Monitoring of N,N-dimethylacetamide in children during i.v.-busulfan therapy by liquid chromatography–mass spectrometry

Recently, an intravenous (i.v.) formulation of busulfan using the potentially hepatotoxic and neurotoxic N,N-dimethylacetamide (DMA) as a solvent was introduced. There is a need to assess the exposure of DMA in patients during the intravenous high dose therapy. A rapid and selective LC–MS method was developed to quantify relevant DMA concentration in plasma. After protein precipitation with trichloroacetic acid, the isocratic separation was achieved using a 150 mm × 2 mm C18 column and elution with a mobile phase containing 0.1% formic acid in water/acetonitrile (97:3). Detection of DMA was carried out with a ThermoFinnigan single-quadrupole mass spectrometer in selected-ion monitoring mode as H+-adduct at m/z 88.2. Deuterium-labelled DMA was used as the internal standard. The LC–MS method was accurate, precise and reproducible in the range from 0.25 to 150 mg/l and met the generally accepted criteria for bioanalytical methods. Two calibration ranges from 0.25 to 7.5 mg/l and 7.5 to 150 mg/l were used. The intra- (n = 7) and interassay (n = 7) accuracy and precision were both <7.7% and the limit of quantification is 0.25 mg/l. The method was successfully applied to investigate 203 plasma samples in children during the i.v.-busulfan therapy.