Within-Patient Variability of Mycophenolic Acid Exposure

Population pharmacokinetics of mycophenolic acid and dose optimisation in adult Chinese kidney transplant recipients

1. This study aimed to establish a population pharmacokinetic (PPK) model of mycophenolic acid (MPA), quantify the effect of clinical factors and pharmacogenomics of MPA, and optimise the dosage for adult kidney transplant recipients.2. One-hundred and four adult renal transplant patients were enrolled. The PPK model was established using the Phoenix® NMLE software and the stepwise methods were filtered for significant covariates. Monte Carlo simulations were performed to optimise the dosage regimen.3. A two-compartment model with first-order absorption and elimination (including lag time) provided a more accurate description of MPA pharmacokinetics. Serum albumin (ALB) significantly affected the central apparent clearance (CL/F), whereas post-transplant time and creatinine clearance were associated with a central apparent volume of distribution (V/F). The estimated population values obtained by the final model were 17.5 L/h and 93.97 L for CL/F and V/F, respectively. Simulation results revealed that larger mycophenolate mofetil doses are required as the ALB concentration decreases. This study established a PPK model of MPA and validated it using various methods. ALB significantly affected CL/F and recommended optimal dose strategies were given based on the final model. These results provide a reference for the personalised therapy of MPA for kidney transplant patients.

Individualization of Mycophenolic Acid Therapy through Pharmacogenetic, Pharmacokinetic and Pharmacodynamic Testing

Mycophenolic acid (MPA) is a widely used immunosuppressive agent and exerts its effect by inhibiting inosine 5′-monophosphate dehydrogenase (IMPDH), the main regulating enzyme of purine metabolism. However, significant unexplained differences in the efficacy and tolerability of MPA therapy pose a clinical challenge. Therefore, broad pharmacogenetic, pharmacokinetic, and pharmacodynamic approaches are needed to individualize MPA therapy. In this prospective cohort study including 277 renal transplant recipients, IMPDH2 rs11706052 SNP status was assessed by genetic sequencing, and plasma MPA trough levels were determined by HPLC and IMPDH enzyme activity in peripheral blood mononuclear cells (PBMCs) by liquid chromatography–mass spectrometry. Among the 277 patients, 84 were identified with episodes of biopsy-proven rejection (BPR). No association was found between rs11706052 SNP status and graft rejection (OR 1.808, and 95% CI, 0.939 to 3.479; p = 0.076). Furthermore, there was no association between MPA plasma levels and BPR (p = 0.69). However, the patients with graft rejection had a significantly higher predose IMPDH activity in PBMCs compared to the controls without rejection at the time of biopsy (110.1 ± 50.2 vs. 95.2 ± 45.4 pmol/h; p = 0.001), and relative to the baseline IMPDH activity before transplantation (p = 0.042). Our results suggest that individualization of MPA therapy, particularly through pharmacodynamic monitoring of IMPDH activity in PBMCs, has the potential to improve the clinical outcomes of transplant patients.

Mycophenolate mofetil, azathioprine and tacrolimus: mechanisms in rheumatology

The introduction of biologic DMARDs into rheumatology has resulted in a substantial reduction of the burden of many rheumatic diseases. In the slipstream of the success achieved with these biologic DMARDs, some conventional immunosuppressive drugs have also found use in new indications. Notably, mycophenolate mofetil, azathioprine and tacrolimus have made their way from solid organ transplantation drugs to become useful assets in rheumatology practice. Mycophenolate mofetil and azathioprine inhibit the purine pathway and subsequently diminish cell proliferation. Both drugs have a pivotal role in the treatment of various rheumatic diseases, including lupus nephritis. Tacrolimus inhibits lymphocyte activation by inhibiting the calcineurin pathway. Mycophenolate mofetil and tacrolimus are, among other indications, increasingly being recognized as useful drugs in the treatment of interstitial lung disease in systemic rheumatic diseases and skin fibrosis in systemic sclerosis. A broad array of trials with mycophenolate mofetil, azathioprine and/or tacrolimus are ongoing within the field of rheumatology that might provide further novel avenues for the use of these drugs. In this Review, we discuss the historical perspective, pharmacodynamics, clinical indications and novel avenues for mycophenolate mofetil, azathioprine and tacrolimus in rheumatology.

