Objectives: Mycophenolic acid (MPA), the active metabolite of the ester prodrug mycophenolate mofetil is an immunosuppressant which selectively inhibits inosine-monophosphate dehydrogenase. The requirement for therapeutic drug monitoring shown in previous studies raises the necessity of acquiring accurate and sensitive methods to measure MPA and also its metabolite mycophenolic acid glucuronide (MPAG).
Design and methods: We developed a robust, rapid, sensitive and highly specific HPLC-electrospray ionization mass spectrometry method to assay MPA and its metabolite MPAG in human plasma and serum. Ion suppression was investigated by a post column infusion experiment.
Results: Determination of MPA and MPAG were performed during a 3.0-min run time. Multiple calibration curves for the analysis of MPA and MPAG exhibited consistent linearity and reproducibility in the range of 0.05 to 100 mg/L (r>0.999) and 6 to 400 mg/L r>0.998, respectively. Limits of detection were 0.009 mg/L for MPA and 4.5 mg/L for MPAG and lower limits of quantification were 0.011 mg/L for MPA and 4.9 mg/L for MPAG. Interassay imprecision was <6.0% for both substances. Mean recovery was 48.9% (range 43.3-60.0%) for MPA and 112.2% (range 95.0-127.0%) for MPAG. Agreement was relatively good for MPA (n=122) between the presented method and a validated ELISA method (Viva analyzer, Siemens Medicals Solutions Diagnostics, NY). The Passing-Bablok regression line was: EMIT=0.91 (LC-MS/MS)+0.17 [mg/L]; r=0.97.
Conclusions: This simple, robust and interference-free LC-MS/MS assay allows the rapid and accurate determination of MPA and MPAG in human plasma and other body fluids.