Mycophenolic acid concentrations are associated with cardiac allograft rejection

Efficacy and Safety of Mycophenolate Mofetil In De Novo Renal Transplantation in a Retrospective Cohort of Transplant Recipients in Colombia-Esmitren Study

BACKGROUND

To describe and establish the efficacy and safety of Mycophenolate Mofetil (Micoflavin) in patients with de novo renal transplantation during one-year post-transplant follow-up. As secondary objectives, the behavior of mycophenolic acid (MPA) C0 levels in this population, the relationship between MPA levels and renal function of the grafts, the incidence of acute rejection, and the incidence of adverse effects were evaluated.

METHODS

A prospective cohort study was conducted on patients who received a first kidney transplant from a deceased donor between March 1, 2021, and February 28, 2022, at the Alma Mater of Antioquia Hospital of the Antioquia's University, in Medellín, Colombia. MPA C0 levels were taken from the patients on days 15, 30, 90, 180, and 360 after the kidney transplantation.

RESULTS

Patients presented MPA therapeutic levels in the study. The average of the MPA levels in the population was 2.5 µg/mL, with an IQR of 2.13 to 3.32. There were 5 acute rejections (27%), but none of the patients with acute rejection presented subtherapeutic levels of mycophenolate. No significant relationship was observed between mycophenolic acid levels and rejection (P = .255). The patients who completed the study had no gastrointestinal intolerance to mycophenolate, cytomegalovirus infections, or significant hematological complications.

CONCLUSIONS

MMF (Micoflavin) maintained mycophenolic acid levels C0 within the therapeutic range, was well tolerated and without the presence of significant adverse events, and maintained stable renal function throughout the follow-up period in the population studied.

Synthesis and Biological Evaluation of Novel Anti-leukemia Proteolysis-Targeting Chimeras in Degradating Inosine Monophosphate Dehydrogenase

Background

Proteolysis-targeting chimera (PROTAC) is a bifunctional molecule comprising a ligand to recognize the targeted protein to be degraded.

Objectives

To use the advantages of the PROTAC technique, we have synthesized novel compounds to degrade inosine monophosphate dehydrogenase (IMPDH) by the proteasome system.

Methods

We describe the synthesis of new PROTACs based on a combination of mycophenolic acid (MPA) as the potent IMPDH inhibitor and pomalidomide as a ligand of E3 ubiquitin ligase via linkers formed from Cu(I)-catalyzed cycloaddition reaction.

Results

All synthesized compounds were investigated against Jurkat cells as acute T-cell leukemia and were potent apoptosis inducers at 50 nM.

Conclusion

The effect of compound 2 in 0.05 μM on IMPDH degradation can be almost prevented by competition with bortezomib as the proteasome inhibitor at 0.1 and 0.5 μM.

Therapeutic Drug Monitoring of Mycophenolic Acid as a Precision Medicine Tool for Heart Transplant Patients: Results of an Observational Pharmacokinetic Pilot Study

In the clinical practice management of heart transplant (HTx), the impact of calcineurin inhibitors co-administration on pharmacokinetics (PKs) of mycophenolic acid (MPA), mycophenolate mofetil (MMF) active drug, is not adequately considered. This retrospective study investigated full MPA-PK profiles by therapeutic drug monitoring (TDM) in 21 HTx recipients treated with MMF combined with cyclosporine (CsA) or tacrolimus (TAC) at a median time of 2.6 months post-transplant. The two treatment groups were compared. We described the main MPA-PK parameters in patients developing acute cellular rejection (ACR) and those who did not. Median dose-adjusted MPA-trough levels and MPA-AUC_0-12h were higher in patients co-treated with TAC than with CsA (p = 0.0001 and p = 0.006, respectively). MPA-C_max and T_max were similar between the two groups, whereas the enterohepatic recirculation biomarker of MPA (MPA-AUC_4-12h) was higher in the MMF and TAC group (p = 0.004). Consistently, MPA clearance was higher in the MMF and CsA group (p = 0.006). In total, 87.5% of ACR patients were treated with MMF and CsA, presenting a lower MPA-AUC_0-12h (p = 0.02). This real-world study suggested the CsA interference on MPA-PK in HTx, evidencing the pivotal role of MPA TDM as a precision medicine tool in the early phase after HTx. A prospective study is mandatory to investigate this approach to HTx clinical outcomes.

Limited Sampling Strategy for Estimation of Mycophenolic Acid Exposure in Adult Chinese Heart Transplant Recipients

Background: With the increasing use of mycophenolic acid (MPA) formulations in organ transplantation, the need for personalized immunosuppressive therapy has become well recognized based on therapeutic drug monitoring (TDM) for avoidance of drug-related toxicity while maintaining efficacy. Few studies have assessed area under the 12 h concentration-time curve of MPA (MPA-AUC_0–12h) in heart transplant recipients who received mycophenolate mofetil (MMF) dispersible tablets (MMFdt). The aim of the study was to investigate the pharmacokinetics (PK) of MMFdt combined with tacrolimus and further to develop a practical method for estimation of MPA-AUC_0–12h using a limited sampling strategy (LSS).

Methods: A prospective study in a single center was performed in patients who continuously administrated with MMFdt or MMF capsule (MMFc) for at least 7 days after cardiac transplantation from 2018 to 2020. A total of 48 Chinese adult heart transplant recipients were enrolled. Blood samples were collected before and 0.5, 1, 1.5, 2, 4, 6, 8, 10 and 12 h after MMF administration. The validated high-performance liquid chromatography combined with tandem mass spectrometry method was used to measure MPA concentrations. Non-compartmental pharmacokinetic (PK) analysis was applied to calculate the data obtained from individual recipients by WinNonlin. LSS models were developed for MPA-AUC_0–12h prediction with multivariate stepwise regression analysis.

Results: A large inter-individual variability was observed in AUC_0–12h, T_max, C_max, MRT_0–12h, t_1/2 and CL/F after multiple dosing of MMFdt. However, no significant differences were observed between main PK parameters of MMFdt and MMFc. The best estimation of MPA-AUC_0–12h was achieved with four points: MPA-AUC_0–12h = 8.424 + 0.781 × C_0.5 + 1.263 × C₂ + 1.660 × C₄ + 3.022 × C₆ (R² = 0.844). The mean prediction error (MPE) and mean absolute prediction error (MAPE) of MPA-AUC_0–12h were 2.09 ± 14.05% and 11.17 ± 8.52%, respectively. Both internal and external validations showed good applicability for four-point LSS equation.

Conclusion: The results provide strong evidence for the use of LSS model other than a single time-point concentration of MPA when performing TDM. A four-point LSS equation using the concentrations at 0.5, 2, 4, 6 h is recommended to estimate MPA-AUC_0–12h during early period after transplantation in Chinese adult heart transplant recipients receiving MMFdt or MMFc. However, proper internal and external validations with more patients should be conducted in the future.