Population pharmacokinetics and Bayesian estimation of mycophenolic acid concentrations in Chinese adult renal transplant recipients

Mycophenolate mofetil (MMF) is an important immunosuppressant used in renal transplantation, and mycophenolic acid (MPA) is the active component released from the ester prodrug MMF. The objective of this study was to investigate the population pharmacokinetics of mycophenolic acid (MPA) following oral administration of MMF in Chinese adult renal transplant recipients and to identify factors that explain MPA pharmacokinetic variability. Pharmacokinetic data for MPA and covariate information were retrospectively collected from 118 patients (79 patients were assigned to the group for building the population pharmacokinetic model, while 39 patients were assigned to the validation group). Population pharmacokinetic data analysis was performed using the NONMEM software. The pharmacokinetics of MPA was best described by a two-compartment model with a first-order absorption rate with no lag time. Body weight and serum creatinine level were positively correlated with apparent clearance (CL/F). The polymorphism in uridine diphosphate glucuronosyltransferase gene, UGT2B7, significantly explained the interindividual variability in the initial volume of distribution (V₁/F). The estimated population parameters (and interindividual variability) were CL/F 18.3 L/h (34.2%) and V₁/F 27.9 L (21.3%). The interoccasion variability was 13.7%. These population pharmacokinetic data have significant clinical value for the individualization of MMF therapy in Chinese adult renal transplant patients.

Mycophenolic mofetil optimized pharmacokinetic modelling, and exposure-effect associations in adult heart transplant recipients

Mycophenolic acid (MPA) area under the curve (AUC) has been associated with graft outcome.

THE AIMS OF OUR STUDY WERE

(1) to develop pharmacokinetic tools to optimize MPA inter-dose AUC estimation in heart transplant patients; and (2) to investigate the relationships between acute allograft rejection and MPA AUC, trough level (C0) or mycophenolate mofetil (MMF) dose. Two independent modeling approaches (parametric and non parametric) were used to fit 56 rich MPA pharmacokinetic (PK) profiles collected from 40 adult heart transplant recipients enrolled in the PIGREC study, receiving MMF and a calcineurin inhibitor (CNI), in the first year post-transplantation. In addition, associations between drug exposure (MPA C0, AUC and MMF dose) and acute rejection or MMF adverse events were investigated using time-dependent Cox models with stratification on the type of calcineurin inhibitor. Exposure threshold values were investigated using ROC curve analysis. The 2 models developed fit adequately the data and the use of their combination yielded 100% consistency with the measured AUC in terms of strategy of dose adjustment (maintain, increase or decrease). MPA measured AUC adjusted on CNI exposure was significantly associated with rejection (per unit increase: HR [95% CI]=0.97 [0.95-0.99], p=0.0122), while no effect was shown for adverse events attributable to MMF. An AUC threshold of 50 mg×h/L was proposed (sensitivity=77%, specificity=25%) beyond which the risk of rejection was significantly increased (low vs. high: HR=3.48 [1.21-10.0], p=0.0204). The tools developed have already been made available to the heart transplant community on our ISBA website (https://pharmaco.chu-limoges.fr).

