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Summary Objective: To develop a simple analytical method for monitoring serum and urine concentrations of mycophenolic acid (MPA), an active metabolic constituent of the immunosuppressive pro-drug mycophenolate mofetil, and its glucuronide. Methods: Serum samples were prepared by solid-phase extraction (SPE), while urine samples were simply diluted with water. Serum was added to an SPE cartridge, then washed twice with 5% methanol solution. The analytes were eluted with methanol containing benzoic acid as internal standard for mycophenolic acid glucuronide (MPAG). The resultant eluate was directly injected into a high-performance liquid chromatograph (HPLC) to determine MPAG. For the assay of MPA, the remaining eluate was dried under nitrogen and resolved in a mixture of acetonitrile and 20 mm phosphate buffer (pH 3&bdot;0). Results: The present methods were reproducible and accurate based on the intra- and inter-assay, and had detection limits of 0&bdot;225 μg/mL for MPA and 9&bdot;0 μg/mL for MPAG. The present methods enabled us to monitor the time course of changes in the concentrations of MPA and MPAG in serum and urine in a patient with a renal transplant during 12 h after ingestion of mycophenolate mofetil. Conclusion: The HPLC method described should be useful for the routine monitoring of serum and urine concentrations of MPA and MPAG during immunosuppressive medication for renal transplantation. [ABSTRACT FROM AUTHOR]

A column-switching high-performance liquid chromatographic analysis was established to monitor the serum concentration of mycophenolic acid, the active metabolite from mycophenolate mofetil administered for the prophylaxis of acute organ rejection in renal transplantation. The system consisted of two pumps for solvent delivery, a column-switching valve, a precolumn, and a reversed-phase analytical column. The present method enabled us to determine MPA by injecting serum samples directly into HPLC without any pretreatment. The mobile phases with different amounts of organic solvent were delivered to the precolumn and analytical column by separate lines, and samples were applied to the precolumn. The column switching valves were switched automatically following the processes for the elimination of protein and the drug analysis. The peak heights of MPA were linearly related to the concentrations (r=0.999) in the range of 0.1–20 μg/ml, and the limit of quantification was 0.1 μg/ml (S/N ratio=3). This method was accurate and reproducible on the basis of the results of recovery (94.0–98.0%) and small coefficient of variations of intra and inter-assay (less than 8.3%). [ABSTRACT FROM AUTHOR]