Personalized Therapy for Mycophenolate: Consensus Report by the International Association of Therapeutic Drug Monitoring and Clinical Toxicology

ABSTRACT

When mycophenolic acid (MPA) was originally marketed for immunosuppressive therapy, fixed doses were recommended by the manufacturer. Awareness of the potential for a more personalized dosing has led to development of methods to estimate MPA area under the curve based on the measurement of drug concentrations in only a few samples. This approach is feasible in the clinical routine and has proven successful in terms of correlation with outcome. However, the search for superior correlates has continued, and numerous studies in search of biomarkers that could better predict the perfect dosage for the individual patient have been published. As it was considered timely for an updated and comprehensive presentation of consensus on the status for personalized treatment with MPA, this report was prepared following an initiative from members of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology (IATDMCT). Topics included are the criteria for analytics, methods to estimate exposure including pharmacometrics, the potential influence of pharmacogenetics, development of biomarkers, and the practical aspects of implementation of target concentration intervention. For selected topics with sufficient evidence, such as the application of limited sampling strategies for MPA area under the curve, graded recommendations on target ranges are presented. To provide a comprehensive review, this report also includes updates on the status of potential biomarkers including those which may be promising but with a low level of evidence. In view of the fact that there are very few new immunosuppressive drugs under development for the transplant field, it is likely that MPA will continue to be prescribed on a large scale in the upcoming years. Discontinuation of therapy due to adverse effects is relatively common, increasing the risk for late rejections, which may contribute to graft loss. Therefore, the continued search for innovative methods to better personalize MPA dosage is warranted.

Impact of SLCO1B3 polymorphisms on clinical outcomes in lung allograft recipients receiving mycophenolic acid

Single-nucleotide polymorphisms (SNPs) in genes involved in mycophenolic acid (MPA) metabolism have been shown to contribute to variable MPA exposure, but their clinical effects are unclear. We aimed to determine if SNPs in key genes in MPA metabolism affect outcomes after lung transplantation. We performed a retrospective cohort study of 275 lung transplant recipients, 228 receiving mycophenolic acid and a control group of 47 receiving azathioprine. Six SNPs known to regulate MPA exposure from the SLCO, UGT and MRP2 families were genotyped. Primary outcome was 1-year survival. Secondary outcomes were 3-year survival, nonminimal (≥A2 or B2) acute rejection, and chronic lung allograft dysfunction (CLAD). Statistical analyses included time-to-event Kaplan-Meier with log-rank test and Cox regression modeling. We found that SLCO1B3 SNPs rs4149117 and rs7311358 were associated with decreased 1-year survival [rs7311358 HR 7.76 (1.37-44.04), p = 0.021; rs4149117 HR 7.28 (1.27-41.78), p = 0.026], increased risk for nonminimal acute rejection [rs4149117 TT334/T334G: OR 2.01 (1.06-3.81), p = 0.031; rs7311358 GG699/G699A: OR 2.18 (1.13-4.21) p = 0.019] and lower survival through 3 years for MPA patients but not for azathioprine patients. MPA carriers of either SLCO1B3 SNP had shorter survival after CLAD diagnosis (rs4149117 p = 0.048, rs7311358 p = 0.023). For the MPA patients, Cox regression modeling demonstrated that both SNPs remained independent risk factors for death. We conclude that hypofunctional SNPs in the SLCO1B3 gene are associated with an increased risk for acute rejection and allograft failure in lung transplant recipients treated with MPA.

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.

Usefulness of limited sampling strategy for mycophenolic acid area under the curve considering postoperative days in living-donor renal transplant recipients with concomitant prolonged-release tacrolimus

Background

The optimal dose of mycophenolate mofetil (MMF) in renal transplant patients has been recommended to be decided on the basis of area under the concentration-time curve (AUC_0-12) of mycophenolic acid (MPA). Although meta-analysis has revealed that postoperative day (POD) is an influencing factor in MPA pharmacokinetics, there are no reports regarding a limited sampling strategy (LSS) for MPA AUC in consideration of POD. The aim of this study was to construct of an LSS considering POD that appropriately expresses the MPA AUC following renal transplantation and evaluation of the usefulness.

Methods

Serum concentration–time profiles (measured AUC_0-12) comprising nine sampling points over 12 h were analyzed in 36 living-donor renal transplant recipients after MMF administration with concomitant once-daily prolonged-release tacrolimus. Two LSSs were developed by stepwise multiple regression analysis (Method A: not classified by PODs; Method B: classified by PODs into POD < 31 and POD ≥ 31). Each LSS comprised four blood-sampling points within 6 h after MMF administration. Precision and reliability were verified by using root-mean-square error (RMSE), correlation coefficient (R²), and coefficient of determination (q²) by using leave-one-out cross-validation. The absolute values of the difference between measured and estimated AUCs (delta AUC) were compared for both estimating equations.

Results

One-hundred samples obtained from 36 recipients for AUC_0-12 comprised POD < 31 (n = 39) and POD ≥ 31 (n = 61). Estimation of AUC_0-12 by Method B resulted in better accuracy and reliability (Method A: RMSE = 5.5, R² = 0.85, q² = 0.83; Method B: POD < 31: RMSE = 5.5, R² = 0.86, q² = 0.83; POD ≥ 31: RMSE = 3.9, R² = 0.92, q² = 0.89) and significantly lower median delta AUC compared with that by Method A (delta AUC: 2.6 (0.0–11.6) v.s. 3.9 (0.1–18.1), p = 0.032).

Conclusion

These results suggest that LSS, classified as POD < 31 or POD > 31, would provide more accurate and reliable estimation of MPA AUC_0-12 in Japanese living-donor renal transplant patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s40780-017-0086-7) contains supplementary material, which is available to authorized users.

Pharmacokinetics of Mycophenolic Acid and Its Glucuronidated Metabolites in Stable Lung Transplant Recipients

Background:

Mycophenolic acid (MPA) is the active metabolite of mycophenolate mofetil, an immunosuppressive agent commonly used in solid organ transplantation. MPA is metabolized to the inactive metabolite 7-O-mycophenolic acid glucuronide (MPAG) and the active metabolite acyl glucuronide (AcMPAG). Pharmacokinetic profiling of MPA by determining AUC is a tool for determining drug exposure. Many studies, conducted primarily in kidney and some heart and liver transplant recipients, have shown wide interpatient variability in MPA's pharmacokinetic parameters. There have been few studies in the lung transplant group and, even though the lung is not involved in drug elimination, these patients may have different MPA pharmacokinetic characteristics.

Objective:

To characterize the pharmacokinetic parameters and metabolic ratios of MPA in stable adult lung transplant recipients.

Methods:

In an open-label manner, lung transplant recipients were recruited. Blood samples were obtained at 0, 0.3, 0.6, 1, 1.5, 2, 4, 6, 8, 10, and 12 hours postdose. Plasma was separated and acidified for drug concentration analysis (MPA, MPAG, AcMPAG) by an HPLC–ultraviolet detection method. Conventional pharmacokinetic parameters were determined via noncompartmental methods.

