title: HPLC-MS/MS method for the determination of cytarabine in human plasma.
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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: PRA International Early Development Services, Assen, The Netherlands. hilhorstmartijn@praintl.com
authors.forename: Martijn J
authors.initials: MJ
authors.lastname: Hilhorst
authors.forename: Gert
authors.initials: G
authors.lastname: Hendriks
authors.forename: Mischa W J
authors.initials: MW
authors.lastname: van Hout
authors.forename: Henrik
authors.initials: H
authors.lastname: Sillén
authors.forename: Nico C
authors.initials: NC
authors.lastname: van de Merbel
mesh_terms: D000964:Antimetabolites, Antineoplastic / Q000097:blood* / Q000493:pharmacokinetics; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D002853:Chromatography, Liquid / Q000379:methods*; D003561:Cytarabine / Q000097:blood* / Q000493:pharmacokinetics; D004355:Drug Stability; D006801:Humans; D012680:Sensitivity and Specificity; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D000964:Antimetabolites, Antineoplastic; D003561:Cytarabine