A Simple and Accurate Liquid Chromatography-Tandem Mass Spectrometry Method for Therapeutic Drug Monitoring of Busulfan in Plasma

Objective. Busulfan, frequently used as a conditioning regimen for hematopoietic stem cell transplantation, has a narrow therapeutic range and wide intra- and interpatient variabilities. Therefore, therapeutic drug monitoring of busulfan is necessary to ensure that the drug concentrations of patients are within a targeted therapeutic range. In this study, we developed a simple and accurate method for measuring busulfan concentrations using liquid chromatography tandem mass spectrometry (LC-MS/MS). Methods. Separation and detection of busulfan was performed using T3 column equipped with LC-MS/MS. Busulfan was isolated from 50 mu L human plasma after mixing with busulfan(-2)H(8) (internal standard) solution, calibrator, and quality-control material. The sample was eluted and gradated with a mobile phase composed of ammonium acetate, formic acid, and water or methanol. The busulfan concentration was quantified using a six-point standard curve. Busulfan and busulfan(-2)H(8) were detected in positive-ion multiple-reaction-monitoring mode. According to the Clinical and Laboratory Standards Institute guideline, we verified the precision, linearity, limit of detection (LOD), limit of quantification (LOQ), and carryover. Results. Busulfan and busulfan(-2)H(8) were detected at m/z 264.1>151.1 and 272.2>159.1. The total run time was 3 min. Both intra-and inter-assay coefficients of variation were <3%. The calibration curve was linear at 25-5,000 ng/mL. The LOD and LOQ were 2.5 ng/mL and 25 ng/mL, respectively. The recoveries ranged from 92.0-104.8% and the carryover was -0.02%. Conclusions. Our method for busulfan reduces total run time and has excellent analytical performance. It will be a useful method for therapeutic drug monitoring of busulfan in clinical laboratories.