Results:

There was large interpatient variability in all pharmacokinetic parameters of MPA, MPAG, and AcMPAG. Similar variability was observed after stratifying patients into concomitant medication groups: cyclosporine and tacrolimus. There was a trend for the tacrolimus group to have a higher dose-normalized AUC, higher AUC, lower apparent clearance, and lower AUC ratio of AcMPAG/MPA compared with the cyclosporine group. In addition, the cyclosporine group had a lower minimum concentration and higher AUC ratio of MPAG/MPA than did the tacrolimus group (p < 0.05).

Conclusions:

Because of the large interpatient variability in the pharmacokinetic parameters of MPA, MPAG, and AcMPAG, therapeutic drug monitoring of MPA and its metabolites in lung transplant recipients may be beneficial.

Clinical Pharmacokinetic and Pharmacodynamic Monitoring for Mycophenolate Mofetil

The use of mycophenolate mofetil (MMF), in combination with cyclosporine (CsA) or tacrolimus (FK) and corticosteroids, has been shown to improve clinical outcomes through significant reduction in the incidence of acute rejection in solid organ transplant patients. A fixed oral dosing regimen of 1 or 1.5 g MMF twice daily received Food and Drug Administration approval in 1995 with no recommendations for concentration monitoring at that time. Subsequent evidence has generated substantial debate on the need of clinical monitoring for MMF. This article summarizes the rationale, evidence, and approaches of clinical monitoring for MMF. Mycophenolic acid (MPA), the active moiety of MMF, noncompetitively inhibits the enzyme inosine monophosphate dehydrogenase (IMPDH), which is the target enzyme for MPA. Pharmacokinetic monitoring, by use of MPA predose or MPA area under the concentration-time curve (AUC) values, and pharmacodynamic monitoring by analysis of inhibition of IMPDH have been evaluated in organ transplant patients. The possibility of drug interactions between other immunosuppressive agents has also received attention recently. The clinical implications of drug interactions are discussed in this article.

New Antiproliferative Immunosuppressive Agents

Since the early 1980s, the combination of cyclosporine, azathioprine, and prednisone has been the mainstay tripledrug immunosuppressive regimen used in transplantation. However, advances in drug research, design, and development have allowed for the introduction of new agents that have greatly increased the number of immunosuppressive agents available for use in transplant recipients. Particularly, the newer antiproliferative immunosuppressive drugs (agents that directly inhibit the proliferation of T and B lymphocytes) have had an important impact on patient outcomes posttransplant. These agents are mycophenolate mofetil and sirolimus.

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).

Mycophenolate monitoring in liver, thoracic, pancreas, and small bowel transplantation: a consensus report

Assessing the value of mycophenolic acid (MPA) monitoring outside renal transplantation is hindered by the absence of any trial comparing fixed-dose and concentration-controlled therapy. However, in liver and thoracic transplantation particularly, clinical trials, observational studies with comparison groups, and case series have described MPA efficacy, exposure/efficacy relationships, pharmacokinetic variability, and clinical outcomes relating to plasma MPA concentrations. On the basis of this evidence, this report identifies MPA as an immunosuppressant for which the combination of variable disposition, efficacy, and adverse effects contributes to interindividual differences seemingly in excess of those optimal for a fixed-dosage mycophenolate regimen. Combined with experiences of MPA monitoring in other transplant indications, the data have been rationalized to define circumstances in which measurement of MPA concentrations can contribute to improved management of mycophenolate therapy in nonrenal transplant recipients.

Novel strategies for immune monitoring in kidney transplant recipients

The ongoing quandary in kidney transplantation is discovering methods to prolong graft survival. To achieve this, there is a search for optimal methods to use immunosuppressive therapy, where rejection and chronic graft damage is minimized without causing an increased risk of infections, malignancy, or toxicities. The purpose of this review was to discuss the limitations of current immunosuppressant drug monitoring as well as the clinical application of novel methods of monitoring both immunosuppressants and the immune reaction within the allograft.

Pharmacokinetic optimization of immunosuppressive therapy in thoracic transplantation: part II

Part I of this article, which appeared in the previous issue of the Journal, reviewed calcineurin inhibitors--ciclosporin and tacrolimus. In part II, we review the pharmacokinetics and therapeutic drug monitoring of mycophenolate and mammalian target of rapamycin inhibitors--sirolimus and everolimus--in thoracic transplantation, and we provide an overall discussion and suggest various areas for future study.

Pharmacokinetic optimization of immunosuppressive therapy in thoracic transplantation: part I

Although immunosuppressive treatments and therapeutic drug monitoring (TDM) have significantly contributed to the increased success of thoracic transplantation, there is currently no consensus on the best immunosuppressive strategies. Maintenance therapy typically consists of a triple-drug regimen including corticosteroids, a calcineurin inhibitor (ciclosporin or tacrolimus) and either a purine synthesis antagonist (mycophenolate mofetil or azathioprine) or a mammalian target of rapamycin inhibitor (sirolimus or everolimus). The incidence of acute and chronic rejection and of mortality after thoracic transplantation is still high compared with other types of solid organ transplantation. The high allogenicity and immunogenicity of the lungs justify the use of higher doses of immunosuppressants, putting lung transplant recipients at a higher risk of drug-induced toxicities. All immunosuppressants are characterized by large intra- and interindividual variability of their pharmacokinetics and by a narrow therapeutic index. It is essential to know their pharmacokinetic properties and to use them for treatment individualization through TDM in order to improve the treatment outcome. Unlike the kidneys and the liver, the heart and the lungs are not directly involved in drug metabolism and elimination, which may be the cause of pharmacokinetic differences between patients from all of these transplant groups. TDM is mandatory for most immunosuppressants and has become an integral part of immunosuppressive drug therapy. It is usually based on trough concentration (C(0)) monitoring, but other TDM tools include the area under the concentration-time curve (AUC) over the (12-hour) dosage interval or the AUC over the first 4 hours post-dose, as well as other single concentration-time points such as the concentration at 2 hours. Given the peculiarities of thoracic transplantation, a review of the pharmacokinetics and TDM of the main immunosuppressants used in thoracic transplantation is presented in this article. Even more so than in other solid organ transplant populations, their pharmacokinetics are characterized by wide intra- and interindividual variability in thoracic transplant recipients. The pharmacokinetics of ciclosporin in heart and lung transplant recipients have been explored in a number of studies, but less is known about the pharmacokinetics of mycophenolate mofetil and tacrolimus in these populations, and there are hardly any studies on the pharmacokinetics of sirolimus and everolimus. Given the increased use of these molecules in thoracic transplant recipients, their pharmacokinetics deserve to be explored in depth. There are very few data, some of which are conflicting, on the practices and outcomes of TDM of immunosuppressants after thoracic transplantation. The development of sophisticated TDM tools dedicated to thoracic transplantation are awaited in order to accurately evaluate the patients' exposure to drugs in general and, in particular, to immunosuppressants. Finally, large cohort TDM studies need to be conducted in thoracic transplant patients in order to identify the most predictive exposure indices and their target values, and to validate the clinical usefulness of improved TDM in these conditions. In part I of the article, we review the pharmacokinetics and TDM of calcineurin inhibitors. In part II, we will review the pharmacokinetics and TDM of mycophenolate and mammalian target of rapamycin inhibitors, and provide an overall discussion along with perspectives.

