Pharmacodynamic monitoring of mycophenolate mofetil in stable renal allograft recipients

Why, when and how should immunosuppressive therapy considered in patients with immunoglobulin A nephropathy?

IgA nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. Lifelong mesangial deposition of IgA1 complexes subsist inflammation and nephron loss, but the complex pathogenesis in detail remains unclear. In regard to the heterogeneous course, classical immunosuppressive and specific therapeutic regimens adapted to the loss of renal function will here be discussed in addition to the essential common renal supportive therapy. Renal supportive therapy alleviates secondary, surrogate effects or sequelae on renal function and proteinuria of high intraglomerular pressure and subsequent nephrosclerosis by inhibition of the renin angiotensin system (RAASB). In patients with physiological (ΔGFR < 1·5 ml/min/year) or mild (ΔGFR 1·5-5 ml/min/year) decrease of renal function and proteinuric forms (> 1 g/day after RAASB), corticosteroids have shown a reduction of proteinuria and might protect further loss of renal function. In patients with progressive loss of renal function (ΔGFR > 3 ml/min within 3 months) or a rapidly progressive course with or without crescents in renal biopsy, cyclophosphamide with high-dose corticosteroids as induction therapy and azathioprine maintenance has proved effective in one randomized controlled study of a homogeneous cohort in loss of renal function (ΔGFR). Mycophenolic acid provided further maintenance in non-randomized trials. Differentiated, precise, larger, randomized, placebo-controlled studies focused on the loss of renal function in the heterogeneous forms of IgAN are still lacking. Prospectively, fewer toxic agents will be necessary in the treatment of IgAN.

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.

Randomized trial of enteric-coated mycophenolate sodium versus mycophenolate mofetil in multi-system autoimmune disease

Background

The use of mycophenolate mofetil (MMF) in autoimmune disease is often limited by adverse effects. In this single-centre, open label, parallel design study, we investigated whether enteric-coated mycophenolate sodium (MS) is better tolerated and therefore more efficacious than MMF in primary systemic vasculitis (PSV) and systemic lupus erythematosus (SLE).

Methods

Forty patients with vasculitis or systemic lupus erythematosus (SLE) due to commence MMF for active disease or remission maintenance were randomized to receive either 1440 mg/day MS or 2000 mg/day MMF (18 PSV, 2 SLE per group) in addition to corticosteroids. Random allocation was performed by minimization for age, diagnosis and renal function using a computer algorithm. Twenty-five were treated for active disease (5 first-line therapy, 20 salvage therapy) and 15 for remission maintenance. The composite primary end point was treatment failure and/or drug intolerance over 12 months. Treatment failure was defined as failure to achieve remission by 6 months or disease relapse and treatment intolerance was defined as inability to tolerate and maintain the target dose of MS or MMF within 12 months.

Results

Forty patients were included in the analyses. MS was associated with a lower primary end point rate [hazard ratio (HR) 0.37; 95% CI 0.17–0.80; P = 0.012] (11/20, 55% patients) compared with MMF (17/20, 85% patients). Treatment failure alone was less common in the MS group (HR 0.28; 95% CI 0.095–0.82; P = 0.020), although drug intolerance did not differ between groups (HR 0.53; 95% CI 0.20–1.42; P = 0.21). Despite randomization, patients in the MMF group may have had a higher baseline risk for treatment failure; more MMF patients had refractory disease and granulomatosis with polyangiitis (Wegener's). A glomerular filtration rate (GFR) ≤40 mL/min was associated with intolerance. Serious adverse events were common (55% MMF and 45% MS patients).

Conclusions

No differences in treatment tolerance were observed between the MS and MMF groups. Despite similar treatment intolerance, MS was associated with improved efficacy in PSV and SLE compared with MMF. However, baseline group imbalances in factors potentially affecting remission and relapse may have influenced the results. Treatment intolerance was common and strongly associated with low GFR. Further treatment trials are warranted to investigate the effect of GFR on mycophenolic acid pharmacokinetics and clinical outcomes (ISRCTN83027184; EUDRACT 2005-002207-16; Funding Novartis UK).