Therapeutic drug monitoring in pediatric renal transplantation

Finding the balance between clinical efficacy and toxicity of immunosuppressive drugs is a challenge in renal transplantation (RTx), but especially in pediatric RTx patients. Due to the expected longer life-span of pediatric transplant patients and the long-term consequences of drug-induced infectious, malignant and cardiovascular adverse effects, protocols which minimize immunosuppressive therapy make conceptual sense. In this context, therapeutic drug monitoring is a tool which provides support for the individualization of therapy. It has, however, limitations, and specific data in the pediatric cohort are comparatively sparse. There is large heterogeneity among the studies conducted to date in terms of methods, follow-up, endpoints, immunosuppressive regimens and patients. In addition, data from adult studies are not readily transferrable to the pediatric situation. This educational review gives a concise overview on aspects of therapeutic drug monitoring in pediatric RTx.

Maximum a posteriori Bayesian estimation of mycophenolic Acid area under the concentration-time curve: is this clinically useful for dosage prediction yet?

This review seeks to summarize the available data about Bayesian estimation of area under the plasma concentration-time curve (AUC) and dosage prediction for mycophenolic acid (MPA) and evaluate whether sufficient evidence is available for routine use of Bayesian dosage prediction in clinical practice. A literature search identified 14 studies that assessed the predictive performance of maximum a posteriori Bayesian estimation of MPA AUC and one report that retrospectively evaluated how closely dosage recommendations based on Bayesian forecasting achieved targeted MPA exposure. Studies to date have mostly been undertaken in renal transplant recipients, with limited investigation in patients treated with MPA for autoimmune disease or haematopoietic stem cell transplantation. All of these studies have involved use of the mycophenolate mofetil (MMF) formulation of MPA, rather than the enteric-coated mycophenolate sodium (EC-MPS) formulation. Bias associated with estimation of MPA AUC using Bayesian forecasting was generally less than 10%. However some difficulties with imprecision was evident, with values ranging from 4% to 34% (based on estimation involving two or more concentration measurements). Evaluation of whether MPA dosing decisions based on Bayesian forecasting (by the free website service https://pharmaco.chu-limoges.fr) achieved target drug exposure has only been undertaken once. When MMF dosage recommendations were applied by clinicians, a higher proportion (72-80%) of subsequent estimated MPA AUC values were within the 30-60 mg · h/L target range, compared with when dosage recommendations were not followed (only 39-57% within target range). Such findings provide evidence that Bayesian dosage prediction is clinically useful for achieving target MPA AUC. This study, however, was retrospective and focussed only on adult renal transplant recipients. Furthermore, in this study, Bayesian-generated AUC estimations and dosage predictions were not compared with a later full measured AUC but rather with a further AUC estimate based on a second Bayesian analysis. This study also provided some evidence that a useful monitoring schedule for MPA AUC following adult renal transplant would be every 2 weeks during the first month post-transplant, every 1-3 months between months 1 and 12, and each year thereafter. It will be interesting to see further validations in different patient groups using the free website service. In summary, the predictive performance of Bayesian estimation of MPA, comparing estimated with measured AUC values, has been reported in several studies. However, the next step of predicting dosages based on these Bayesian-estimated AUCs, and prospectively determining how closely these predicted dosages give drug exposure matching targeted AUCs, remains largely unaddressed. Further prospective studies are required, particularly in non-renal transplant patients and with the EC-MPS formulation. Other important questions remain to be answered, such as: do Bayesian forecasting methods devised to date use the best population pharmacokinetic models or most accurate algorithms; are the methods simple to use for routine clinical practice; do the algorithms actually improve dosage estimations beyond empirical recommendations in all groups that receive MPA therapy; and, importantly, do the dosage predictions, when followed, improve patient health outcomes?

Mycophenolic acid area under the curve recovery time following rifampicin withdrawal

Renal transplant patients prescribed mycophenolate mofetil (MMF) may require treatment for tuberculosis with a regimen including the tuberculocidal drug rifampicin. MMF is an ester prodrug which is rapidly hydrolysed to the active compound, mycophenolic acid (MPA). Therapeutic drug monitoring of mycophenolate involves the measurement of MPA area under the curve (MPA-AUC_0-12). Rifampicin is known to increase the metabolism and decrease enterohepatic recirculation of mycophenolic acid, (MPA). When MPA is monitored after the discontinuation of rifampicin, an important factor is the time required for the MPA area under the curve to return to the pre-rifampicin value. At present this is not known. This report describes one such renal allograft patient, on long term MMF and prescribed rifampicin by a local physician. As expected there was a clinically significant decrease in MPA-AUC_0-12 Three weeks after rifampicin was discontinued the MPA-AUC_0-12 was still only 65% of the pre-rifampicin value and only 55% of the steady state MPA-AUC_0-12 measured six months later.

