Quantification of mycophenolic acid in human plasma by liquid chromatography with time-of-flight mass spectrometry for therapeutic drug monitoring

This study presents, for the first time, the development and validation of a liquid chromatography and time-of-flight mass-spectrometry (LC-TOF-MS) based assay to quantify mycophenolic acid (MPA) in patient samples as part of a routine therapeutic drug monitoring service. MPA was extracted from 50 mu l human plasma by protein precipitation, using sulindac as internal standard (IS). Separation was obtained on a Luna (TM) Omega polar C-18 column kept at 40 degrees C. The mobile phase consisted of a mixture of acetonitrile-deionized water (50:50, v/v) with 0.1% formic acid at a flow rate of 350 mu l/min. Analyte and IS were monitored on a TOF-MS using a Jet-Stream (TM) (electrospray) interface running in positive mode. Assay performance was evaluated by analysing patient plasma (N = 69) and external quality assessment (N = 6) samples. The retention times were 2.66 and 2.18 min for MPA and IS, respectively. The lower limit of quantification of MPA was 0.1 mu g/ml. The within- and between-assay reproducibility results ranged from 1.81 to 10.72%. Patient and external quality assessment sample results were comparable with those obtained previously by an in-house validated LC-MS/MS method. This method showed satisfactory analytical performance for the determination of MPA in plasma over the calibration range of 0.1-15.0 mu g/ml.