A short overview on mycophenolic acid pharmacology and pharmacokinetics.

Immunosuppressive therapy is used in solid organ transplant treatment, and mycophenolic acid (MPA) is one of the immunosuppressive drugs most used worldwide. It is a potent, selective, non-competitive, and reversible inosine monophosphate dehydrogenase (IMPDH) inhibitor that acts to inhibit guanine synthesis. To improve solubility, MPA is used as the prodrug mycophenolate mofetil (MMF) or as an enteric-coated mycophenolate sodium salt (EC-MPS). It is metabolized into mycophenolic acid phenyl glucuronide (MPAG), the inactive and major metabolite, and into acyl glucuronide (AcMPAG), pharmacologically active. In kidney transplantation, combined immunosuppressive therapy with cyclosporine (CsA) and tacrolimus (Tac) is widely used, showing beneficial effects. This paper aimed to review papers published in the last two decades and discuss factors that can interfere with the pharmacokinetics of MPA. Data collected confirm that MPA plasma levels should be monitored to evaluate immunosuppressive therapy since pharmacokinetics can be influenced by factors such as interpatient variability, coadministration of other immunosuppressive agents, post-transplant period, renal function, and dose. However, to perform drug monitoring, costs and facility may be limitations. Monitoring MPAG together with MPA would be a great improvement in therapy as it represents a big part of MPA levels and can be related to the increase of adverse effects.

Comparison of plasma and oral fluid concentrations of mycophenolic acid and its glucuronide metabolite by LC-MS in kidney transplant patients.

PURPOSE: Mycophenolic acid is one of the most used immunosuppressive drugs in solid organ transplant treatments in the world. Developing a highly sensitive analytical method to analyse the drug and its metabolites in oral fluid and plasma is important to evaluate the possibility of using oral fluid as a biological matrix in therapeutic drug monitoring, instead of plasma. METHOD: The liquid chromatography coupled to mass spectrometry (LC-MS) method was developed and validated for determining mycophenolic acid (MPA) and its glucuronide metabolite (MPAG) in oral fluid and plasma, with both matrices presenting a detection limit of 1 ng/mL for MPA and 5 ng/mL for MPAG. Both analytes were analysed after a simple protein precipitation procedure. Transplanted-kidney samples of oral fluid and blood were collected from 13 patients that were hospitalised and kept at - 80 °C until analyses. RESULTS: The proposed method was linear in the concentration range of 5-500 ng/mL for MPA and 10-500 ng/mL for MPAG, with correlation coefficients (r) between 0.9925 and 0.9973. It was then applied to samples collected from kidney-transplanted patients and used for calculation of pharmacokinetics parameters. CONCLUSION: After comparing plasma and oral fluid concentrations as well as performing a non-compartmental pharmacokinetic analysis of the average curves, it is possible to suggest that oral fluid concentration may be used as an alternative for MPA and MPAG monitoring in kidney transplant patients.

Analysis of cocaine/crack biomarkers in meconium by LC-MS.

Fetal exposure to illicit drugs is a worldwide problem, since many addicted women do not stop using it during pregnancy. Cocaine consumed in powdered (snorted or injected) or smoked (crack cocaine) form are harmful for the baby and its side effects are not completely known. Meconium, the first stool of a newborn, is a precious matrix usually discarded, that may contain amounts of substances consumed in the last two trimesters of pregnancy. Analyzing this biological matrix it is possible to detect the unaltered molecule of cocaine (COC) or its metabolite benzoylecgonine (BZE) and pyrolytic products anhydroecgonine methyl ester (AEME) and anhydroecgonine (AEC). A liquid chromatography mass spectrometry (LC-MS) method was validated for meconium samples after solvent extraction, followed by direct injection of 10µL. Linearity covered a concentration range of 15 to 500ng/mg with a lower limit of quantification (LLOQ) of 15ng/mg for all analytes. Matrix effect was evaluated and showed adequate results. Detection of illicit substances usage can be crucial for the baby, since knowing that can help provide medical care as fast as possible. The method proved to be simple and fast, and was applied to 17 real meconium samples.