Efficacy and safety of conversion of mycophenolate mofetil to enteric-coated mycophenolate sodium in Mexican renal transplant children

The aim of the study was to evaluate the efficacy and safety of the conversion of MMF to EC-MPS in pediatric renal transplant recipients. We included 12 patients with stable graft function who were receiving MMF treatment. In the first visit, a complete medical examination was performed, which included a GSRS, a nine-point pharmacokinetic profile, samples for renal, liver and hematological tests and evaluation of IMPDH2 gene expression. The patients were transferred to an equimolar dose of EC-MPS. Two wk later, a clinical evaluation and blood collection, as in the first visit were performed. There was no change in serum creatinine, leukocyte count, serum albumin, or transaminase levels, but we found a statistically significant reduction of hemoglobin after conversion (13.2 +/- 1.6 g/dL with MMF vs. 12.5 +/- 1.3 g/dL when receiving EC-MPS). The GSRS total mean score was 16 +/- 12 with MMF vs. 8 +/- 5 with EC-MPA (p < 0.05). There was no statistically significant difference between formulations in the gene expression of IMPDH 2, in the AUC(0-12h) or in C(max). However, peak concentration occurred later with EC-MPS.

Inosine monophosphate dehydrogenase (IMPDH) activity as a pharmacodynamic biomarker of mycophenolic acid effects in pediatric kidney transplant recipients

Monitoring inosine monophosphate dehydrogenase (IMPDH) activity as a biomarker of mycophenolic acid (MPA)-induced immunosuppression may serve as a novel approach in pharmacokinetics (PK)/pharmacodynamics (PD)-guided therapy. The authors prospectively studied MPA pharmacokinetics and IMPDH inhibition in 28 pediatric de novo kidney transplant recipients. Pretransplant IMPDH activity and full PK/PD profiles were obtained at 3 different occasions: 1 to 3 days, 4 to 9 days, and approximately 6 months after transplant. Large intra- and interpatient variability was noted in MPA pharmacokinetics and exposure and IMPDH inhibition. MPA exposure (AUC(0-12 h)) was low early posttransplant and increased over time and stabilized at months 3 to 6. Mean pretransplant IMPDH activity (6.4 ± 4.6 nmol/h/mg protein) was lower than previously reported in adults. In most of the patients, IMPDH enzyme activity decreased with increasing MPA plasma concentration, with maximum inhibition coinciding with maximum MPA concentration. The overall relationship between MPA concentration and IMPDH activity was described by a direct inhibitory E(max) model (EC(50) = 0.97 mg/L). This study suggests the importance of early PK/PD monitoring to improve drug exposure. Because IMPDH inhibition is well correlated to MPA concentration, pretransplant IMPDH activity may serve as an early marker to guide the initial level of MPA exposure required in a pediatric population.

New insights into the pharmacokinetics and pharmacodynamics of the calcineurin inhibitors and mycophenolic acid: possible consequences for therapeutic drug monitoring in solid organ transplantation

