Purpose: Measurement of endogenous uracil (U) is increasingly being used as a dose-individualization method in the treatment of cancer patients with fluoropyrimidines. However, instability at room... Show morePurpose: Measurement of endogenous uracil (U) is increasingly being used as a dose-individualization method in the treatment of cancer patients with fluoropyrimidines. However, instability at room temperature (RT) and improper sample handling may cause falsely increased U levels. Therefore we aimed to study the stability of U and dihydrouracil (DHU) to ensure proper handling conditions.Methods: Stability of U and DHU in whole blood, serum, and plasma at RT (up to 24 h) and long-term stability (>= 7 days) at - 20 degrees C were studied in samples from 6 healthy individuals. U and DHU levels of patients were compared using standard serum tubes (SSTs) and rapid serum tubes (RSTs). The performance of our validated UPLC-MS/MS assay was assessed over a period of 7 months.Results: U and DHU levels significantly increased at RT in whole blood and serum after blood sampling with increases of 12.7 and 47.6% after 2 h, respectively. A significant difference (p = 0.0036) in U and DHU levels in serum was found between SSTs and RSTs. U and DHU were stable at - 20 degrees C at least 2 months in serum and 3 weeks in plasma. Assay performance assessment fulfilled the acceptance criteria for system suitability, calibration standards, and quality controls.Conclusion: A maximum of 1 h at RT between sampling and processing is recommended to ensure reliable U and DHU results. Assay performance tests showed that our UPLC-MS/MS method was robust and reliable. Additionally, we provided a guideline for proper sample handling, processing and reliable quantification of U and DHU. Show less
The bioanalysis of the oral anticancer drug capecitabine and its metabolites has been investigated extensively over the past years. This paper reviews methods for the bioanalysis of capecitabine... Show moreThe bioanalysis of the oral anticancer drug capecitabine and its metabolites has been investigated extensively over the past years. This paper reviews methods for the bioanalysis of capecitabine and its metabolites. The focus of this review will be on sample pre-treatment, chromatography and detection. Furthermore, the choice of standards and analytical problems encountered during analysis of capecitabine and its metabolites in biological matrices will be discussed. The major challenges in the bioanalysis of capecitabine and its metabolites are the simultaneous extraction and analysis due to the differences in polarity of the analytes. Furthermore we evaluate currently described methods for the quantification of capecitabine and its metabolites. Future wishes and perspectives are stated that could serve as an inspiration for further development of assays for the quantification of capecitabine and its metabolites. Show less
Fluoropyrimidines, such as 5-fluorouracil (5-FU) and capecitabine, are among the most frequently prescribed anticancer drugs. They are inactivated by the enzyme dihydropyrimidine dehydrogenase (DPD... Show moreFluoropyrimidines, such as 5-fluorouracil (5-FU) and capecitabine, are among the most frequently prescribed anticancer drugs. They are inactivated by the enzyme dihydropyrimidine dehydrogenase (DPD). Up to 5% of the population is DPD deficient and these patients have a significantly increased risk of severe and potentially lethal toxicity when treated with regular doses of 5-FU or capecitabine. DPD is encoded by the gene DPYD and variants in DPYD can lead to a decreased DPD activity. Although prospective DPYD genotyping is a valuable tool to identify patients with DPD deficiency, and thus those at risk for severe and potential life-threatening toxicity, prospective genotyping has not yet been implemented in daily clinical care.With this thesis we improved knowledge on different aspects of DPYD genotyping and DPD phenotyping, in order to better predict DPD deficient patients and personalize their therapy. In addition, we improved clinical implementation of DPYD genotyping, and reduced the risk of severe fluoropyrimidine-induced toxicity in DPYD variant allele carriers. Show less
