Analysis of mycophenolic acid in saliva using liquid chromatography tandem mass spectrometry

Salivary levels of the immunosuppressive agent, mycophenolic acid (MPA), may provide a convenient and noninvasive method for drug monitoring. An analytical method was developed and validated for quantification of salivary MPA using liquid chromatography tandem mass spectrometry. Sample preparation included addition of 50 mu L internal standard solution [500 mu g/L indomethacin in methanol] to 100 mu L saliva sample, followed by protein precipitation with 200 mu L acetonitrile. Supernatants were dried and reconstituted in 100 mu L of 85:15% (vol/vol) mixture of methanol and water containing 0.05% formic acid and 20 mu L was injected onto the analytical column. The mobile phase comprised a gradient mixture of methanol and 0.05% formic acid, giving a total run time of 7.5 minutes. Chromatograms were obtained using mass transitions of m/z 319.0 -> 190.8 for MPA and m/z 355.9 -> 312.2 for indomethacin. The calibration curve was linear over a concentration range of 2.5 to 800 mu g/L (r = 0.9999) and the recovery of MPA from saliva was > 90%. The inaccuracy was < 10% and intra- and interday coefficient of variation ranged from 2.8% to 5.2%. Mean +/- SD of MPA concentrations in saliva (n = 100) obtained from 11 kidney transplant recipients was 31.4 +/- 32.3 mu g/L (range: 2.6 to 220.4 mu g/L) and correlated well with total (r = 0.909) and unbound (r = 0.910) MPA concentrations in plasma. In conclusion, a simple, sensitive, and specific method was developed and validated for quantification of MPA in saliva. Additional clinical studies are required to establish the usefulness of this specimen in the clinical management of organ transplant recipients.