A retrospective analysis of mycophenolic acid and cyclosporin concentrations with acute rejection in renal transplant recipients

Nonperturbative Fluorogenic Labeling of Immunophilins Enables the Wash-free Detection of Immunosuppressants

Immunosuppressants are clinically approved drugs to treat the potential rejection of transplanted organs and require frequent monitoring due to their narrow therapeutic window. Immunophilins are small proteins that bind immunosuppressants with high affinity, yet there are no examples of fluorogenic immunophilins and their potential application as optical biosensors for immunosuppressive drugs in clinical biosamples. In the present work, we designed novel diazonium BODIPY salts for the site-specific labeling of tyrosine residues in peptides via solid-phase synthesis as well as for late-stage functionalization of whole recombinant proteins. After the optimization of a straightforward one-step labeling procedure for immunophilins PPIA and FKBP12, we demonstrated the application of a fluorogenic analogue of FKBP12 for the selective detection of the immunosuppressant drug tacrolimus, including experiments in urine samples from patients with functioning renal transplants. This chemical methodology opens new avenues to rationally design wash-free immunophilin-based biosensors for rapid therapeutic drug monitoring.

Integrative analysis of purine metabolites and gut microbiota in patients with neuromyelitis optica spectrum disorders after mycophenolate mofetil treatment

BACKGROUND

Neuromyelitis optica spectrum disorder (NMOSD) is a recurring inflammatory demyelinating disease that is commonly observed in Asian countries like China. Prior investigations have shown that mycophenolate mofetil (MMF) with better biocompatibility compared to azathioprine (AZA), and can prevent relapses of NMOSD, but the efficacy was controversially reported in different NMOSD cases. We aimed to explore the factors that weaken efficacy of MMF in NMOSD.

METHODS

A total of 34 NMOSD patients treated with MMF were prospectively enrolled and grouped according to the therapeutic efficacy as effective group (EG, n = 23) versus less-effective group (LEG, n = 11). The purine metabolites were profiled in serum samples and gut microbiota was analyzed using 16S rRNA sequencing with stool samples from the same patients.

RESULTS

Purine salvage pathway (PSP) metabolites (inosine, hypoxanthine, xanthine, guanine and uric acid) in the serum of NMOSD patients were elevated in the LEG compared to EG (p < 0.05). Additionally, the richness and microbial diversity of gut microbiota was found to be similar between EG and LEG patients. However, LEG patients had increased presence of Clostridium and Synergistes but decreased abundance of the Coprococcus genus.

CONCLUSIONS

The PSP metabolites and composition of the gut microbiota were changed between patients with or without optimal clinical response after MMF treatment. This may help us to understand the pharmacodynamics of MMF in NMOSD.

Optimizing Mycophenolic Acid Exposure in Kidney Transplant Recipients: Time for Target Concentration Intervention

The immunosuppressive agent mycophenolate is used extensively in kidney transplantation, yet dosing strategy applied varies markedly from fixed dosing ("one-dose-fits-all"), to mycophenolic acid (MPA) trough concentration monitoring, to dose optimization to an MPA exposure target (as area under the concentration-time curve [MPA AUC0-12]). This relates in part to inconsistent results in prospective trials of concentration-controlled dosing (CCD). In this review, the totality of evidence supporting mycophenolate CCD is examined: pharmacological characteristics, observational data linking exposure to efficacy and toxicities, and randomized controlled trials of CCD, with attention to dose optimization method and exposure achieved. Fixed dosing of mycophenolate consistently leads to underexposure associated with rejection, as well as overexposure associated with toxicities. When CCD is driven by pharmacokinetic calculation to a target concentration (target concentration intervention), MPA exposure is successfully controlled and clinical benefits are seen. There remains a need for consensus on practical aspects of mycophenolate target concentration intervention in contemporary tacrolimus-containing regimens and future research to define maintenance phase exposure targets. However, given ongoing consequences of both overimmunosuppression and underimmunosuppression in kidney transplantation, impacting short- and long-term outcomes, these should be a priority. The imprecise "one-dose-fits-all" approach should be replaced by the clinically proven MPA target concentration strategy.

RELATE: Relationship of limited sampling strategy and adverse effects of mycophenolate mofetil in pediatric renal transplant patients

MMF, a prodrug converted to the active form MPA, is an immunosuppressant used to prevent rejection in solid organ transplant recipients. MPA exposure, defined by AUC, can be estimated using limited sampling strategies (LSS). The relationship between MPA AUC and clinical outcomes has not been studied in pediatrics. The objectives were to describe the relationship of MPA AUC (estimated via LSS) with adverse effects and rates of rejection, and to compare clinical outcomes between different MPA monitoring practices. Descriptive statistics were used to summarize demographics, adverse effects, and rejection. Thirty-three patients (91 trough concentrations and 12 LSS sets) aged 2-20 years old were included. The estimated median MPA AUCs (David-Neto and Filler) were higher for those who did not have any adverse effects reported (65.85 and 85.05 mg*h/L, respectively) compared to those who had an adverse effect (60.75 and 54.2 mg*h/L, respectively). The median trough concentration when no adverse effects occurred was comparable to when adverse effects occurred. The median MPA AUC at which rejection occurred was lower than in those without rejection. The median trough concentration at which rejection occurred was higher than those without rejection (3.1 mg/L compared to 1.9 mg/L). The occurrence of adverse effects or rejection was not shown to be related to measured MPA trough or AUC outside of the target therapeutic range. The value of MPA concentration monitoring remains unclear; therefore, the practice of monitoring MPA AUC by LSS or trough concentrations should be reconsidered.

