Development of a liquid chromatography-tandem mass spectrometric method for quantification of mycophenolic acid and its glucuronides in dried blood spot samples

Background: Personalized immunosuppressive therapy, including accurate drug dosing based on the drug blood level, leads to better clinical outcomes, specifically regarding avoidance of drug-induced adverse effects and maintenance of efficacy. Mycophenolic acid (MPA) is used as an immunosuppressant in transplantation of various solid organs. The aim of this study was to develop a method for quantification of MPA and its metabolites, mycophenolic acid 7-O-glucuronide (MPAG) and mycophenolic acid acyl glucuronide, in dried blood spot (DBS) samples, using liquid chromatography/electrospray ionization/tandem mass spectrometry. Methods: For sample preparation, a microwave-drying approach was used to deactivate enzymes and reduce drying time. Blood volume was calculated in a DBS disk of 3 mm diameter. Concentrations of analytes in plasma from patients receiving mycophenolate mofetil were compared with DBS samples after hematocrit correction. Results: The method yielded good recoveries of all 3 analytes (90.3%-104.2%). Blood volume in the disk was calculated as 3.0 ± 0.2 mL. Linearity over concentration ranges of 0.1-30 mcg/mL MPA, 0.1-200 mcg/mL MPAG, and 0.125-10 mcg/mL mycophenolic acid acyl glucuronide was obtained with r² ≥0.999. Intraday and interday variations were less than 14.6%, and accuracy was within 611.9%. Passing-Bablok analysis showed no significant differences between plasma concentrations and DBS concentrations after hematocrit correction of MPA and MPAG. Conclusions: We developed and validated a liquid chromatography/electrospray ionization-tandem mass spectrometry method for analysis of MPA in DBS samples. The method is useful for monitoring the MPA blood level.