Mycophenolate blood level monitoring: recent progress

The concentration-effect relationship for mycophenolic acid (MPA), and the high variability in MPA concentrations in patients on standard dose mycophenolate mofetil (MMF) therapy, for some centers has provided enough evidence to implement therapeutic drug monitoring (TDM) for MMF in daily practice. Two randomized trials Adaption de Posologie du MMF en Greffe Renale (APOMYGRE) and fixed-dose versus concentration controlled (FDCC) investigated the added benefit of TDM for MMF in renal transplant recipients. The APOMYGRE study showed a significant reduction in the incidence of acute rejection in concentration-controlled patients, while the FDCC study had a negative outcome, despite a similar study design. Although it was expected that these prospective trials would give the final answer to the question of whether or not TDM for MMF would be of benefit, it seems that the studies have not had much impact on patient management. Several trials have shown the importance of early adequate exposure to MPA in the first week after transplantation. As it will be hard to improve MPA exposure with TDM, this early, ongoing study now investigates the use of an increased starting dose. The increased starting dose will avoid underexposure to MPA in higher proportions of patients shortly after transplantation but may result in more toxicity in patients with MPA exposures exceeding the upper threshold of the therapeutic window.

Fixed- or controlled-dose mycophenolate mofetil with standard- or reduced-dose calcineurin inhibitors: the Opticept trial

Mycophenolate mofetil (MMF) was developed with cyclosporine as a fixed-dose immunosuppressant. More recent data indicate a relationship between mycophenolic acid (MPA) exposure in individuals and clinical endpoints of rejection and toxicity. This 2-year, open-label, randomized, multicenter trial compared the efficacy and safety of concentration-controlled MMF (MMF(CC)) dosing with a fixed-dose regimen in 720 kidney recipients. Patients received either (A) MMF(CC) and reduced-level calcineurin inhibitor (MMF(CC)/CNI(RL)); (B) MMF(CC) and standard-level CNI (MMF(CC)/CNI(SL)); or (C) fixed-dose MMF and CNI(SL) (MMF(FD)/CNI(SL)). Antibody induction and steroid use were according to center practice. The primary endpoint was noninferiority (alpha= 0.05) of group A versus group C for treatment failure (including biopsy-proven acute rejection [BPAR], graft loss and death) at 1 year. Although mean CNI trough levels in group A did not reach the prespecified targets, they were statistically lower than those in groups B and C (p < or = 0.01 for each comparison). BPAR rates (8.5%) were low across groups. Group A had 19% fewer treatment failures (23% vs. 28%, p = 0.18). MMF doses were highest (p < 0.05), with withdrawals for adverse events the fewest (p = 0.02), in group A. Of the 80% of subjects taking tacrolimus (Tac), those with higher MPA exposure had significantly less rejection (p < 0.001) and diarrhea correlated with Tac, but not with MPA levels. Thus, MMF(CC) with low-dose CNI resulted in outcomes not inferior to those with standard CNI exposure and MMF(FD), indicating potential utility of MMF(CC) in CNI-sparing regimens.

Pharmacokinetics of mycophenolic acid and its glucuronide metabolites in stable adult liver transplant recipients with renal dysfunction on a low-dose calcineurin inhibitor regimen and mycophenolate mofetil

Low-dose calcineurin inhibitors (CNIs) in combination with a fixed dose (2 g/d) of mycophenolate mofetil (MMF) are a strategy to minimize exposure to cyclosporine (CSA) or tacrolimus (TAC) and thus reduce CNI-related side effects. This study compared the pharmacokinetics (PK) of mycophenolic acid (MPA) and its glucuronide metabolites in stable adult liver transplant recipients with moderately impaired renal function converted from a standard to a low-dose CNI regimen in combination with a fixed dose of MMF. Full 12-hour PK profiles of MPA, free MPA, the aryl glucuronide (MPAG), and the acyl glucuronide (AcMPAG) were obtained from 30 stable liver transplant patients on low-dose CNI (CSA, n = 12; TAC, n = 18) therapy at least 3 months after initiation of low-dose therapy. Predose CSA and TAC concentrations (quantified by liquid chromatography-tandem mass spectrometry) ranged from 17 to 35 and 1.1 to 3.7 microg/L, respectively. The PK variables for MPA, MPAG, AcMPAG, and free MPA displayed wide interindividual variability. Of note was the observation that there were no significant differences in the exposure to MPA, MPAG, and free MPA between the CSA and TAC groups. MPA area under the concentration-time curves (AUCs) ranged from 31.8 to 102.1 (median: 52.9) mg.h(-1).L(-1) in the CSA group and from 22.9 to 144.8 (median: 55.9) mg.h(-1).L(-1) in the TAC group. The AcMPAG AUC on patients under low-dose CSA therapy was higher than that observed under patients on low-dose TAC therapy, although this did not quite reach statistical significance (P = 0.057). Patients receiving CSA had a significantly higher AcMPAG Cmax but not AcMPAG AUC, suggesting that only peak CSA concentrations on a low-dose CSA regimen are sufficient to impair the biliary excretion of AcMPAG. In summary, the influence of CSA on the exposure to MPA was attenuated in stable adult liver transplant recipients on a low-dose CNI therapy in combination with a fixed dose of MMF as compared with patients on a standard CNI therapy. Dose adjustment according to drug concentration measurements is recommended to optimize dosing of MMF and to maintain adequate immunosuppression in patients converted to low-dose CNI therapy.

Defining algorithms for efficient therapeutic drug monitoring of mycophenolate mofetil in heart transplant recipients

Pharmacokinetics of mycophenolate mofetil (MMF) show large interindividual variability. Concentration-controlled dosing of MMF based on routine therapeutic drug monitoring, which requires area under the concentration-time curve (mycophenolic acid [MPA]-AUC0-12h) determinations, is uncommon. Dose adjustments are based on predose concentrations (C0h) or side effects. The aim of this study was to compare C0h with postdose concentrations (C0.5h-C12h) and to develop practical methods for estimation of MPA-AUCs on the basis of a limited sampling strategy (LSS) in heart transplant recipients under MMF and tacrolimus maintenance immunosuppression. Full MPA-AUC0-12h profiles were generated by high-performance liquid chromatography in 28 patients. Statistical analysis for MPA-AUC0-12h was performed by a case resampling bootstrap method. Bland and Altmann analysis was performed to test agreement between "predicted AUC" and "measured AUC." C1h provided the highest coefficient of determination (r2 = 0.57) among the concentrations determined during the 12-hour interval, which were correlated with AUC. All other MPA levels were better surrogates of the MPA-AUC0-12h when compared with C0h (r2 = 0.14). The best estimation of MPA-AUC0-12h was achieved with four sampling points with the algorithm AUC = 1.25*C1h + 5.29*C4h + 2.90*C8h + 3.61*C10h (r2 = 0.95). Since LSS with four time points appeared unpractical, the authors prefer models with three or two points. To optimize practicability, LSS with sample points within the first 2 hours were evaluated resulting in the algorithms: AUC = 1.09*C0.5h + 1.19*C1h + 3.60*C2h (r2 = 0.84) and AUC = 1.65*C0.5h + 4.74*C2h (r2 = 0.75) for three and two sample points, respectively. The results provide strong evidence for the use of either LSS or the use of time points other than C0h for therapeutic drug monitoring of MMF. Using the algorithms for the estimation of MPA-AUC0-12h based on LSS within the first 2 hours after MMF dosing may help to optimize treatment with MMF by individualization of dosing.