Inosine monophosphate dehydrogenase expression and activity are significantly lower in kidney transplant recipients with diabetes mellitus

BACKGROUND

Inosine 5'-monophosphate dehydrogenase (IMPDH) is a target of the immunosuppressive drug, mycophenolic acid (MPA). A 12-hour clinical pharmacokinetic and pharmacodynamic study was conducted to compare IMPDH1 and IMPDH2 gene expression, IMPDHI and IMPDHII protein levels, and enzyme activity between kidney transplant recipients with respect to diabetes status.

METHODS

Nondiabetic (ND, n = 11) and diabetic (D, n = 9) kidney transplant recipients and on nontransplant nondiabetic (n = 10) and diabetic (n = 10) volunteers were included in the study.

RESULTS

Area under the effect curve values for gene expression: IMPDH1 [ND: 22.1 (13.8-31.3) versus D: 4.5 (2.3-6.5), P < 0.001] and IMPDH2 [ND: 15.3 (11.0-21.7) versus D: 6.1 (4.6-8.6), P < 0.001], protein level: IMPDHI [ND: 1.0 (0.5-1.3) versus 0.5 (0.4-0.7), P = 0.002] and IMPDHII [ND: 1.0 (0.6-1.6) versus D: 0.7 (0.6-0.8) P < 0.001] and enzyme activity [ND: 180 (105-245) versus D: 29.9 (15.3-35.6) µmole·s(-1)·mole(-1) adenosine monophosphate, P < 0.001] was significantly lower in transplant recipients with diabetes. Similar results were observed in nontransplanted volunteers. Kinetic studies of MPA-mediated suppression of IMPDH activity in nontransplanted individuals revealed an approximately 2.5-fold lower half-maximum effective concentration (EC50) for diabetic as compared with nondiabetic [ND: 50.2 (49.8-50.7) versus D: 15.8 (15.6-16.3) nmole/L, P = 0.004] volunteers. This difference was not related to several IMPDH gene variants.

CONCLUSIONS

This study indicates a significantly lower IMPDH gene expression, protein level, and enzyme activity in diabetic patients. Further clinical studies in a larger number of patients are warranted to verify whether MPA dosing must be optimized for kidney transplant recipients with diabetes mellitus.

Biomarkers as a tool for management of immunosuppression in transplant patients

Therapeutic drug monitoring is a well-established approach in transplantation medicine to guide immunosuppressive therapy. However, it cannot always predict the effects of immunosuppressive drugs on immune cells, because it does not reflect any aspect of an individual patient's immune system. Pharmacodynamic monitoring is a more recent strategy to provide information about the biologic effect of a specific drug or drug combination on the individual transplant patient. Currently, there is a large number of different biomarkers that either directly (specific markers) or indirectly (global markers) relate to the pharmacodynamic effects of immunosuppressive drugs and are under investigation as potential candidates to be introduced in clinical practice. Such biomarkers may be useful to identify patients at risk of developing acute rejection, infection, or cancer as well as patients who are suitable for minimization of immunosuppressant therapy and may be helpful to manage the timing and rate of immunosuppressant weaning. Serial longitudinal monitoring may allow maintenance of an individualized immunosuppressive regimen. Thus, biomarker monitoring is a potential complementary tool to therapeutic drug monitoring. This review summarizes the current state of knowledge about the use of a number of global or drug-specific pharmacodynamic biomarkers. It is not a comprehensive overview of the literature available, but rather an evidence-based reflection by experts who are intensively involved in scientific work in this field.

Evaluation of inosin-5'-monophosphate dehydrogenase activity during maintenance therapy with tacrolimus

OBJECTIVES

The aim of this study was to identify a target range for inosin-5'-monophosphate dehydrogenase (IMPDH) activity in maintenance therapy with tacrolimus (TCL), and to apply the measurement of IMPDH activity to the therapeutic drug monitoring for mycophenolate mofetil (MMF).

METHODS

Eleven patients with renal transplants and 10 healthy volunteers were investigated. All patients were treated with a combination of TCL, steroid and MMF for 2 months after transplantation, and were in stable and good condition. IMPDH activity was determined indirectly by measuring xanthosine 5'-monophophate in cell lysates supplemented with IMP and beta-nicotine adenine dinucleotide using an high-performance liquid chromatography (HPLC) method.

