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Paclitaxel is a good compound for regional (intraperitoneal) chemotherapy of peritoneal carcinomatosis. During IPEC, a cytotoxic solution is circulated in the peritoneal cavity, thereby promoting close contact between the cytotoxic agent and the exposed (residual) tumour tissue. To further explore the role of PTX in this type of treatment and study the impact of treatment modalities on tumour tissue penetration, in-vivo animal experiments were set-up. In literature, PTX tumour uptake is frequently studied using autoradiography and/or fluorescence microscopy techniques. Owing to their semi-quantitative nature on one hand and the difficulty of incorporating imaging data within a pharmacokinetic-pharmacodynamic modelling framework on the other hand, we set out to develop a validated assay for the quantification of PTX in tumour tissue samples. Furthermore, in order to maximise spatial resolution, care was taken to minimise the sample weight necessary for the analysis. Based on an enzymatic tumour tissue digestion protocol, an easy, less labour-intensive, when compared to mechanical tissue disruption techniques, method was developed. Through validation experiments we showed that our method reliably quantifies PTX in a working range of 30-8000 ng/g tumour tissue. Finally, using samples from the in-vivo experiments we demonstrated the suitability of the developed method.

Little is known about the influence of hepatic pathologies on cytochrome P450 (CYP) mediated drug metabolism in children. The determination of the abundance of the different isoforms in pediatric microsomes may provide valuable information on the mechanisms of possible changes in activity. Until now, western blotting was mostly used for abundance measurements, but this technique only provides semi-quantitative data. Therefore, this study aimed to develop and validate an indirect ELISA for the quantification of the most important CYP isoform, CYP3A4, in human liver microsomes, using commercially available reagents. Samples, calibrators and validation samples were diluted to a final concentration of 10 μg microsomal protein/ml. A polyclonal antibody raised against the full length human protein was used as primary antibody; horseradish peroxidase conjugated secondary antibodies for detection. The assay was validated for sensitivity, working range and calibration, accuracy and precision. Amounts of CYP3A4 between 2 and 300 pmol/mg microsomal protein could be quantified with a 5-parameter logistics function with 1/x weighting factor. Coefficients of variation of intra and inter assay variability were between 9.54 and 13.98% (16.34% at LLOQ), and between 10.51 and 14.55% (19.44% at LLOQ), respectively. The relative error (%RE) varied between -5.96 and 6.68% (11.53% at LLOQ), and the total error between 11.93 and 21.23% (30.97% at LLOQ). The cross-reactivity of the method with human CYP2E1 showed to have no significant effect on the accuracy of the results. Successful analysis of five samples from an ongoing study demonstrated the usefulness of the method.

A fast and sensitive UPLC-MS/MS method was developed and validated for the simultaneous quantification of six probe metabolites for the in vitro cytochrome P450 activity determination in hepatic microsomes from patients with hepatic impairment. The metabolites acetaminophen (CYP1A2), 4'-hydroxy-mephenytoin (CYP2C19), 4-hydroxy-tolbutamide (CYP2C9), dextrorphan (CYP2D6), 6-hydroxy-chlorzoxazone (CYP2E1) and 1-hydroxy-midazolam (CYP3A4), together with the internal standard chlorpropamide, were separated on a Waters Acquity UPLC BEH C18 column (50 mm × 2.1mm, 1.7 μm particle size) with VanGuard pre-column (5 mm × 2.1mm, 1.7 μm particle size). A short gradient elution (total run time of 5.25 min), using water with 0.1% formic acid (eluent A) and acetonitrile with 0.1% formic acid (eluent B) at a flow rate of 400 μl/min, was used. The metabolites were detected with a triple quadrupole mass spectrometer in the multiple reaction monitoring mode. Two runs, one in the positive ionization mode and one in the negative mode, were necessary for the detection of all metabolites. The method was selective and showed good accuracy (84.59-109.83%) and between-day (RSD%

Monitoring of plasma antibiotic concentrations is necessary for individualization of antimicrobial chemotherapy dosing in special patient populations. One of these special populations of interest are the post-bariatric surgery patients. Until today, little is known on the effect of this procedure on drug disposition and efficacy. Therefore, close monitoring of antimicrobial plasma concentrations in these patients is warranted. A fast and uniform ultra-high-performance liquid chromatography (UPLC) method with tandem mass spectrometric detection (MS/MS) has been developed and qualified for the simultaneous quantification of β-lactam antibiotics in human plasma. Compounds included in this multi-component analysis are: amoxicillin, ampicillin, phenoxymethylpenicillin, piperacillin, cefuroxime, cefadroxil, flucloxacillin, meropenem, cefepime, ceftazidime, tazobactam, linezolid and cefazolin. After spiking of five different stable isotope labelled internal standards, plasma samples were prepared for UPLC-MS/MS analysis by mixed-mode solid phase extraction. The developed method was proven to be free of (relative) matrix effects and proved to be reliable for the quantification of 12 out of 13 β-lactam antibiotics. As a proof of concept the method has been applied to plasma samples obtained from a healthy volunteer treated with amoxicillin. The analytical method is suitable for use in a therapeutic drug monitoring setting, providing the clinician with reliable measurements on β-lactam antibiotic plasma concentrations in a timely manner.