Determination of Endogenous Concentrations of Uracil and Dihydrouracil in Dried Saliva Spots by LC-MS/MS: Method Development, Validation, and Clinical Application.

Background: The aim of this study was to develop and validate a liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for the measurement of uracil (U) and dihydrouracil (UH2) concentrations in dried saliva spots (DSSs), for the evaluation of dihydropyrimidine dehydrogenase (DPD) enzyme activity.

Results: Nine 18-mm diameter DSS discs were extracted with acetate:isopropyl alcohol (85:15, vol/vol) and analyzed by LC-MS/MS. The assay was linear in the range of 10-1000 ng·mL, with accuracy between 89% and 112% and precision between 5.

DPD functional tests in plasma, fresh saliva and dried saliva samples as predictors of 5-fluorouracil exposure and occurrence of drug-related severe toxicity.

Objective: to evaluate plasma and salivary uracil (U) to dihydrouracil (UH2) ratios as tools for predicting 5-fluorouracil systemic exposure and drug-related severe toxicity, and clinically validate the use of dried saliva spots (DSS) as an alternative sampling strategy for dihydropyrimidine dehydrogenase (DPD) deficiency assessment.

Methods: Pre-chemotherapy plasma, fresh saliva and DSS samples were obtained from gastrointestinal patients (N = 40) for measurement of endogenous U and UH2 concentrations by LC-MS/MS. A second plasma sample collected during 5FU infusion was used for 5FU area under the curve (AUC) determination by HPLC-DAD.

Analytical and clinical validation of a dried blood spot assay for the determination of paclitaxel using high-performance liquid chromatography-tandem mass spectrometry.

Background: Paclitaxel (PCT) is a chemotherapeutic drug widely used for the treatment of several types of tumors, and its use is associated with severe adverse events, mainly neurologic and hematopoietic toxicities. The relation between systemic exposure and clinical response to PCT was previously described, making paclitaxel a potential candidate for therapeutic drug monitoring (TDM). The use of dried blood spot (DBS) sampling could allow complex sampling schedules required for TDM of PCT.

Pharmacogenetic and Pharmacokinetic Dose Individualization of the Taxane Chemotherapeutic Drugs Paclitaxel and Docetaxel.

Background: The taxane drugs paclitaxel and docetaxel, widely used on cancer chemotherapy, are currently dosed mainly based on body-surface area. This approach is associated with wide interindividual variability in drug exposure, leading to suboptimal dosing for many patients.

Methods: The available evidence supporting dose individualization strategies for paclitaxel and docetaxel were reviewed, focusing mainly on the application of therapeutic drug monitoring by a priori pharmacogenetic data or a posteriori drug measurements in biological fluids.

Endogenous plasma and salivary uracil to dihydrouracil ratios and DPYD genotyping as predictors of severe fluoropyrimidine toxicity in patients with gastrointestinal malignancies.

Objective: The aim of this study was to evaluate the use of plasma and saliva uracil (U) to dihydrouracil (UH) metabolic ratio and DPYD genotyping, as a means to identify patients with dihydropyrimidine dehydrogenase (DPD) deficiency and fluoropyrimidine toxicity.

Methods: Paired plasma and saliva samples were obtained from 60 patients with gastrointestinal cancer, before fluoropyrimidine treatment. U and UH concentrations were measured by LC-MS/MS.

DBS sampling in imatinib therapeutic drug monitoring: from method development to clinical application.

Background: Imatinib (IM) is widely used in treatment of chronic myeloid leukemia with target trough plasma concentrations above 1000 ng ml(-1). DBS can increase access to IM therapeutic drug monitoring.

Results: IM was measured in the range 50-4000 ng ml(-1) by UHPLC-MS/MS using one 6 mm DBS in a fully validated method.

CYP3A4*22 is related to increased plasma levels of 4-hydroxytamoxifen and partially compensates for reduced CYP2D6 activation of tamoxifen.

Aim: To evaluate the impact of CYP3A4*22 in the formation of endoxifen (EDF) and hydroxytamoxifen (HTF), under different CYP2D6 genotypic backgrounds.

Materials & Methods: 178 patients were enrolled in the study. CYP2D6 and CYP3A4 genotyping and tamoxifen (TAM) and metabolites quantification were performed.

Influence of CYP2D6 and CYP3A4 Phenotypes, Drug Interactions, and Vitamin D Status on Tamoxifen Biotransformation.

Objective: In view of the large variability on therapeutic response and the multiple factors associated to tamoxifen (TAM) metabolic activation, this study aimed to evaluate the effect of CYP2D6 and CYP3A4 phenotypes, drug interactions, and vitamin D exposure on TAM metabolism in a group of breast cancer patients.

Methods: Trough blood samples were collected from 116 patients. TAM and metabolites endoxifen (EDF), N-desmethyltamoxifen, and 4-hydroxytamoxifen (HTF) were measured in plasma by liquid chromatography-tandem mass spectrometry.

Development, validation and clinical application of a HPLC-FL method for CYP2D6 phenotyping in South Brazilian breast cancer patients.

Objective: To develop and validate a method for determination of dextromethorphan (DMT) and dextrorphan (DTP) in plasma samples using HPLC-FL and to apply it to CYP2D6 phenotyping of a population from the South of Brazil.

Methods: Samples were prepared by hydrolysis and liquid-liquid extraction. Analysis was conducted in a reversed phase column, with isocratic elution and fluorescence detection.