Impact of intensive dosing of mycophenolate on pancreas allograft survival

PURPOSE

To evaluate the effect of mycophenolate (mycophenolic acid, MPA) dose on pancreas allograft survival following simultaneous pancreas kidney (SPK) transplant.

METHODS

This was an observational study of adult SPK recipients transplanted between 1/1/2002 and 6/30/2015. Recipients were divided into cohorts based on MPA dose at discharge: high dose (HD), 1000 mg three times daily mycophenolate mofetil (MMF) and standard dose (SD), 1000 mg twice daily MMF. Primary outcome was pancreas allograft survival. Secondary endpoints included kidney allograft survival, pancreas allograft rejection, infection, time to initial dose decrease, and patient survival (PS).

RESULTS

In all, 453 patients met inclusion criteria: 324 in HD-MPA group and 129 in SD-MPA group. HD-MPA patients had higher rates of pancreas graft survival (P = .003). There were no differences in rates of pancreas allograft rejection (P = .8), kidney graft survival (P = .15), overall infection (P = .4), overall malignancy (P = .93), time to first dose reduction (P = .35), or patient survival (P = .3). In a multivariable analysis adjusted for differences between groups and known confounders, dosing group continued to significantly affect incidence of pancreas allograft failure (P = .02).

CONCLUSIONS

HD-MPA significantly impacted pancreas allograft survival in SPK recipients independent of graft rejection. Further studies are warranted to investigate the etiology of this finding and determine the optimal duration of HD-MPA associated with positive graft outcomes.

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.

High interpatient variability in response to mycophenolic acid maintenance therapy in patients with ANCA-associated vasculitis

BACKGROUND

Mycophenolic acid (MPA) is used in the maintenance therapy of antineutrophil cytoplasm antibody-associated systemic vasculitis (AASV). MPA exerts its immunosuppression by inhibiting inosine 5'-monophosphate dehydrogenase (IMPDH), depleting activated lymphocytes of guanine nucleotides and retarding their proliferation. The purpose of our study was to examine the correlation between clinical outcome and pharmacokinetic-pharmacodynamic (PD) relationships of MPA in patients with AASV.

METHODS

We studied 358 Caucasian control patients without any MPA therapy to examine basal IMPDH activity. Thirty Caucasian patients with AASV under maintenance therapy with mycophenolate mofetil (MMF) underwent therapeutic drug monitoring.

RESULTS

We observed a high interindividual variability with regard to basal IMPDH activity in patients without any MPA treatment (0.8-35 nmol/mg protein/h). Patients were followed for a mean (±SD) period of 22 ± 8 months. During the observation period, seven patients had a relapse with an elevated Birmingham Vasculitis Activity Score of 9.2 ± 6. The basal IMPDH activity (Abasal) in patients who subsequently relapsed was raised at baseline, before receiving their first dose of MMF, and further increased at the time of relapse, when compared with stable patients. Patients with a relapse during the maintenance therapy had significantly higher levels of IMPDH activity [IMPDH enzyme activity curve (AEC) (0-12)] than stable patients (P = 0.001), indicating inadequate IMPDH suppression. MPA-AUC (0-12) was significantly decreased in relapse patients, in contrast to stable patients (P < 0.05).

CONCLUSIONS

Due to the highly variable response to maintenance therapy with MPA, PD drug monitoring is a new tool for detecting inadequate immunosuppression in AASV patients.

Genetic polymorphisms of UGT1A8, UGT1A9 and HNF-1α and gastrointestinal symptoms in renal transplant recipients taking mycophenolic acid

