title: A simplified method for busulfan monitoring using dried blood spot in combination with liquid chromatography/tandem mass spectrometry.
abstract: BACKGROUND
  Busulfan (Bu) is an important component of the myeloablative conditioning regimen prior to hematopoietic stem cell transplantation (HSCT) especially in children. Intravenously administered Bu exhibits a therapeutic window phenomenon requiring therapeutic drug monitoring. Analytical methods developed for Bu routine monitoring were aimed at using low volumes of biological fluids and development of simple procedures to facilitate the dosage adjustment. In this report, we describe a simple, rapid method for Bu measurement using dried blood spots (DBS) from only 5 μL of whole blood.
  
  
  METHODS
  Bu extracted from DBS with methanol was measured by high-performance liquid chromatography with electrospray ionization and tandem mass spectrometry in multiple reaction monitoring mode using D8-Bu as an internal standard. The method was in-house validated evaluating trueness, repeatability, within-laboratory reproducibility, specificity and the lower limit of quantification (LLOQ).
  
  
  RESULTS
  The method was linear in the calibration range of 100-2000 ng mL(-1) (r(2)>0.99) encompassing the therapeutic concentrations of Bu. A good trueness (<14%), precision (<10%), and recovery (100%) were observed during validation of the method with quality controls of 300, 600 and 1400 ng mL(-1). The LLOQ was determined as 50 ng mL(-1) and no matrix or carryover effects were observed. The validated method was applied to measure Bu levels in four children receiving infusion of Bu prior to HSCT. A good correlation was observed between the Bu levels measured by DBS and dried plasma spot (DPS) (r(2) =0.96) and between DPS and the GC/MS method (r(2) =0.92). Bu was found to be stable in DBS up to 6 h at room temperature and for 24 h at 4 °C.
  
  
  CONCLUSIONS
  The new DBS method facilitates earlier dosage adjustment during Bu therapy by its specific and simple procedure using 5 μL of whole blood.
authors.affiliation: Department of Pediatrics, Onco-hematology Unit, Geneva University Hospitals, Geneva, Switzerland.
authors.forename: Marc
authors.initials: M
authors.lastname: Ansari
authors.forename: Chakradhara Rao S
authors.initials: CR
authors.lastname: Uppugunduri
authors.forename: Julien
authors.initials: J
authors.lastname: Déglon
authors.forename: Yves
authors.initials: Y
authors.lastname: Théorêt
authors.forename: François
authors.initials: F
authors.lastname: Versace
authors.forename: Fabienne
authors.initials: F
authors.lastname: Gumy-Pause
authors.forename: Hulya
authors.initials: H
authors.lastname: Ozsahin
authors.forename: Pierre
authors.initials: P
authors.lastname: Dayer
authors.forename: Jules
authors.initials: J
authors.lastname: Desmules
authors.forename: Youssef
authors.initials: Y
authors.lastname: Daali
mesh_terms: D002066:Busulfan / Q000097:blood* / Q000493:pharmacokinetics; D002138:Calibration; D002648:Child; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D059788:Dried Blood Spot Testing / Q000379:methods*; D004355:Drug Stability; D006801:Humans; D016014:Linear Models; D015203:Reproducibility of Results; D021241:Spectrometry, Mass, Electrospray Ionization; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D002066:Busulfan