Pharmacokinetics of mycophenolate mofetil and its glucuronide metabolites in healthy volunteers

We previously reported that polymorphisms in the UGT2B7 and UGT1A9 genes are associated with significant alteration in the disposition of mycophenolic acid (MPA) in healthy volunteers. Aim: This study further evaluates the impact of genetic polymorphisms at the UGT1A1, UGT1A7 and ABCC2 loci. Methods: Genetic analyses of five UGT candidate genes and ABCC2 were completed on 47 healthy subjects who received a single dose of 1.5 g mycophenolate mofetil and completed a 12-h pharmacokinetic profile. Results: Multivariate analyses indicate that the ABCC2 -24T promoter polymorphism is associated with a 25% increase in acyl mycophenolic acid phenolic glucuronide level. Subjects with combined ABCC2 -24T and UGT1A9*3 genotypes present a 169% increased exposure to AcMPAG. Homozygosity for UGT1A7 387G/391A (129Lys/131Lys) is associated with a modest but significant 7% reduction in MPA level. When these additional genetic factors are considered in the model, the effects of previously described UGT1A9 and UGT2B7 variations remain significant. No significant effect is observed for UGT1A1*28, UGT1A7 622T/C (Trp208Arg), UGT1A9 -440TC/-331CT, UGT1A9 -118 TA9/10 and seven other ABCC2 SNPs. Conclusion: We demonstrate that MPA disposition is a multigenic process, and that additional studies are required to ascertain the relationship between UGT, ABCC2 genotypes and MPA pharmacokinetics in transplant recipients.

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.

Validation of limited sampling strategy for the estimation of mycophenolic acid exposure in Chinese adult liver transplant recipients

Mycophenolate mofetil (MMF) is indicated as immunosuppressive therapy in liver transplantation. The abbreviated models for the estimation of mycophenolic acid (MPA) area under the concentration-time curve (AUC) have been established by limited sampling strategies (LSSs) in adult liver transplant recipients. In the current study, the performance of the abbreviated models to predict MPA exposure was validated in an independent group of patients. A total of 30 MPA pharmacokinetic profiles from 30 liver transplant recipients receiving MMF in combination with tacrolimus were used to compare 8 models' performance with a full 10 time-point MPA-AUC. Linear regression analysis and Bland-Altman analysis were used to compare the estimated MPA-AUC0-12h from each model against the measured MPA-AUC0-12h. A wide range of agreement was shown when estimated MPA-AUC0-12h was compared with measured MPA-AUC0-12h, and the range of coefficient of determination (r2) was from 0.479 to 0.936. The model based on MPA pharmacokinetic parameters C1h, C2h, C6h, and C8h had the best ability to predict measured MPA-AUC0-12h, with the best coefficient of determination (r2=0.936), the excellent prediction bias (2.18%), the best prediction precision (5.11%), and the best prediction variation (2SD=+/-7.88 mg.h/L). However, the model based on MPA pharmacokinetic sampling time points C1h, C2h, and C4h was more suitable when concerned with clinical convenience, which had shorter sampling interval, an excellent coefficient of determination (r2=0.795), an excellent prediction bias (3.48%), an acceptable prediction precision (14.37%), and a good prediction variation (2SD=+/-13.23 mg.h/L). Measured MPA-AUC0-12h could be best predicted by using MPA pharmacokinetic parameters C1h, C2h, C6h, and C8h. The model based on MPA pharmacokinetic parameters C1h, C2h, and C4h was more feasible in clinical application.

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.

Limited sampling strategy for mycophenolic acid in Japanese heart transplant recipients: comparison of cyclosporin and tacrolimus treatment

BACKGROUND

The purpose of the study was to characterize the pharmacokinetics of mycophenolic acid (MPA) in Japanese heart transplant recipients and to find the time point that has the best correlation with the MPA area under the plasma concentration curve (AUC).

METHODS AND RESULTS

Twenty-two Japanese recipients treated with mycophenolate mofetil were evaluated in the study. Approximately 9 months after transplantation, the area under the MPA serum concentration-time curve from 0 to 12 h (AUC(0-12 h)) was evaluated. The MPA AUC(0-12 h) h values in the cyclosporine (CsA) and tacrolimus (FK) groups ranged from 13.11 to 50.98 mug . h/ml and from 39.19 to 93.18 mug . h/ml, respectively. Fourteen models were developed and analyzed for their ability to estimate the MPA AUC(0-12 h) based on a limited number of samples in the CsA group. Sixteen models were developed in the FK group. The best model for predicting the full MPA AUC(0-12 h) in the CsA group was a 3-time-point model that included C(0 h), C(1 h) and C(2 h) (r(2), 0.96; mean prediction error, 0.15+/-7.85%); a 2-time-point model that included C(0 h), and C(2 h) (r(2), 0.94; mean prediction error, 0.495+/-10.35%) was also reliable. In the FK group, a 3-time-point model that included C(1 h), C(2 h) and C(4h) (r(2), 0.73; mean prediction error, 2.73+/-17.09%) was the best model for predicting the full MPA AUC(0-12 h), but it was not reliable in clinical practice.

CONCLUSION

A 3-(C(0 h), C(1 h) and C(2 h)) and a 2-time-point model (C(0 h) and C(2 h)) are useful for predicting the full MPA AUC(0-12 h) in Japanese heart transplant recipients treated with CsA but not with FK.

Therapeutic drug measurement of mycophenolic acid derivatives in transplant patients

INTRODUCTION

Mycophenolic acid, the active metabolite of the prodrug mycophenolate mofetil, is widely used as an immunosuppressive agent in transplant patients for the prophylaxis of acute rejection. Recent prospective trials suggested the need for therapeutic drug monitoring, which raises the necessity to acquire accurate methods to measure MPA and its metabolites.

OBJECTIVE

Present an overview of the reasons to monitor MPA and its metabolites as well as a review of the currently available methods for their determination.

METHODS

Articles published from January 1992 to December 2006 were reviewed.