Mycophenolic acid (MPA), a widely used immunosuppressant, has a complex metabolism that involves a number of enzymes. Some of its metabolites are thought to be the cause of gastrointestinal (GI) side effects. In this study, we investigated whether polymorphisms of UDP-glucuronosyltransferases (UGT1) A8, 1A9, and hepatocyte nuclear factor (HNF1α) genes or pharmacokinetic parameters of mycophenolic acid (MPA) were associated with the severity of GI symptoms in patients receiving MPA therapy. A total of 109 kidney transplant patients taking mycophenolic acid (MPA) derivatives were genotyped for UGT1A8, 1A9 and HNF1α genes. Among these, a total of 15 patients were participants in the pharmacokinetic study. Severity of GI symptoms was assessed using a validated Gastrointestinal Symptom Rating Scale (GSRS). The overall and subscale GSRS scores were measured at 1 week (baseline), 2 weeks, 3 months and 6 months post-transplantation. In the case of the pharmacokinetic study, EC-MPS was administered and a total of nine blood samples were obtained at -1, 0, 0.5, 1, 2, 4, 6, 8, and 12h. Genotypes of UGT1A8 were significantly associated with the overall GSRS scores at week 1 (p=0.02) and week 2 (p=0.036). Subscales were only statistically significant for constipation at week 1 (p=0.002) and indigestion at week 2 (p=0.02), while UGT1A9 was only significant for the constipation at week 1 (p=0.04). HNF1α genotypes were significantly different at week 1 in the overall GSRS (p=0.004), and for abdominal pain (p=0.04), acid reflux (p=0.036) and constipation subscales (p=0.04). In addition, abdominal pain was statistically significantly different at 3 months and 6 months after transplantation (p=0.03 and 0.02, respectively). In the case of the pharmacokinetic study, we have found some correlations between MPAC0 and constipation (p=0.02) where MPAAUC was correlated with acid reflux (p=0.02) and constipation (p=0.012), MPAGCL/F was correlated to acid reflux, indigestion, constipation and the sum of the GSRS scores (p=0.037, p=0.032, p=0.033 and p=0.04, respectively). Multinomial regression analysis for MPAGCL/F showed a statistical significance for the subscale indigestion and the sum of the GSRS (p=0.033 and p=0.037, respectively). Our data suggests that among patients receiving MPA the UGT1A9 alleles might play a role in determining the severity of early GI side effects, while the HNF1α allele appears to be associated with a later effect as well as early side effects. Our data also showed that some kinetic parameters might predict MPA side effects.

Cyclosporine alters correlation between free and total mycophenolic acid in kidney transplant recipients in the initial phase

WHAT IS KNOWN AND OBJECTIVE

The factors affecting the pharmacokinetics of free mycophenolic acid (MPA) and its phenolic glucuronide (MPAG) are still unclear. The aim of this study was to evaluate the influence of cyclosporine on the pharmacokinetics of free MPA and MPAG.

METHODS

Seventy-seven kidney transplant recipients (23 were in an initial phase and 54 in a stable phase; 41 were treated with cyclosporine and 36 with tacrolimus) were enrolled. Free and total MPA and MPAG were determined using HPLC. The correlations between free and total predose concentrations (C(0) ) of MPA or MPAG were evaluated separately in patients receiving calcineurin inhibitor medications.

RESULTS AND DISCUSSION

Serum concentration of albumin was lower in the initial phase than in the stable phase. A higher ratio of free MPAG C(0) to free MPA C(0) was observed in cyclosporine-treated than tacrolimus-treated kidney transplant recipients. Free MPA C(0) correlated weakly with total MPA C(0) in kidney transplant recipients treated with cyclosporine in the initial phase (ρ= 0·53, P = 0·06).

WHAT IS NEW AND CONCLUSION

Cyclosporine increased the ratio of free MPAG C(0) to free MPA C(0) and varied the free fraction of MPA in the hypoalbuminaemic kidney transplant recipients in the initial phase.

The influence of pharmacogenetics and cofactors on clinical outcomes in kidney transplantation

INTRODUCTION

Immunosuppressive drugs have a narrow therapeutic range and large inter-individual response variability. This has prompted pharmacogenetic studies, mostly with regard to their dose-concentration relationships, but also about proteins involved in their pharmacodynamics. Some polymorphisms of genes involved in their disposition pathways were shown to affect their dose-concentration relationships. The impact of pharmacogenetics on tissue distribution and the resulting clinical effects have less often been studied. More importantly, a few single nucleotide polymorphisms seem to have a significant impact on the incidence of acute rejection or the adverse effects of immunosuppressants. Environmental factors often interact with such genotype-phenotype relationships.

AREAS COVERED

This article reviews the impact of genetic polymorphisms of the metabolic enzymes, membrane transporters and target proteins of mycophenolic acid, calcineurin inhibitors and mammalian target of rapamycin inhibitors on clinical outcomes in kidney transplantation.

EXPERT OPINION

The current level of evidence is not yet high enough to recommend pharmacogenetic personalization of immunosuppressive regimens in transplant recipients. The prevention of cellular toxicity associated with local metabolism or transport, which cannot be addressed by routine monitoring, is worth investigating further.

