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Abstract: A rapid and sensitive liquid chromatography/tandem mass spectrometry (LC–MS/MS) method has been developed and validated for the quantitative determination of cabazitaxel, a novel tubulin-binding taxane, in 100μl aliquots of human lithium heparinized plasma with deuterated cabazitaxel as internal standard. The sample extraction and cleaning-up involved a simple liquid–liquid extraction with 20μl aliquots of 4% ammonium hydroxide, 100μl aliquots of acetonitrile and 1ml aliquots of n-butylchloride. Chromatographic separations were achieved on a reversed phase C18 column eluted at a flow-rate of 0.20ml/min on a gradient of acetonitrile. The overall cycle time of the method was 5min, with cabazitaxel eluting at 3.0min. The multiple reaction monitoring transitions were set at 836>555 (m/z), and 842>561 (m/z) for cabazitaxel and the internal standard, respectively. The calibration curves were linear over the range of 1.00–100ng/ml with the lower limit of quantitation validated at 1.00ng/ml. The within-run and between-run precisions, also at the level of the LLQ, were within 8.75%, while the accuracy ranged from 88.5 to 94.1%. As dilution of samples prior to extraction resulted in a loss of cabazitaxel of approximately 6.5% per dilution step, a second calibration curve ranging from 40.0 to 4000ng/ml was validated and was also linear. The within-run and between-run precisions in this range were within 4.99%, while the accuracy ranged from 95.8 to 100.3%. The method was successfully applied to samples derived from a clinical study. [Copyright &y& Elsevier]

Abstract: A rapid and sensitive ultra performance liquid chromatography/tandem mass spectrometry (UPLC–MS/MS) method has been developed and validated for the simultaneous quantitative determination of dextromethorphan (DM) and its metabolites dextrorphan (DX), 3-methoxymorphinan (3MM) and 3-hydroxymorphinan (3HM), in human lithium heparinized plasma. The extraction involved a simple liquid–liquid extraction with 1ml n-butylchloride from 200μl aliquots of plasma, after the addition of 20μl 4% (v/v) ammonium hydroxide and 100μl stable labeled isotopic internal standards in acetonitrile. Chromatographic separations were achieved on an Aquity UPLC® BEH C18 1.7μm 2.1mm×100mm column eluted at a flow-rate of 0.250ml/min on a gradient of acetonitrile. The overall cycle time of the method was 7min, with elution times of 1.3min for DX and 3HM, 2.8min for 3MM and 2.9min for DM. The multiple reaction monitoring transitions were set at 272>215 (m/z), at 258>133 (m/z), at 258>213 (m/z) and at 244>157 (m/z) for DM, DX, 3MM and 3HM, respectively. The calibration curves were linear (r 2 ≥0.995) over the range of 0.500–100nM with the lower limit of quantitation validated at 0.500nM for all compounds, which is equivalent to 136, 129, 129 and 122pg/ml for DM, DX, 3MM and 3HM, respectively. Extraction recoveries were constant, but ranged from 39% for DM to 83% for DX. The within-run and between-run precisions were within 11.6%, while the accuracy ranged from 92.7 to 110.6%. The applicability of the bioanalytical method was demonstrated and is currently implemented in a clinical trial to study DM as probe-drug for individualized tamoxifen treatment in breast cancer patients. [ABSTRACT FROM AUTHOR]

P450 oxidoreductase (POR) is essential for cytochrome P450 (CYP) activity in humans. The POR∗28 allele (A503V) has been shown to impact on in-vitro CYP-mediated metabolism, including CYP3A isoenzymes. The aim of the present study was to determine the in vivo impact of the POR∗28 allele on the pharmacokinetics of the classic CYP3A phenotyping probes midazolam and erythromycin. Whereas midazolam is metabolized by both CYP3A4 and CYP3A5, erythromycin is exclusively oxidized by CYP3A4.To assess CYP3A activity, 108 cancer patients received midazolam and 45 others underwent the erythromycin breath test. Patients were genotyped for POR∗28, CYP3A4∗22 and CYP3A5∗3.In patients expressing CYP3A5, POR∗28 carriers showed 45% lower midazolam metabolic ratios compared with POR∗1/∗1 patients (P<0.001). This is in line with a lower CYP3A5 activity toward midazolam for POR∗28 carriers. In CYP3A5 nonexpressers, POR∗28 had no influence on midazolam pharmacokinetics. For erythromycin, POR∗28 carriership did not influence its metabolism.Our data show that the POR∗28 allele is associated with a lower in vivo CYP3A5 activity, but has no effects on CYP3A4-mediated erythromycin and midazolam metabolism. [ABSTRACT FROM AUTHOR]