RESULTS

The within-run reproducibility of the assay was excellent, with relative standard deviation (RSD) values of 0.41-4.08%. The mean differences between the spiked concentrations of xanthosine 5'-monophophate and their real values (mean relative errors; MREs) were within a range of 2.66-8.89%, showing good accuracy. The interday RSD values were 1.51-6.12% and MREs ranged from 2.10% to 8.89%. Cell lysates showed a 5-6 nmol/L IC(50) mycophenolic acid (MPA) concentration. TCL, cyclosporine and prednisolone did not affect IMPDH activity. The peak MPA concentration was achieved at 1 h after dosing. IMPDH activity decreased to 75% and 67% at 1 and 2 h after dosing respectively. Therefore, the inhibition rates of MPA against IMPDH activity may be adequate at 25-40% in TCL maintenance therapy.

CONCLUSION

Inosin-5'-monophosphate dehydrogenase activity in cell lysates could be reliably determined by HPLC. A 25-40% inhibition of IMPDH activity may be an appropriate range for preventing rejection with MPF but this requires further validation using larger studies with harder outcomes such as rejection episodes.

Correlation of IMPDH1 gene polymorphisms with subclinical acute rejection and mycophenolic acid exposure parameters on day 28 after renal transplantation

The risk of acute rejection in patients with higher exposure to mycophenolic acid (MPA), the active metabolite of mycophenolate mofetil (MMF), might be due to inosine 5'-monophosphate dehydrogenase (IMPDH) polymorphisms. The correlations with subclinical acute rejection, IMPDH1 polymorphisms and MPA exposure on day 28 post-transplantation were investigated in 82 Japanese recipients. Renal transplant recipients were given combination immunosuppressive therapy consisting of tacrolimus and 1.0, 1.5 or 2.0 g/day of MMF in equally divided doses every 12 hr at designated times. There were no significant differences in the incidence of subclinical acute rejection between IMPDH1 rs2278293 or rs2278294 polymorphisms (p = 0.243 and 0.735, respectively). However, in the high MPA night-time exposure range (AUC > 60 microg x h/ml and C(0 )> or = 1.9 microg/ml), there was a significant difference in the incidence of subclinical acute rejection between IMPDH1 rs2278293 A/A, A/G and G/G genotypes (each p = 0.019), but not the IMPDH1 rs2278294 genotype. In the higher daytime MPA exposure range, patients with the IMPDH1 rs2278293 G/G genotype also tended to develop subclinical acute rejection. In patients with the IMPDH rs2278293 A/A genotype, the risk of subclinical acute rejection episode tends to be low and the administration of MMF was effective. The risk of subclinical acute rejection for recipients who cannot adapt in therapeutic drug monitoring (TDM) of MPA seems to be influenced by IMPDH1 rs2278293 polymorphism. The prospective analysis of IMPDH1 rs2278293 polymorphism as well as monitoring of MPA plasma concentration after transplantation might help to improve MMF therapy.

Interpatient variability in IMPDH activity in MMF-treated renal transplant patients is correlated with IMPDH type II 3757T > C polymorphism

OBJECTIVES

The active metabolite of mycophenolate mofetil (MMF), mycophenolic acid, inhibits the activity of the target enzyme inosine monophosphate dehydrogenase (IMPDH). The aim of this study was to correlate eight different single nucleotide polymorphisms of the IMPDH type II gene to the activity of the IMPDH enzyme to explain between-patient differences in IMPDH activity.

METHODS AND RESULTS

In a prospective study, we measured IMPDH activity, mycophenolic acid plasma concentrations, and eight polymorphisms of IMPDH type II in de novo kidney transplant recipients, 6 days posttransplantation while on MMF treatment. Polymorphisms in the IMPDH type II gene were only observed for the IMPDH type II 3757T > C (rs11706052) single nucleotide polymorphism. Ten of 101 patients (10%) were heterozygous and two of 101 patients (2%) homozygous for IMPDH type II 3757T > C. The allele frequency was 6.9%. The IMPDH activity over 12 h (AUC(act)) was 49% higher for patients with an IMPDH type II 3757C variant [n = 12 vs. n = 68; 336 (95% confidence interval: 216-521) vs. 227 (95% confidence interval: 198-260) hmicromol/s/mol adenosine monophosphate; P = 0.04]. The IMPDH activity measured before transplantation (Act(pre-Tx)) was not significantly different between IMPDH type II 3757TT wild-type and variant carrier patients (P = 0.99).