Population pharmacokinetics of mycophenolic acid and metabolites in patients with glomerulonephritis

Mycophenolic acid (MPA) is an inosine monophosphate dehydrogenase inhibitor used for glomerulonephritis treatment. The objective of the current study was to develop a population pharmacokinetic model for MPA and metabolites in glomerulonephritis to enable appropriate design of MPA regimens in these patients with alterations in kidney structure and function. Thirty-nine patients with glomerulonephritis and receiving mycophenolate mofetil were recruited to participate in a 24-hour pharmacokinetic study. Blood was collected at times 0, 0.5, 1.0, 1.5, 2, 3, 4, 6, 8, 12, and 24 hours and urine was collected over the intervals of 0 to 6, 6 to 12, and 12 to 24 hours. Plasma and urine samples were assayed for MPA and MPA glucuronide (MPAG) by high-performance liquid chromatography and for acyl-MPA glucuronide (AcMPAG) by liquid chromatography/mass spectrometry. Population pharmacokinetic analysis and covariate model building were evaluated using Non-linear Mixed Effect Modeling software (NONMEM, Version 6.2.0; ICON Development Solutions, Ellicott City, MD). The final model for MPA and its metabolites consisted of nine discrete compartments; 1) depot gastrointestinal; 2) central MPA; 3) peripheral MPA; 4) gallbladder; 5) MPA urine; 6) MPAG central; 7) MPAG urine; 8) AcMPAG central; and 9) AcMPAG urine compartment. The MPA population mean estimates for apparent nonrenal clearance (ClNR/F) and apparent central volume of distribution were 14.3 L/hr and 21.1 L, respectively. The mean population estimate for apparent renal clearance (ClR/F) was dependent on estimated creatinine clearances (eClcr); 0.0975 L/hr for eClcr 80 mL/min or less and 0.157 L/hr for eClcr greater than 80 mL/min. Covariate analyses identified: eClcr on CLNR,MPA/F (P < 0.001), eClcr (with a cutoff value at 80 mL/min) on CLR,MPA/F (P < 0.025), serum albumin on CLNR,MPA/F (P < 0.01), eClcr on CLR,MPAG/F (P < 0.001), and eClcr on CLR,AcMPAG/F (P < 0.001). Evaluation of the final model by visual predictive check showed that most of the observed values were within the 95th percent prediction interval generated from 100 simulations of the final model. The current population pharmacokinetic model demonstrated eClcr and serum albumin influenced the renal and nonrenal components of Cl/F, suggesting patients with glomerulonephritis would have highly altered MPA exposures.

Pharmacokinetics of mycophenolic acid in severe lupus nephritis

Mycophenolic acid (MPA) is an effective treatment for active lupus nephritis despite its variable efficacy in different ethnic groups. Here we tested whether pharmacokinetic monitoring may help to optimize dosing of MPA in an Asian population. Patients with biopsy-proven class III or IV lupus nephritis (ISN/RPS category) were treated with mycophenolate mofetil or enteric-coated mycophenolate sodium. One month after initiating treatment we measured plasma MPA levels in eight samples taken over a 12-h period after drug administration. The mean area under the time-dependent curve for MPA of responding patients was significantly higher than those not responding. Successful treatment was seen in patients with areas >45 mg h/l. The dosage of the drug was not related to MPA pharmacokinetics. In the mycophenolate mofetil group, however, MPA-area under the curve was positively, and significantly, correlated with trough or 1 h after dose concentrations and associated with a therapeutic response. Thus, our study shows that MPA pharmacokinetics were positively correlated with therapeutic responses of mycophenolate, suggesting that controlling the concentrations may improve its therapeutic efficacy in lupus nephritis. As the absorption and pharmacokinetic peak of enteric-coated tablets is slower, it is important to take different formulations into account when determining optimal MPA concentrations.

Population pharmacokinetics of mycophenolic acid and its 2 glucuronidated metabolites in kidney transplant recipients

The population pharmacokinetics of mycophenolic acid (MPA) and its phenolic (MPAG) and acyl (AcMPAG) glucuronide metabolites were studied in patients taking enteric-coated mycophenolate sodium. Plasma samples (n = 232), obtained from 18 renal transplant recipients, were analyzed for MPA, MPAG, and AcMPAG using a validated high-performance liquid chromatography/ultraviolet assay. Population pharmacokinetic analysis was performed using NONMEM. The pharmacokinetics of MPA were best described by a 2-compartment model, with MPAG and AcMPAG produced from the central compartment and with enterohepatic recirculation of MPA via these 2 metabolites. Population mean estimates for MPA were apparent clearance (CL/F) of 10.6 L/h (interindividual variability [IIV] = 21.4%) and apparent volume of distribution of the central compartment (V(1)/F) of 25.9 L (IIV = 87.8%). Mean elimination rate constants of MPAG and AcMPAG were 0.323 h(-1) (IIV = 29.1%) and 0.206 h(-1) (IIV = 48.8%), respectively. The mean fraction of MPA converted to MPAG and AcMPAG, normalized by their volumes of distribution (FM(AG) and FM(AC), respectively), was also estimated. The elimination rate constant for MPAG and FM(AC) was influenced by glomerular filtration rate in patients with renal impairment. The visual predictive check, based on 100 simulated data sets each for MPA, MPAG, and AcMPAG, found that the final pharmacokinetic model adequately predicts the observed concentrations of all 3 species.

