H]docetaxel in feces and urine: development and validation of a combustion method.

Most radiolabeled biological samples require extensive sample preparation to reduce quenching interference before quantification of radioactivity is possible. Clearly, a more rapid and simple method ensuring a constant count rate and optimal counting efficiency has important advantages. We report on the development and analytical method validation of a rapid and simple combustion method to quantify [3H]docetaxel excreted in human feces and urine. A 3-day validation procedure was performed; quality control (QC) samples, prepared in blank feces and urine, were combusted 5 times and aliquots of the produced tritiated combustion water were counted in a liquid scintillation counter. The validation runs demonstrated adequate precision (below 7.6%) across all QC levels. Sensitivity at the lowest QC level was excellent and recovery of radioactivity constant (ranging from 85 to 91.8%). Clinical applicability of the method was tested in a cancer patient receiving docetaxel and a tracer amount of [3H]docetaxel; during the first 72 h after [3H]docetaxel infusion, 60% of total radioactivity was excreted in the collected feces and urine, which is within the expected range. Combustion of tritiated feces and urine samples is a simple, rapid, sensitive, precise and reproducible method with high recovery. It can be applied to quantify [3H]docetaxel excretion after i.v. administration.