RESULTS

Most of the cited references use either chromatographic or immunoassay techniques. Basic information about biological samples used for the analysis, sample preparation, stationary phase, mobile phase, detection mode and validation data are discussed. Current information suggests the feasibility to set up method(s) to monitor MPA and its metabolites in most centers.

Limited Sampling Strategy for the Estimation of Mycophenolic Acid Area Under the Plasma Concentration-Time Curve in Adult Patients Undergoing Liver Transplant

Mycophenolate mofetil (MMF), the oral prodrug of mycophenolic acid (MPA), is increasingly used in liver transplantation and plays a central role in the immunosuppressive regimen in liver transplantation. To study pharmacokinetic-pharmacodynamic relationships and therapeutic drug monitoring of MPA in the clinical setting, limited sampling strategies have been investigated for the estimation of MPA areas under the curves (AUCs). Thirty-eight adult patients undergoing liver transplant (31 males, seven females) receiving 1.0 g MMF twice daily and concomitant tacrolimus provided a total of 72 pharmacokinetic profiles. Multiple stepwise regression analysis was used to determine the algorithms for limited sampling strategies. Twenty-eight one-, two-, three-, and four-sampling estimation models were fitted (r = 0.288-0.964) to all the profiles using linear regression and were used to estimate MPA AUC0-12h comparing those estimates with the corresponding AUC0-12h values calculated with the linear trapezoidal rule, including all 10 timed MPA concentrations. The four-point estimates at C1h, C2h, C6h, and C8h resulted in the best correlation between estimated AUC and true AUC when using the formula AUC = 6.03 + 0.89C1h + 1.94C2h + 2.24C6h + 4.64 C8h (r = 0.911). Bland and Altman analysis revealed good agreement between estimated AUC and AUC from the full profile. This limited sampling strategy provides an effective approach for estimation of full MPA AUC0-12h in patients undergoing liver transplant receiving concomitant tacrolimus therapy.

Clinical pharmacokinetics and pharmacodynamics of mycophenolate in solid organ transplant recipients

This review aims to provide an extensive overview of the literature on the clinical pharmacokinetics of mycophenolate in solid organ transplantation and a briefer summary of current pharmacodynamic information. Strategies are suggested for further optimisation of mycophenolate therapy and areas where additional research is warranted are highlighted. Mycophenolate has gained widespread acceptance as the antimetabolite immunosuppressant of choice in organ transplant regimens. Mycophenolic acid (MPA) is the active drug moiety. Currently, two mycophenolate compounds are available, mycophenolate mofetil and enteric-coated (EC) mycophenolate sodium. MPA is a potent, selective and reversible inhibitor of inosine monophosphate dehydrogenase (IMPDH), leading to eventual arrest of T- and B-lymphocyte proliferation. Mycophenolate mofetil and EC-mycophenolate sodium are essentially completely hydrolysed to MPA by esterases in the gut wall, blood, liver and tissue. Oral bioavailability of MPA, subsequent to mycophenolate mofetil administration, ranges from 80.7% to 94%. EC-mycophenolate sodium has an absolute bioavailability of MPA of approximately 72%. MPA binds 97-99% to serum albumin in patients with normal renal and liver function. It is metabolised in the liver, gastrointestinal tract and kidney by uridine diphosphate gluconosyltransferases (UGTs). 7-O-MPA-glucuronide (MPAG) is the major metabolite of MPA. MPAG is usually present in the plasma at 20- to 100-fold higher concentrations than MPA, but it is not pharmacologically active. At least three minor metabolites are also formed, of which an acyl-glucuronide has pharmacological potency comparable to MPA. MPAG is excreted into the urine via active tubular secretion and into the bile by multi-drug resistance protein 2 (MRP-2). MPAG is de-conjugated back to MPA by gut bacteria and then reabsorbed in the colon. Mycophenolate mofetil and EC-mycophenolate sodium display linear pharmacokinetics. Following mycophenolate mofetil administration, MPA maximum concentration usually occurs in 1-2 hours. EC-mycophenolate sodium exhibits a median lag time in absorption of MPA from 0.25 to 1.25 hours. A secondary peak in the concentration-time profile of MPA, due to enterohepatic recirculation, often appears 6-12 hours after dosing. This contributes approximately 40% to the area under the plasma concentration-time curve (AUC). The mean elimination half-life of MPA ranges from 9 to 17 hours. MPA displays large between- and within-subject pharmacokinetic variability. Dose-normalised MPA AUC can vary more than 10-fold. Total MPA concentrations should be interpreted with caution in patients with severe renal impairment, liver disease and hypoalbuminaemia. In such individuals, MPA and MPAG plasma protein binding may be altered, changing the fraction of free MPA available. Apparent oral clearance (CL/F) of total MPA appears to increase in proportion to the increased free fraction, with a reduction in total MPA AUC. However, there may be little change in the MPA free concentration. Ciclosporin inhibits biliary excretion of MPAG by MRP-2, reducing enterohepatic recirculation of MPA. Exposure to MPA when mycophenolate mofetil is given in combination with ciclosporin is approximately 30-40% lower than when given alone or with tacrolimus or sirolimus. High dosages of corticosteroids may induce expression of UGT, reducing exposure to MPA. Other co-medications can interfere with the absorption, enterohepatic recycling and metabolism of mycophenolate. Most pharmacokinetic investigations of MPA have involved mycophenolate mofetil rather than EC-mycophenolate sodium therapy. In population pharmacokinetic studies, MPA CL/F in adults ranges from 14.1 to 34.9 L/h (ciclosporin co-therapy) and from 11.9 to 25.4 L/h (tacrolimus co-therapy). Patient bodyweight, serum albumin concentration and immunosuppressant co-therapy have a significant influence on CL/F. The majority of pharmacodynamic data on MPA have been obtained in patients receiving mycophenolate mofetil therapy in the first year after kidney transplantation. Low MPA AUC is associated with increased incidence of biopsy-proven acute rejection. Gastrointestinal adverse events may be dose related. Leukopenia and anaemia have been associated with high MPA AUC, trough concentration and metabolite concentrations in some, but not all, studies. High free MPA exposure has been identified as a risk factor for leukopenia in some investigations. Targeting a total MPA AUC from 0 to 12 hours (AUC12) of 30-60 mg.hr/L is likely to minimise the risk of acute rejection and may reduce toxicity. IMPDH monitoring is in the early experimental stage. Individualisation of mycophenolate therapy should lead to improved patient outcomes. MPA AUC12 appears to be the most useful exposure measure for such individualisation. Limited sampling strategies and Bayesian forecasting are practical means of estimating MPA AUC12 without full concentration-time profiling. Target concentration intervention may be particularly useful in the first few months post-transplant and prior to major changes in anti-rejection therapy. In patients with impaired renal or hepatic function or hypoalbuminaemia, free drug measurement could be valuable in further interpretation of MPA exposure.