A limited sampling strategy for estimating mycophenolic acid area under the curve in adult heart transplant patients treated with concomitant cyclosporine

OBJECTIVE

Heart transplantation studies have shown a relationship between the mycophenolic acid area under the curve (AUC) 0-12 h (MPA AUC(0-12h)) values and risk of acute rejection episodes and fewer side-effects in patient receiving cyclosporine during the first year post-transplant. However, measurement of full AUC is costly and time consuming and in this case it is an impractical approach to drug monitoring. Therefore, the authors describe a limited sampling strategy to estimate the MPA AUC(0-12h) value in adult heart transplant recipients.

METHODS

Ninety MPA pharmacokinetic (PK) profiles were studied. The samples were collected immediately before and 0.5, 1, 1.5, 2, 2.5, 3, 4, 6, 9, 12 h after the morning dose of mycophenolate mofetil (MMF) following an overnight fast. PK profiles were determined at 6-8 weeks, 6, 12 months and more than 1 year after transplantation. Using stepwise multiple linear regression analysis a sampling strategy from 60 of PK profiles was obtained and next the bias and precision of the model were evaluated in another 30 PK profiles.

RESULTS

The three-point model using C(0.5h), C(1h), C(2h) was found to be superior to all other models tested (r(2) = 0.841). The regression equation for AUC estimation which gave the best fit to this model is: 9.69 + 0.63C(0.5) + 0.61C(1) + 2.20C(2). Using that model 63 of the 90 (70%) full AUC values were estimated within 15% of their actual value. For the best-fit model, the mean prediction error was 3.2%, with 95% confidence intervals for prediction error to range from -42.2% to 40.3%. All other models which use one, two or three time-points over the first 2 h are poorer predictors of the full AUC than the model above.

CONCLUSION

The proposed three time-point equation to estimate AUC will be helpful in optimizing immunosuppressive therapy in heart transplantation.

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.

Lack of an Effect of Oral Iron Administration on Mycophenolic Acid Pharmacokinetics in Stable Renal Transplant Recipients

STUDY OBJECTIVES

To determine if coadministration of polysaccharide iron complex and slow-release ferrous sulfate alter the absorption of mycophenolic acid (MPA), and to examine the potential influence of dosing relative to mycophenolate mofetil (MMF) administration and the effect of immediate- versus sustained-release iron products on the steady-state pharmacokinetics of MPA.

DESIGN

Prospective, open-label, three-phase, crossover, steady-state pharmacokinetic study.

SETTING

National Institutes of Health-sponsored General Clinical Research Center at a university medical center.

PATIENTS

Twelve adult (mean age 50 yrs) renal transplant recipients who were receiving concomitant iron and MMF maintenance therapy.

INTERVENTION

Oral iron therapy was coadministered with MMF on days -6-0, MMF was administered alone on days 1-8 (control phase), then oral iron therapy was administered 2 hours after MMF administration on days 9-16.

MEASUREMENTS AND MAIN RESULTS

Baseline demographics, concurrent drug regimens, and clinical laboratory values were assessed. Blood samples were obtained at baseline and at 1, 2, 3, 4, 6, 8, and 12 hours after MMF administration on days 0, 8, and 16. The MPA levels were measured by high-performance liquid chromatography. We found no significant differences in the dose-standardized area under the concentration-time curve from 0-12 hours (AUC(0-12)) for MPA between the control phase (39.66 +/- 8.70 mg mg x hr/L) and the concomitant ferrous sulfate or dose-separated ferrous sulfate (37.56 +/- 9.95 or 32.84 +/- 8.43 mg x hr/L, respectively, p>0.05) phases. Dose-standardized AUC(0-12) values for MPA did not significantly differ after the concomitant administration of polysaccharide iron complex from that of the control phase (48.46 +/- 9.68 and 43.80 +/- 9.46 mg x hr/L, respectively, p=0.065). However, the AUC(0-12) for MPA significantly increased when polysaccharide iron complex was administered 2 hours after MMF (53.41 +/- 11.75 mg x hr/L, p=0.012). Maximum concentrations and times to reach maximum concentrations remained consistent across all study phases in each arm of the trial (p>0.05).

CONCLUSION

Multiple doses of iron therapy-slow-release ferrous sulfate, or polysaccharide iron complex-did not significantly reduce systemic exposure to MMF, as measured by using AUC(0-12) values.

Individualization of mycophenolate mofetil dose in renal transplant recipients

The immunosuppressive agent mycophenolate mofetil has been successfully used over the past 10 years to prevent acute allograft rejection after renal transplantation. It has mainly been administered as a fixed dose of mycophenolate mofetil 1000 mg b.i.d. The pharmacokinetics of mycophenolic acid, the active moiety of the prodrug mycophenolate mofetil, show large between-patient variability, and exposure to mycophenolic acid correlates with the risk for acute rejection. This suggests that already excellent clinical results can be further improved by mycophenolate mofetil dose individualization. This review discusses different arguments in favour of individualization of mycophenolate mofetil dose, as well as strategies for managing mycophenolate mofetil therapy individualization, including pharmacokinetic and pharmacodynamic monitoring and dose individualization based on pharmacogenetic information. It is expected that pharmacokinetic monitoring of mycophenolic acid will offer the most effective and feasible tool for mycophenolate mofetil dose individualization.

