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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]

Objectives: The aim of this study was to identify a target range for inosin-5′-monophosphate dehydrogenase (IMPDH) activity in maintenance therapy with tacrolimus (TCL), and to apply the measurement of IMPDH activity to the therapeutic drug monitoring for mycophenolate mofetil (MMF). Methods: Eleven patients with renal transplants and 10 healthy volunteers were investigated. All patients were treated with a combination of TCL, steroid and MMF for 2 months after transplantation, and were in stable and good condition. IMPDH activity was determined indirectly by measuring xanthosine 5′-monophophate in cell lysates supplemented with IMP and β-nicotine adenine dinucleotide using an high-performance liquid chromatography (HPLC) method. Results: The within-run reproducibility of the assay was excellent, with relative standard deviation (RSD) values of 0·41–4·08%. The mean differences between the spiked concentrations of xanthosine 5′-monophophate and their real values (mean relative errors; MREs) were within a range of 2·66–8·89%, showing good accuracy. The interday RSD values were 1·51–6·12% and MREs ranged from 2·10% to 8·89%. Cell lysates showed a 5–6 nmol/L IC50 mycophenolic acid (MPA) concentration. TCL, cyclosporine and prednisolone did not affect IMPDH activity. The peak MPA concentration was achieved at 1 h after dosing. IMPDH activity decreased to 75% and 67% at 1 and 2 h after dosing respectively. Therefore, the inhibition rates of MPA against IMPDH activity may be adequate at 25–40% in TCL maintenance therapy. Conclusion: Inosin-5′-monophosphate dehydrogenase activity in cell lysates could be reliably determined by HPLC. A 25–40% inhibition of IMPDH activity may be an appropriate range for preventing rejection with MPF but this requires further validation using larger studies with harder outcomes such as rejection episodes. [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]

Objectives: The aim of this study was to develop a limited sampling strategy (LSS) for monitoring the use of mycophenolic acid (MPA) in maintenance therapy with tacrolimus (TCL) in renal transplant patients. Methods: Eighteen adult patients receiving a first transplant were investigated. All patients were treated with a combination of TCL, steroid and mycophenolate mofetil (MMF). Besides the predose trough concentration ( C0), whole blood samples were taken for measurement of the MPA concentration at 0·5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12 h for a 14-point 12-h pharmacokinetic (PK) profile. Using stepwise linear regression analysis, an abbreviated area under the concentration time curve (AUC) was calculated using all 14, and any combination of sampling points to give an estimating equation with up to three predictors. Results: The equation derived from C2, C7 and C12, for AUC estimation: AUC = (2·05 × C2) + (8·51 × C7) + (2·29 × C12) + 4·24. was found to be optimal. Using this formula, there was an excellent correlation between the estimated 3-point AUC and AUC0–12 h. To assess the agreement between the abbreviated methods and the full PK profile, we plotted the average AUC of the abbreviated estimates and the full PK profile. This Bland-Altman analysis indicated good agreement to within ±2 SD and a prediction variability of 7·56 μg × h/mL. Conclusion: Our proposed three-sampling-point estimate of AUCs is clinically acceptable. However, the sampling times are inconvenient for outpatients, and is recommended only for monitoring MMF treatment of inpatients with suspected toxicity or at high risk of organ rejection. [ABSTRACT FROM AUTHOR]