Determination of Treosulfan and Fludarabine in Plasma by Turbulent Flow Liquid Chromatography-Tandem Mass Spectrometry (TFLC-MS/MS).

Treosulfan is a structural analog of the alkylating agent busulfan which has been shown in clinical trials to exhibit comparable myeloablative activity while causing fewer serious side effects. Treosulfan is currently being considered for FDA approval in combination with fludarabine, one of the most commonly used myeloablative agents, as a conditioning regimen prior to hematopoietic stem cell transplantation (HSCT). Because plasma concentrations of both treosulfan and fludarabine exhibit significant interindividual variability, therapeutic drug monitoring (TDM) is indicated to ensure dosages are administered that maximize efficacy while minimizing toxicity. In this chapter, we describe a rapid, accurate assay to detect treosulfan and fludarabine simultaneously in human plasma using turbulent flow liquid chromatography coupled to electrospray ionization tandem mass spectrometry (TFLC-ESI-MS/MS). Treosulfan and fludarabine are extracted from only 100 μL of acidified plasma via protein precipitation with methanol containing isotope-labeled internal standards. The extract is injected into the TFLC-ESI-MS/MS system, and the analytes are quantified using multiple reaction monitoring and a six-point calibration curve.