ABSTRACT
BACKGROUND: Cytarabine is an anti-tumor drug that is currently under investigation for treatment in combination with other anticancer drugs for the chemotherapy of leukemia. The quantitative determination of cytarabine in plasma is challenging due to the required sensitivity, its in vitro instability and the presence of an isobaric endogenous compound, cytidine. Owing to the polarity of cytarabine, conventional chromatography cannot provide adequate separation of the analyte and the interfering compounds. A few analytical methods have been reported for the determination of cytarabine in plasma, but their sensitivity was not sufficient since most of these methods apply spectrophotometric detection. RESULTS: In this article, an LC-MS/MS method is described for the determination of cytarabine in human plasma down to the sub ng/ml level. To prevent conversion of cytarabine by cytidine deaminase, whole blood samples were stabilized with tetrahydrouridine directly after the collection of whole blood at the clinical site. Cation-exchange SPE was employed to extract cytarabine from 50 µl human plasma. UHPLC on high strength silica T3 column (100 × 2.1 mm × 1.8 µm) was applied to achieve adequate separation of cytarabine from cytidine within a reasonable run time of 5 min. A triple quad mass spectrometer equipped with an ESI source was used for detection. CONCLUSION: The method was linear over the concentration ranges of 0.500-500 ng/ml. The intra- and inter-day relative standard deviation (precision) as well as the bias (accuracy) were well below 15%. In the presence of tetrahydrouridine, cytarabine was sufficiently stable under all relevant conditions. The method was successfully applied to support a clinical pharmacokinetic study with a low dose of cytarabine.
Subject(s)
Antimetabolites, Antineoplastic/blood , Chromatography, High Pressure Liquid/methods , Chromatography, Liquid/methods , Cytarabine/blood , Tandem Mass Spectrometry/methods , Antimetabolites, Antineoplastic/pharmacokinetics , Cytarabine/pharmacokinetics , Drug Stability , Humans , Sensitivity and SpecificityABSTRACT
A novel liquid chromatography-tandem mass spectrometry method is described for the quantitative determination of the endogenous CYP 3A4/5 marker 4ß-hydroxycholesterol in human K(2)-EDTA plasma. It is based on alkaline hydrolysis to convert esterified to free 4ß-hydroxycholesterol, followed by analyte extraction from plasma by hexane and purification of the hexane extract by normal-phase solid-phase extraction. The analyte is chromatographically separated from endogenous isobaric plasma oxysterols and excess cholesterol by a 16-min reversed-phase gradient on a C18 column; detection is performed by atmospheric pressure photoionization tandem mass spectrometry in the positive ion mode, using toluene as a dopant. Using 400µl of plasma, 4ß-hydroxycholesterol can be quantified in the concentration range 10.0-250nM. Validation results show that the method is sufficiently selective towards endogenous plasma sterols and capable of quantifying the analyte with good precision and accuracy. The analyte is sufficiently stable in all relevant matrices and solvents; the addition of the anti-oxidant butylated hydroxytoluene to prevent in vitro formation of 4ß-hydroxycholesterol from cholesterol during storage or analysis is not necessary, provided that long-term frozen storage of plasma occurs at -70°C.