A comparison of the effect of ciclosporin and sirolimus on the pharmokinetics of mycophenolate in renal transplant patients

AIM

To compare the pharmacokinetics of mycophenolic acid when given with either ciclosporin or sirolimus, and investigate in vitro the potential effect of ciclosporin, sirolimus, tacrolimus and everolimus on mycophenolic acid metabolism.

METHODS

In renal transplant patients given mycophenolate mofetil in combination with ciclosporin (n = 19) or sirolimus (n = 12), concentration-time profiles of mycophenolic acid, mycophenolic-acid-phenyl-glucuronide, mycophenolic-acid-acyl-glucuronide and mycophenolic-acid-phenyl-glucoside were determined at one month post-transplant. The effect of immunosuppressive drugs on mycophenolic acid glucuronidation and glycosylation was investigated in vitro using human liver microsomes.

RESULTS

The mean mycophenolic acid AUC(0-9 h) in the sirolimus group was 44.9 mg h(-1) L(-1) (95% CI: 34.7-55.1), vs. 30.5 mg h(-1) L(-1) (95% CI: 25.4-35.6) in the ciclosporin group, corresponding to 1.5-fold dose-normalized difference (95% CI: 1.1-1.9; P < 0.05). In addition, the metabolite/mycophenolic acid AUC(0-9 h) ratios were significantly higher in patients cotreated with ciclosporin than with sirolimus, giving values of 1.8-fold (95% CI: 1.3-2.3; P = 0.0009), 2.6-fold (95% CI: 2.0-3.3; P < 0.0001) and 4.3-fold (95% CI: 2.6-6.0; P = 0.0016) for mycophenolic-acid-phenyl-glucuronide, mycophenolic-acid-acyl-glucuronide and mycophenolic-acid-phenyl-glucoside, respectively. In vitro, none of the immunosuppressive drugs tested inhibited mycophenolic acid metabolism.

CONCLUSION

Patients taking mycophenolate mofetil and sirolimus experience a higher exposure to mycophenolic acid and a lower exposure to mycophenolic acid metabolites than those being treated with mycophenolate mofetil and ciclosporin. This interaction is probably not caused by inhibition of mycophenolic acid glucuronidation or glycosylation, but is more likely to be due to the influence of ciclosporin on the excretion of mycophenolic acid metabolites into bile.

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.

Quantification and 24-hour monitoring of mycophenolic acid by high-performance liquid chromatography in Japanese renal transplant recipients

We developed a rapid, simple, and sensitive high-performance liquid chromatography method with UV detection for the quantitative determination of mycophenolic acid (MPA) in human plasma. MPA and the internal standard (naproxen) were separated using a mobile phase of 0.04 M H(3)PO(4)-acetonitrile-methanol (3:3:4 v/v/v) over a CAPCELL PAK C18 MG column. A flow-rate of 0.5 ml/min was used at ambient temperature and sample detection was carried out at 254 nm. The assay required only 100 microl of plasma and involved liquid-liquid extraction, which gave high recovery (>94%). The lower limit of quantification for MPA was 0.05 microg/ml. Inter- and intra-day coefficients of variation were less than 9.6% and accuracies were within 9.3%. Additionally, we validated this method in 24-hour monitoring of plasma MPA concentrations after mycophenolate mofetil (MMF) morning and evening administration in 40 Japanese renal transplant recipients with 1.5 g/day MMF. The time to reach the maximum (11.7 microg/ml) and second peak (4.5 microg/ml) of MPA after morning 0.75 g MMF administration was 2.6 h and 9.0 h, and time to reach maximum (10.5 microg/ml) after evening 0.75 g administration was 4.0 h.

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.

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.

CEDIA® Mycophenolic Acid Assay Compared With HPLC-UV in Specimens From Transplant Recipients

Routine monitoring of mycophenolic acid (MPA) has been accepted as an essential tool in the management of this therapy in transplant recipients. The availability of simple, sensitive assays that measure MPA in plasma permits individualization of dosing regimens according to pharmacokinetic principles. We report the results of an evaluation of the CEDIA Mycophenolic Acid Immunoassay (Microgenics Corporation, Fremont, California) for the measurement of plasma MPA concentrations in a range of transplant indications and compare its performance and specificity to an established HPLC/UV method. Precision and accuracy were determined both within and between runs using the quality control materials provided with the CEDIA MPA assay, which produced within run (n = 21) coefficients of variation (CV%) and biases of less than 5%. The between run analyses, performed over consecutive days following daily calibration of the assay, showed CVs and biases of less than 7%. Routine patient samples (n = 298) from 142 patients of varying transplant type were analyzed using the CEDIA MPA kit and HPLC/UV methods. Regression analysis of the patient samples gave an equation of CEDIA = 1.18 HPLC/UV + 0.45 (r = 0.83). According to the manufacturer's product information, there is 192% cross reactivity with the active mycophenolate acyl glucuronide. The data presented suggest that the CEDIA MPA immunoassay, run on the Hitachi 911 analyzer, over-estimates plasma MPA concentrations with a magnitude that is influenced by transplant type. Hence, users must interpret the immunoassay results with caution and not assume that the metabolite fraction is constant in recipients of the same organ type or in different organ transplant populations.

