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 μl human plasma by protein precipitation, using sulindac as internal standard (IS). Separation was obtained on a Luna™ Omega polar C 18 column kept at 40°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 μl/min. Analyte and IS were monitored on a TOF–MS using a Jet‐Stream™ (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 μg/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 μg/ml.