CONCLUSION

We report that the IMPDH type II 3757T > C polymorphism is associated with an increased IMPDH activity in MMF-treated renal transplant patients. This polymorphism explains 8.0% of the interpatient variability in IMPDH activity.

Pharmacodynamic evaluation of the first dose of mycophenolate mofetil before kidney transplantation

BACKGROUND AND OBJECTIVES

The effect of mycophenolate mofetil (MMF) on T cell function has not been evaluated in patients undergoing kidney transplantation. The aim of this study was to assess the effect of 1g of MMF on T cell function, that is, intralymphocyte cytokine expression, T cell activation (CD25 and CD71), and T cell proliferation, as well as inosine monophosphate dehydrogenase (IMPDH) activity, to better understand the relationship between pharmacokinetic and pharmacodynamic markers in patients receiving the first dose of MMF before kidney transplantation.

PATIENTS

Twenty-four patients undergoing a kidney transplantation from a living donor were enrolled in this study.

RESULTS

Compared with baseline (before MMF intake), T cell proliferation (93%), IMPDH activity (74%), CD25 (46%), and CD71 (50%) expression significantly decreased during the first hour after MMF intake, in parallel to the rise in MPA concentration. Thereafter, all pharmacodynamic markers, except IMPDH activity, returned back to baseline level. There was a complex inverse relationship between pharmacokinetic and pharmacodynamic markers. The inhibition of T cell proliferation was highly correlated to IMPDH activity, but also to T cell activation markers.

CONCLUSION

The administration of MMF to patients is associated not only with a dramatic decrease in both T cell proliferation and IMPDH activity, but also with in a decrease in CD25 and CD71 expression.

Monitoring of inosine monophosphate dehydrogenase activity as a biomarker for mycophenolic acid effect: potential clinical implications

Mycophenolic acid (MPA) is a reversible inhibitor of inosine monophosphate dehydrogenase (IMPDH) and, in combination with other immunosuppressive drugs, effectively inhibits rejection in solid organ transplant recipients. MPA has a relatively narrow therapeutic window and exhibits wide inter- and intrapatient pharmacokinetic (PK) variability. This has stimulated the use of therapeutic drug monitoring as a strategy to tailor the MPA exposure to each patient's individual needs. Despite increasing therapeutic drug monitoring use, PK-assisted dosing is not universally adopted in part because of MPA's complex PK behavior. Targeting inosine monophosphate IMPDH activity as a surrogate pharmacodynamic (PD) marker of MPA-induced immunosuppression may allow for increased precision when used in an integrated PK-PD fashion, providing a more accurate assessment of efficacy and aid in limiting toxicity. IMPDH activity displays wide interpatient variability but relatively small intrapatient variability even after long-term administration of MPA. The advent of calcineurin and corticosteroid-sparing regimens necessitates more patient-specific PK-PD parameters, which can be used throughout the posttransplant period to optimize MPA exposure and immediate and long-term graft and patient outcomes. Quantification of IMPDH posttransplant may serve as a stable, surrogate PD marker of MPA-induced immunosuppression when combined with current PK and monitoring strategies.

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.

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.