Comparison of mycophenolic acid pharmacokinetic parameters in kidney transplant patients within the first 3 months post-transplant

OBJECTIVE

The aim of this study was to investigate the effect of time on pharmacokinetic (PK) parameters of mycophenolic acid (MPA) in the early post-transplant period in kidney recipients. MPA is the active metabolite of mycophenolate mofetil (MMF), which was introduced into clinical practice ten years ago.

METHOD

Mycophenolate mofetil was co-administered with cyclosporin (CsA) in a subgroup of 23 patients and with tacrolimus (Tac) in a subgroup of 10 patients. MPA plasma concentration profiles were measured by a validated high performance liquid chromatography method 1 week, 2 and 3 months after transplantation.

RESULTS

Despite a comparable MMF dose, a large inter-patient variability in both MPA area under the curve (AUC) from 0 to 12 h (range 10.03-135.4 microg h/mL) and in predose concentrations (0.31-6.09 microg/mL) was observed. Patients with AUC > 35 microg h/mL showed better (P < 0.1) renal function than patients with AUC < 20 microg h/mL (mean creatinine concentration 1.48 +/- 0.12 vs. 3.35 +/- 0.4 mg/dL respectively). The total MPA trough and AUC did not correlate with biochemical parameters: leucocyte cell count and haematocrit. A higher trough level of the metabolite MPA glucuronide (MPAG) in the 1 week after transplantation was found when compared with the 3-month level (mean 150.1 +/- 146.7; range 17.1 to 560 vs. 75.8 +/- 40.0; range 27.3 to 174.2 microg/mL). The concentration of MPA, and MPA AUC values were significantly lower in patients receiving MMF and CsA than those receiving MMF and Tac during all three periods studied (P < 0.02). The influence of C(0) and MPA AUC values on the risk of graft rejection was investigated using receiver operating characteristic (ROC) curve analysis. The area under the ROC curve for AUC was 0.847, whereas that of C(0) was 0.632.

CONCLUSIONS

The MPA AUC(0-12h) appeared to be the more effective PK parameter for predicting acute rejection. We recommend that routine MPA and MPAG therapeutic drug level monitoring should be an important part of MMF therapy.

Mycophenolic acid 12-h trough level monitoring in renal transplantation: association with acute rejection and toxicity

Studies of renal transplantation utilizing trough plasma level monitoring of mycophenolic acid (MPA) have shown inconsistent associations with toxicity and rejection. In this study, 5600 12-h trough MPA samples from 121 renal transplant recipients immunosuppressed with mycophenolate mofetil (MMF) and tacrolimus in a steroid sparing protocol (steroids for 7 days only) were sequentially analyzed. Higher MPA levels were associated with lower hemoglobin concentrations and anemia (hemoglobin <10 g/dL). Similarly, higher MPA levels were associated with lower total white cell counts and an increased incidence of leucopenia (total white cell count <4.0 x 10(9)/L). Hypoalbuminemia and renal impairment were also associated with hemotoxicity. MMF-associated diarrhea and viral infection were associated with higher MPA levels. Conversely, biopsy-proven acute rejection within the first month post-transplantation was associated with lower MPA levels. Anti-CD25 antibody induction was also associated with reduced rejection rates. No association was seen between MPA levels and platelet count, thrombocytopenia or bacterial infection. An MPA level of 1.60 mg/L early post-transplantation best discriminated patients with and without rejection, and an MPA level of 2.75 mg/L best discriminated patients with and without toxicity later post-transplantation.

Mycophenolic acid clinical pharmacokinetics influenced by a cyclosporine C2 based immunosuppressive regimen in renal allograft recipients

Therapeutic drug monitoring of mycophenolic acid (MPA) in combination with cyclosporine 2-h concentration (CsA C2, n = 68) or tacrolimus trough concentration (n = 10) was investigated by repeated measurements of MPA and MPA-glucuronide (MPAG) trough concentrations in renal allograft recipients during the first 3 months post-transplant. The acute rejection rate was lower (19% vs. 43%; P < 0.05) in patients achieving CsA C2 target range during the first week (1600-2000 microg/l), n = 26, compared with those who did not, n = 42. Median MPA concentration was 0.9 and 1.2 microg/ml in patients within or below C2 range, respectively (P = 0.19). CsA C2 correlated with MPAG-to-MPA ratio (P < 0.01, r = 0.91) and gamma-glutamyl-transpeptidase (GGT, P < 0.01, r = 0.86). Total MPA concentration increased during the 3 months, but not in patients on tacrolimus. High CsA C2 lowered the acute rejection rate and plasma MPA. High CsA C2 is associated with elevated GGT, probably because of cholestatic effects, which explain the increased MPAG-to-MPA ratio. Increasing MPA concentration is ascribed to per-protocol CsA C2 reductions. In conclusion, CsA may confound the relationship between MPA and the incidence of rejection, and contribute to the difficulty of obtaining a therapeutic range for MPA in clinical practice.