Although therapeutic drug monitoring (TDM) of immunosuppressive drugs has been an integral part of routine clinical practice in solid organ transplantation for many years, ongoing research in the field of immunosuppressive drug metabolism, pharmacokinetics, pharmacogenetics, pharmacodynamics, and clinical TDM keeps yielding new insights that might have future clinical implications. In this review, the authors will highlight some of these new insights for the calcineurin inhibitors (CNIs) cyclosporine and tacrolimus and the antimetabolite mycophenolic acid (MPA) and will discuss the possible consequences. For CNIs, important relevant lessons for TDM can be learned from the results of 2 recently published large CNI minimization trials. Furthermore, because acute rejection and drug-related adverse events do occur despite routine application of CNI TDM, alternative approaches to better predict the dose-concentration-response relationship in the individual patient are being explored. Monitoring of CNI concentrations in lymphocytes and other tissues, determination of CNI metabolites, and CNI pharmacogenetics and pharmacodynamics are in their infancy but have the potential to become useful additions to conventional CNI TDM. Although MPA is usually administered at a fixed dose, there is a rationale for MPA TDM, and this is substantiated by the increasing knowledge of the many nongenetic and genetic factors contributing to the interindividual and intraindividual variability in MPA pharmacokinetics. However, recent, large, randomized clinical trials investigating the clinical utility of MPA TDM have reported conflicting data. Therefore, alternative pharmacokinetic (ie, MPA free fraction and metabolites) and pharmacodynamic approaches to better predict drug efficacy and toxicity are being explored. Finally, for MPA and tacrolimus, novel formulations have become available. For MPA, the differences in pharmacokinetic behavior between the old and the novel formulation will have implications for TDM, whereas for tacrolimus, this probably will not to be the case.

Clinical utility of a new enzymatic assay for determination of mycophenolic acid in comparison with an optimized LC-MS/MS method

The goal of this study was to investigate the clinical utility of a new enzymatic assay for use on COBAS INTEGRA systems (Roche Total MPA assay). From 134 patients, plasma mycophenolic acid (MPA) concentrations were measured with both the enzymatic method and a validated liquid chromatography with tandem mass spectrometry (LC-MS/MS) procedure, to compare these assays. The test principle of the enzymatic assay is inhibition of inosine monophosphate dehydrogenase. Method comparison studies revealed good agreement of results (r > 0.99), overall and in patients with delayed graft function or hypoalbuminemia. MPA area under the concentration-time curve (AUCs) obtained with LC-MS/MS (x) and the enzymatic method (y) compared excellent in patients on cyclosporine (y = 1.04x - 1.05, r = 0.992) or tacrolimus (y = 1.02x - 0.63, r = 0.987). MPA exposure determined with either method at different time points after transplantation agreed well (eg, 25th/50th/75th percentile of day 10 AUCs-LC-MS/MS: 25.8/33.8/45.2 versus enzymatic assay: 26.2/34.4/45.3 mg.h/L). AUCs calculated for both methods were lower at the first 3 time points in patients on cyclosporine compared with tacrolimus (week 4 median cyclosporine/tacrolimus: LC-MS/MS 39.6/56.4 versus enzymatic assay 40.5/56.0 mg.h/L). Both LC-MS/MS and the enzymatic methods revealed a tendency toward lower AUCs and predose levels in patients with biopsy-proven acute rejection (BPAR) (day 10 median: 0.9 mg/L with BPAR and 1.7 mg/L without BPAR). The Roche Total MPA assay is a reliable alternative to LC-MS/MS. It can be applied in the clinical setting allowing for easy, fast, and optimized patient management.

Reduced-intensity conditioning allogeneic transplantation from unrelated donors: evaluation of mycophenolate mofetil plus cyclosporin A as graft-versus-host disease prophylaxis

