Background: High-dose Busulfan is widely used in conditioning regimens before hematopoietic stem cell transplantation in both adults and children. Large inter-individual variability in ...pharmacokinetics after oral administration has been reported; therefore, therapeutic drug monitoring of Busulfan may decrease the incidence of drug-related toxicity (for example, hepatic venoocclusive disease) and may also improve therapeutic efficacy. Methods: Busulfan concentrations were quantified using 200 microL of plasma and liquid-liquid extraction with diethyl ether after the addition of sup.2H.sub.8Busulfan as the internal standard. Separation and detection of Busulfan and sup.2H.sub.8Busulfan were achieved with a LUNA CS column (5 microm; 150 x 2 mm i.d.) at 30 degreesC, a HP 1100 liquid chromatography system, and a HP 1100 single-quadrupole mass spectrometer. Busulfan and sup.2H.sub.8Busulfan were detected as ammonium adducts in selected-ion monitoring mode at m/z 264.2 and 272.2, respectively. Results: The calibration curve was linear at 5-2000 microg/L Busulfan. Intra- and interassay imprecision (CV) and bias were both <11%. The limits of detection and quantification were 2 and 5 microg/L, respectively. Extraction recovery of Busulfan was >87%. Analysis of pharmacokinetics in four patients receiving high-dose Busulfan indicated that minimum Busulfan concentrations before the next dose were 405-603 microg/L, with no interference observed. Conclusions: The new rapid and sensitive liquid chromatographic-mass spectrometric assay is an appropriate method for quantification of Busulfan in human plasma, making therapeutic drug monitoring of Busulfan faster and easier in clinical practice.