Relationship between acute rejection and cyclosporine or mycophenolic acid levels in Japanese heart transplantation

BACKGROUND

Cyclosporine (CsA), Mycophenolate mofetil (MMF) and prednisolone (PSL) are widely used for the prevention of acute rejection after heart transplantation. Recently, the serum concentration - time curves (AUC) of CsA and MMF have been demonstrated to be precise predictors of acute rejection.

METHODS AND RESULTS

Fourteen heart transplant patients were treated concomitantly with CsA, MMF, and PSL between May 1999 and November 2005 at the National Cardiovascular Center and of them 3 had acute rejection episodes [International Society for Heart & Lung Transplantation grade 3a]. Two patients (man in his 30 s; woman in her 40 s) had acute rejection with a mycophenolic acid (MPA) AUC(0-12 h) <30 microg x h x ml(-1) and low CsA AUC (AUC(0-4 h); 2,408 ng x h x ml-1, 1,735 ng x h x ml-1). However, 1 patient (man in his 30 s) with a high CsA AUC(0-4 h) (4,019 ng x h x ml-1) did not develop cardiac allograft rejection even if the MMF was temporarily stopped. These 3 patients were investigated to evaluate the relationship between acute rejection and pharmacokinetic parameters, including the CsA C0, C2, AUC(0-4 h) and MPA AUC(0-12 h).

CONCLUSIONS

The findings suggest that a high CsA AUC(0-4 h) may prevent rejection of a cardiac allograft, even if MMF is stopped or drastically reduced.

Pharmacokinetics and variability of mycophenolic acid from enteric-coated mycophenolate sodium compared with mycophenolate mofetil in de novo heart transplant recipients

Sequential pharmacokinetic assessments were performed at five centers within the context of a multicenter, single-blind, randomized clinical trial comparing the efficacy and safety of enteric-coated mycophenolate sodium (EC-MPS, myfortic) and mycophenolate mofetil (MMF, CellCept) in de novo heart transplant recipients. Patients were randomized to either EC-MPS 1080 mg bid or MMF 1500 mg bid, as part of a triple immunosuppressive therapy including cyclosporine microemulsion. Steady-state pharmacokinetic profiles of mycophenolic acid (MPA) and its inactive phenolic glucuronide (MPAG) were assessed at weeks 2, 12, and 52. Pharmacokinetic parameters were evaluated in 32 patients (17 on EC-MPS and 15 on MMF). Dose-normalized peak (C(max,ss)) and area under the curve (AUC(tau,ss)) of MPA and MPAG increased between week 2 and week 12 assessments for both treatments. Comparisons between EC-MPS and MMF showed no statistically significant differences in MPA and MPAG AUC(tau,ss), C(max,ss), and trough (C(min,ss)) values (p-values ranged from 0.225 to 0.990). Consistent with the delayed release characteristics of EC-MPS, C(max,ss) occurred approximately one hour later compared with MMF. Inter-subject coefficients of variation (%CV) for MPA pharmacokinetic parameters of both EC-MPS and MMF were high (37-72% for AUC(tau,ss) at weeks 2 and 12). Also within patients, the pharmacokinetics of MPA varied considerably. Specifically, intra-subject %CVs for MPA AUC(tau,ss), C(max,ss), and C(min,ss) were 28%, 63%, and 34% with EC-MPS and 54%, 139%, and 41% with MMF respectively. These results indicate that a dose of EC-MPS 1080 mg bid in combination with cyclosporine provides adequate systemic MPA exposure in de novo heart transplant patients, comparable with MMF 1500 mg bid. Overall, there is a large inter- and intra-subject variability in MPA pharmacokinetic parameters with both treatments.

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.

Therapeutic Drug Monitoring of Mycophenolic Acid in Solid Organ Transplant Patients Treated With Mycophenolate Mofetil: Review of the Literature

Mycophenolate mofetil (MMF) has conventionally been administered at a fixed dose without routinely monitoring blood levels of mycophenolic acid (MPA), the active metabolite. The contribution of therapeutic drug monitoring (TDM) during MMF therapy remains controversial. A literature review was performed to explore the usefulness of TDM for MPA in solid organ transplantation. In addition, emphasis was placed on the potential clinical benefits and limitations of TDM for MPA. Available studies have limitations and report conflicting results. Although early after transplantation MPA area under the curve might have predictive value for the risk of acute rejection, predose levels appear less reliable. With regard to MPA toxicity, most studies showed no correlation between MPA pharmacokinetics and adverse effects. TDM is hampered by several factors such as the considerable intra-subject variability of MPA pharmacokinetics and the increasing number of different drug combinations. Proposed target ranges are restricted to the early posttransplant period when MMF is used in combination with cyclosporine. The current review of the literature indicates no clear support for a substantial clinical benefit of TDM and more data from prospective randomized trials are needed.

A limited sampling model for estimation of total and unbound mycophenolic acid (MPA) area under the curve (AUC) in hematopoietic cell transplantation (HCT)

OBJECTIVES

Renal transplant patients with suboptimal mycophenolic acid (MPA) areas under the curves (AUCs) are at greater risk of acute rejection. In hematopoietic cell transplantation, a low MPA AUC is also associated with a higher incidence of acute graft versus host disease. Therefore, a limited sampling model was developed and validated to simultaneously estimate total and unbound MPA AUC0-12 in hematopoietic cell transplantation patients.

METHODS

Intensive pharmacokinetic sampling was performed at steady state between days 3 to 7 posttransplant in 73 adult subjects while receiving prophylactic mycophenolate mofetil 1 g per 12 hours orally or intravenously plus cyclosporine. Total and unbound MPA plasma concentrations were measured, and total and unbound AUC0-12 was determined using noncompartmental analysis. Regression analysis was then performed to build IV and PO, total and unbound AUC0-12 models from the first 34 subjects. The predictive performance of these models was tested in the next 39 subjects.

RESULTS

Trough concentrations poorly estimate observed total and unbound AUC0-12 (r<0.48). A model with 3 concentrations (2-, 4-, and 6-hour post start of infusion) best estimated observed total and unbound AUC0-12 after IV dosing (r>0.99). Oral total and unbound AUC0-12 was more difficult to estimate and required at least 4 concentrations (0-, 1-, 2-, and 6-hour post dose) in the model (r>0.85). The predictive performance of the final models was good. Eighty-three percent of IV and 70% of PO AUC0-12 predictions fell within +/-20% of the observed values without significant bias.

CONCLUSION

Trough MPA concentrations do not accurately describe MPA AUC0-12. Three intravenous (2-, 4-, 6-hour post start of infusion) or 4 oral (0-, 1-, 2-, and 6-hour post dose) MPA plasma concentrations measured over a 12-hour dosing interval will estimate the total and unbound AUC0-12 nearly as well as intensive pharmacokinetic sampling with good precision and low bias. This approach simplifies AUC0-12 targeting of MPA post hematopoietic cell transplantation.