In the current study, we have analyzed the efficacy of cyclosporine A (CSA) plus mycophenolate mofetil (MMF) as graft-versus-host disease (GVHD) prophylaxis in the fludarabine plus melphalan or busulfan reduced intensity regimen (RIC) setting in a series of 44 patients receiving allogeneic transplantation from an unrelated donor. Only 23% were in the first complete remission at the time of transplant. Cumulative incidence of grades II-IV and III-IV acute GVHD (aGVHD) was 53% and 23%, respectively. Fifty-six percent had equal to or greater than grade 2 gut involvement. Cumulative incidence of overall and extensive chronic GVHD (cGVHD) was 93% and 63%, respectively. Ninety-two percent of patients who were evaluable +100 days after transplant were in complete remission. Relapse rate was 25% at 2 years. Event free (EFS) and overall survival (OS) at 2 years were 52%. Pharmacokinetic assays of mycophenolic acid (MPA) showed a therapeutic area under the curve (AUC) at the dosage of 3 g daily, although a large inter- and intraindividual variations of MPA plasma levels were found. In conclusion, the combination of CSA plus MMF in the fludarabine plus melphalan or busulfan RIC setting is feasible. Regarding GVHD, this combination allowed to control aGVHD but lead to a high incidence of cGVHD, so that newer strategies are required, especially in trying to decrease gastrointestinal involvement.

Evaluation of the practicability of limited sampling strategies for the estimation of mycophenolic acid exposure in Chinese adult renal recipients

The immunosuppressive potential of mycophenolic acid (MPA) correlates well with MPA exposure [area under the concentration-time curve (AUC)]. Monitoring MPA AUC is important and helpful for maintaining the efficacy of mycophenolate mofetil while minimizing its side effects, but full MPA AUC monitoring is laborious, cost prohibitive, and impractical. Limited sampling strategies have been proposed as an alternative method for estimating MPA exposure. The objective of this study was to evaluate the practicability of different limited sampling strategies for the estimation of MPA exposure. A total of 56 pharmacokinetic profiles from 53 adult renal recipients were used to evaluate the practicability of 10 published models. Standard correlation and linear regression analysis were used to compare the estimated MPA AUCs and corresponding full MPA AUCs, and the percentage of profiles for which prediction error fell within +/-20% was also used to assess the practicability of these models. Agreement between the estimated MPA AUCs and full MPA AUCs was further tested by Bland and Altman analysis. The model, based on four sampling time points, used the formula AUC = 12.61 + 0.37 x C0.5 + 0.49 x C1 + 3.22 x C4 + 8.17 x C10, was superior to all other evaluated models, with the highest coefficient of determination (r = 0.88), a low percentage prediction error (2.79%), and good agreement according to Bland and Altman analysis. Prediction errors of 87.5% (49/56) of profiles were within 20%, which was the highest of all the models. This algorithm can be reliably used for estimating MPA exposure in adult renal transplant patients treated with cyclosporine as concomitant immunosuppressant. Another model based on the formula AUC = 8.22 + 3.16 x C0 + 0.99 x C1 + 1.33 x C2 + 4.18 x C4 also has acceptable predictive performance, and it may also be practical, especially in outpatient settings, in view of its distribution of time points.

Sensitive high-performance liquid chromatography–tandem mass spectrometry method for quantitative analysis of mycophenolic acid and its glucuronide metabolites in human plasma and urine

A method to determine total and free mycophenolic acid (MPA) and its metabolites, the phenolic (MPAG) and acyl (AcMPAG) glucuronides, using HPLC and mass spectrometry was developed. Mean recoveries in plasma and urine samples were >85%, and the lower limits of quantification for MPA, MPAG and AcMPAG were 0.05, 0.05 and 0.01 mg/L, respectively. For plasma, the assay was linear over 0.05-50 mg/L for MPA and MPAG, and from 0.01 to 10mg/L for AcMPAG. A validation study demonstrated good inter- and intra-day precision (CV<or=11%) and accuracy (bias<or=16%) and satisfactory specificity and stability. Pharmacokinetic parameters were assessed in plasma and urine from healthy volunteers after an oral dose of mycophenolate mofetil.