Pharmacodynamics in the development of new immunosuppressive drugs

Over the past 10-20 years a number of immunosuppressive drugs, such as cyclosporine A, tacrolimus, sirolimus, or mycophenolate mofetil have been approved for clinical use and have been highly successful in preventing or delaying graft rejection. Nevertheless, there is an incessant need for better and safer drugs to improve short-term and long-term outcomes following transplantation. A number of low-molecular-weight molecules that interfere with immune cell functions are in development. These include molecules that inhibit the janus protein tyrosine kinase JAK3, compounds that alter lymphocyte trafficking (the sphingosine-1-phosphate receptor antagonist FTY720), and new malononitrilamides (FK778). All seem to show promising therapeutic potential. Among the biologic agents, there are high expectations for antibodies or recombinant chimeric molecules targeting costimulatory surface molecules or pathways involved in the migration of immune cells. The list of such targets includes the ligand pairs CD28:B7, CD154:CD40, LFA-1:ICAM-1, ICOS:B7RP-1, and VLA-4:VCAM-1. However, the clinical development of drugs for transplantation has proved to be difficult, complex, and time consuming. Therefore, newly emerging drug candidates will also demand better methods for monitoring their efficacy as well as their side effects in vivo. Pharmacokinetics (PK) and pharmacodynamics (PD) are complementary approaches used to select drugs on the basis of their in vivo efficacy as well as safety. Whereas PK monitors the handling of the drug by the body, PD focuses on the biologic effect of the drug on its target. Therefore, PD studies of in vivo efficacy are useful for clinical decisions to determine the optimal dose and type of immunosuppressant. At the preclinical stage, PD is aimed at accelerating the selection of lead compounds via PD-controlled trials in animals. Moreover, PD can help to discover new mechanisms of action for a drug or a drug candidate. However, its full potential has not been used, mainly because of laborious and time-consuming methodology. This review focuses on established and novel PD/PK approaches to assess immunosuppressive compounds in the context of new evolving drugs or drug combinations.

From Mechanisms to Long-Term Benefits

Mycophenolate mofetil (MMF), a widely used immunosuppressant in solid organ transplantation, is a prodrug to deliver mycophenolic acid (MPA). MMF has been shown to decrease rejection rates and to improve graft survival, and probably accomplishes this through a variety of mechanisms. Its most prominent mechanism is to inhibit lymphocyte proliferation by inhibition of inosine monophosphate dehydrogenase. However, just as important to its overall beneficial effects are other mechanisms that include inhibition of proliferation of smooth muscle and fibroblasts, inhibition of antibody production, inhibition of lymphocyte adhesion and migration, and inhibition of nitric oxide synthase.

The need of mycophenolic acid monitoring in long-term renal transplants

BACKGROUND

There is little information regarding the 12-h mycophenolic acid (MPA) pharmacokinetics (PK), a way to monitor the drug and the need of frequent monitoring, in stable patients.

METHODS

A cohort of 35 adults, under long-term mycophenolate mofetil (MMF) therapy plus cyclosporin A (n = 12), TACimus (n = 12) or MMF only (n = 11); all with prednisone had a 12-h MPA-PK performed to ascertain the percentage of them within a defined therapeutic window. In 13 other patients, two PK studies undergone 1 wk apart were performed to evaluate the need for frequent measurements.

RESULTS

Fourteen (40%) patients were within the defined therapeutic window (36-60 microg h/mL). Nine patients (26%) were overexposed while 12 (34%) were underexposed. A Cmax> or =10 microg/mL was seen in 20 (57%) of the patients. These percentages were equally distributed between the treatment groups both for AUC0-12 and Cmax. The equations using C0, C2 or both predict exposure, although the use of C2 seems to be more adequate in clinical practice. There were no differences in MPA exposure in patients with a repeated PK evaluated 1 wk later.

CONCLUSION

The use of MMF without monitoring MPA blood levels may cause over-/underexposure to the drug in stable recipients. However, in patients under MMF for more than 1 yr, MPA levels are stable and there is no need for frequent measurements.

Simple reversed-phase ion-pair liquid chromatography assay for the simultaneous determination of mycophenolic acid and its glucuronide metabolite in human plasma and urine

A simple and reproducible reversed-phase ion-pair high-performance liquid chromatographic (HPLC) method using isocratic elution with UV absorbance detection is presented for the simultaneous quantitation of mycophenolic acid (MPA) and MPA-glucuronide (MPAG) in human plasma and urine. The sample preparation procedures involved simple protein precipitation for plasma and 10-fold dilution for urine. Each analytical run was completed within 15min, with MPAG and MPA being eluted at 3.8 and 11.4min, respectively. The optimized method showed good performance in terms of specificity, linearity, detection and quantitation limits, precision and accuracy. This assay was demonstrated to be applicable for clinical pharmacokinetic studies.