Therapeutic drug monitoring of mycophenolate mofetil in transplantation

A roundtable meeting to discuss the use of therapeutic drug monitoring (TDM) to guide immunosuppression with mycophenolate mofetil was held in New York in December 2004. Existing recommendations for the initial months after transplantation were updated. After ensuring adequate levels of mycophenolic acid (MPA, the active metabolite of mycophenolate mofetil) immediately after transplantation, optimal efficacy may require only a few dose adjustments, because intrapatient variability in exposure seems low. Recommendations based on current knowledge were made for posttransplantation sampling time points and for target MPA concentrations. Algorithms for estimating MPA exposure using limited sampling strategies were presented, and a new assay for MPA discussed. It was agreed that because of interpatient variability and the influence of concomitant immunosuppressants, TDM might help optimize outcomes, especially in patients at higher risk of rejection. The value of TDM in the general transplant population will be assessed from large, ongoing, randomized studies.

Mycophenolate mofetil in islet cell transplant: variable pharmacokinetics but good correlation between total and unbound concentrations

The authors investigated the pharmacokinetics of mycophenolic acid over 1 year in 8 Caucasian women undergoing islet cell transplantation. Total mycophenolic acid AUC(0-12) mcg x h/mL before day 60 was 62.1-67.8, declining to 33.6-64.7 thereafter (P = .61). Median total trough concentrations were 1.16-2.90 mcg/mL. Unbound AUC(0-12) was 412-673 ng x h/mL and did not change over time (P = .30). Median percent unbound mycophenolic acid was 0.95% of total concentrations. Individual unbound and total mycophenolic acid concentrations were highly correlated (r2 = 0.94). Total mycophenolic acid trough concentration and total AUC(0-12) were modestly correlated (r2 = 0.65). Intra- and interpatient variability of systemic mycophenolic acid exposure was high. Six patients required dose reductions prior to day 60 due to adverse effects. All subjects achieved insulin independence; 3 later lost graft function. The trend toward higher exposure in the early periods followed by dose reductions suggests that lower initial doses and therapeutic drug monitoring may be necessary.

Mycophenolate mofetil in organ transplantation: focus on metabolism, safety and tolerability

Mycophenolate mofetil (MMF) received its first approval for the prevention of renal allograft rejection in 1995 and has now become the most frequently used antiproliferative agent in maintenance immunosuppressive therapy for kidney, pancreas, liver and heart transplantation. In addition, its use for the treatment of autoimmune diseases steadily increases. This review focuses on the miscellaneous pharmacodynamic properties of the drug, its pharmacokinetics in healthy subjects, recipients of different organ transplants and combination therapy with other pharmaceuticals, as well as its safety profile. The immunosuppressive activity of MMF is thought to derive mainly from the potent and selective inhibition of purine synthesis in both T and B lymphocytes. In contrast to other immunosuppressants on the market, it is metabolised primarily by glucuronidation and lacks nephrotoxicity, cardiovascular toxicity or diabetogenic potential, thus making it a suitable candidate for combination regimens. The most important side effects under MMF include gastrointestinal disorders, of which the underlying mechanisms are not yet fully understood, but seem to be complex and related to both effects of mycophenolic acid and its acyl glucuronide, as well as to decreased -immunity due to general immunosuppression after transplantation.

Review of Major Clinical Trials with Mycophenolate Mofetil in Cardiac Transplantation

Over the past 10 years, the addition of mycophenolate mofetil (MMF) to combination immunosuppressive regimens in cardiac transplant patients has resulted in significant outcomes benefits. Randomized trials and other studies have demonstrated that the use of MMF is associated with a decreased risk of rejection and improved survival. This article will provide an overview of these trials, as well as those evaluating MMF in renal-sparing regimens and in pediatric cardiac transplant recipients. In addition, emerging evidence demonstrating that MMF may provide long-term benefits in reducing cardiac allograft vasculopathy and those evaluating the role of MMF therapeutic drug monitoring in cardiac transplant recipients will be discussed.

Best Single Time Points to Predict the Area-Under-the-Curve in Long-Term Heart Transplant Patients Taking Mycophenolate Mofetil in Combination with Cyclosporine or Tacrolimus

BACKGROUND

The use of C2 levels for therapeutic drug monitoring (TDM) of cyclosporine microemulsion (CsA) has been clinically validated. Routine TDM of tacrolimus and mycophenolate mofetil (MMF) is based on trough (C0) levels and side effects, respectively. The purpose of the present study was to determine the best single time points to assess the area-under-the-curve (AUC(0-12 hours)) in long-term heart transplant patients being treated with MMF in combination with CsA or tacrolimus.

METHODS

We studied the AUC(0-12 hours) in long-term (>1 year), adult heart transplant patients being treated with CsA and MMF (14 patients) and with tacrolimus and MMF (9 patients).

RESULTS

C2 is the best surrogate (r2 = 0.87) of CsA AUC(0-12 hours). Tacrolimus C1 (r2 = 0.78), C2 (r2 = 0.83), C3 (r2 = 0.89) and C4 (r2 = 0.92) correlate better than C0 (r2 = 0.51) with the AUC(0-12 hours). When MMF is combined with CsA, there is poor correlation (r2) of MPA at all measured time points (C0 = 0.49, C2 = 0.09, C3 = 0.23, C4 = 0.44, and C6 = 0.60). When MMF is combined with tacrolimus, MPA C2 (r2 = 0.72), C4 (r2 = 0.86), C6 (r2 = 0.85), and C8 (r2 = 0.93) are better surrogates of the AUC(0-12 hours) compared with C0 (r2 = 0.69).

CONCLUSION

Our results suggest that in long-term heart transplant patients, the calcineurin inhibitor used in combination with MMF affects the correlation between MPA single time points and the AUC(0-12 hours). Future studies should determine the clinical benefit of TDM of tacrolimus and MPA with C2 or C4 compared with C0 and determine the therapeutic ranges. As for CsA-treated patients, CsA TDM should be performed with C2, and the TDM of MMF may be clinically irrelevant.

The Rationale for and Limitations of Therapeutic Drug Monitoring for Mycophenolate Mofetil in Transplantation

The addition of mycophenolate mofetil (MMF) to calcineurin inhibitor-based regimens reduces the incidence of acute rejection after kidney transplantation. The interpatient variability, changes over time of pharmacokinetic parameters, and the potential for drug interactions make the systemic exposure of mycophenolic acid (MPA) unpredictable at a fixed-dose regimen. An increase in plasma concentration of MPA significantly correlates with a decreased likelihood of an acute rejection after kidney or heart transplantation; therefore, a strategy of therapeutic drug monitoring for MMF therapy could improve outcome. Two large randomized, multicenter, prospective trials investigating the added value of therapeutic drug monitoring for MPA, by comparing fixed-dose treatment with concentration-controlled MMF treatment in kidney transplant recipients, are currently ongoing. More data are needed to fully establish the meaning of the reported prognostic value of preoperative inosine monophosphate dehydrogenase (IMPDH) activity, and longitudinal studies monitoring IMPDH activity after transplantation are eagerly awaited.