Plasma concentrations of mycophenolic acid acyl glucuronide are not associated with diarrhea in renal transplant recipients

The aim of this study was to determine whether plasma concentrations of the acyl (AcMPAG) and phenolic (MPAG) glucuronide metabolites of mycophenolic acid (MPA) were related to diarrhoea in renal transplant patients on mycophenolate mofetil (MMF) with cyclosporine (CsA) or tacrolimus (TCL). Blood samples (0, 30, 120 min) were taken at days 3, 10, week 4, months 3, 6 and 12 for determination of MPA, MPAG and AcMPAG. MPA-AUC was estimated using validated algorithms. Two hour AUCs were calculated for MPAG and AcMPAG. Immunosuppressive therapy consisted of CsA/MMF (n= 110) and of TCL/MMF (n= 180). In 70/290 (24%) patients 86 episodes of diarrhoea were recorded during 12 months. Significantly more patients on TCL (31.1%) suffered from diarrhea compared to CsA (12.7%). MMF dose, MPA-AUC and the 2 h AUCs of MPAG and AcMPAG did not differ between patients with and without diarrhoea. Plasma AcMPAG and MPAG concentrations were substantially higher in patients on CsA compared with TCL, while MPA-AUC was lower in the former group. These data support the concept that CsA inhibits the biliary excretion of MPAG and AcMPAG, thereby potentially reducing the risk of intestinal injury through enterohepatic recycling of MPA and its metabolites.

Therapeutic drug monitoring of mycophenolic acid: does it improve patient outcome?

Treatment with the immunosuppressive agent mycophenolate mofetil (MMF) decreases the risk of rejection after renal transplantation and improves graft survival compared with azathioprine. The exposure to the active metabolite mycophenolic acid (MPA) is correlated to the risk of developing acute rejection. The interpatient variability in exposure of MPA is wide relative to the proposed therapeutic window of the MPA AUC(0 12) (30 - 60 mg.h/l). The pharmacokinetics of MPA are influenced by patient characteristics such as gender, time after transplantation, serum albumin concentration, renal function, comedication and pharmacogenetic factors. Therapeutic drug monitoring is likely to reduce inter-patient variability. Limited sampling strategies are used to predict the full AUC(0 12). Three prospective randomised studies compared concentration controlled MMF therapy to a fixed-dose regimen. Preliminary outcomes of these studies showed conflicting results and longer follow up is needed to further clarify the role of therapeutic drug monitoring in increasing the therapeutic potential of MMF.

Mycophenolic acid trough level monitoring in solid organ transplant recipients treated with mycophenolate mofetil: association with clinical outcome

BACKGROUND

Mycophenolate mofetil (MMF) is widely and successfully used in immunosuppressive regimens for the prophylaxis of organ rejection following transplantation. Conventionally, it is administered at a fixed dose without serial measurements of plasma concentrations of mycophenolic acid (MPA), the active metabolite. Recently, there has been an increased interest in therapeutic drug monitoring (TDM) of MMF therapy to optimize the benefit/risk index of the drug. Predose trough samples of MPA are considered most convenient and economic, thereby allowing an increased use of TDM in the transplant setting. However, the added value of TDM for MMF therapy is still under debate.

OBJECTIVE

This paper reviews (based on a systematic PubMed and EMBASE search, 1995-June 2006) the current evidence of the usefulness and clinical relevance of MPA trough level monitoring during MMF therapy in solid organ transplantation.

FINDINGS AND CONCLUSIONS

Based on data available in the public domain, the contribution of MPA trough level monitoring during MMF therapy in solid organ transplant recipients remains unproven. Available studies have limitations and report conflicting results. There is a lack of prospective randomized trials, particularly in pediatric renal transplant recipients and in cardiac and liver transplantation. While there is a suggestion that there may be a relationship between efficacy and MPA trough levels, the majority of studies showed no correlation between MPA plasma concentrations and adverse effects. Based on current evidence, the adherence to presently recommended target ranges for MPA troughs in solid organ transplantation cannot assure an improved clinical outcome with MMF therapy. Whether MPA trough level monitoring leads to improved efficacy and less toxicity is currently subject to a large randomized trial; final results are eagerly awaited.