ROLE OF MRP2 IN THE HEPATIC DISPOSITION OF MYCOPHENOLIC ACID AND ITS GLUCURONIDE METABOLITES: EFFECT OF CYCLOSPORINE

Mycophenolic acid (MPA) is part of the immunosuppressant therapy for transplant recipients. This study examines the role of the canalicular transporter, Mrp2, and the effect of cyclosporin A (CsA), on the biliary secretion of the ether (MPAGe) and acyl (MPAGa) glucuronides of MPA. Isolated livers from Wistar rats (n = 6), or Wistar TR- rats (n = 6) were perfused with MPA (5 mg/l). A third group of Wistar rats (n = 6) was perfused with MPA and CsA (250 microg/l). There was no difference in the half-life, hepatic extraction ratio (E(H)), clearance or partial clearance of MPA to MPAGe, but there was a difference in partial clearance to MPAGa between control and CsA groups (0.9 +/- 0.4 versus 0.5 +/- 0.1 ml/min). TR- rats had a lower E(H) (0.59 +/- 0.30 versus 0.95 +/- 0.30), a lower clearance (18 +/- 8 versus 29 +/- 7 ml/min), and a longer half-life (19.5 +/- 10.3 versus 10.1 +/- 2.4 min) than controls. Compared to controls, MPAGe and MPAGa biliary excretion was reduced by 99% and 71.8%, respectively, in TR- rats, and 17.5% and 53.8%, respectively, in the MPA-CsA group. The biliary excretion of MPAGe is mediated by Mrp2, whereas that of MPAGa seems to depend on both Mrp2 and another unidentified canalicular transporter. Although CsA can inhibit Mrp2, our data suggest that it may also inhibit the hepatic glucuronidation of MPA in Wistar rats.

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.

Validation of a high-performance liquid chromatography method for the measurement of mycophenolic acid and its glucuronide metabolites in plasma

OBJECTIVES

The need for therapeutic drug monitoring of the immunosuppressant mycophenolic acid is becoming more evident. This paper describes a simple high-performance liquid chromatography procedure for the simultaneous quantitation of mycophenolic acid (MPA) and its glucuronide metabolites in plasma using protein precipitation followed by HPLC analysis with isocratic elution and UV detection.

DESIGN AND METHODS

The performance of this method is compared to the EMIT 2000 MPA immunoassay (Dade Behring Diagnostics Inc., Cupertino, California, USA).

RESULTS AND CONCLUSION

Intra-assay precision and accuracy of calibrators were determined for MPA at 0.5 and 20 mg/L, MPAGe at 5 and 200 mg/L, and MPAGa at 2.5 and 100 mg/L and showed coefficients of variation of less than 5.0% and biases of less than 14.0%. Inter-assay precision and accuracy of quality control samples were determined for MPA at 2 and 15 mg/L, MPAGe at 20 and 150 mg/L and showed CVs of less than 5.0% and biases of less than 14%. The lower limit of quantitation of the method was determined for MPA at 0.25 mg/L, MPAGe at 0.5 mg/L, and MPAGa at 0.25 mg/L and showed CVs of less than 19% and biases of less than 20%. This method, compared to the EMIT 2000 MPA immunoassay, showed a linear regression analysis relationship of EMIT = 0.973 HPLC + 0.55 (r(2) = 0.851), and was determined to be suitable for therapeutic drug monitoring and pharmacokinetic studies of MPA.

Population pharmacokinetics of mycophenolic acid during the first week after renal transplantation

OBJECTIVE

To investigate the population pharmacokinetics of mycophenolic acid (MPA) in adult kidney transplant recipients during the crucial first week after transplantation.

METHODS

Data were collected from 117 patients. MPA plasma concentrations were determined at t=0, 1, 2, 3 and 4 h after mycophenolate mofetil dosing on days 3, 5 and 7. Population analysis was performed using NONMEM. Covariates screened were sex, age, body weight, serum creatinine, creatinine clearance, serum albumin, days of therapy, diabetes mellitus, organ source (live or cadaveric) and co-therapy (tacrolimus or cyclosporine). Final model validity was evaluated using 200 boot strapped samples from the original data. Bias and precision were determined through comparison of observed and predicted concentrations.

RESULTS

Individual concentration-time profiles showed evidence of an absorption lag time and enterohepatic recirculation of MPA in some patients on some occasions. The best base model had bi-exponential elimination with a typical population (SE%) apparent clearance (CL/F) of 29 l/h (5%) and apparent volume of the central compartment of 65 l (7%). CL/F decreased significantly with increasing serum albumin (1.42 l/h reduction in total plasma CL/F with each 1 g/l increase in albumin) and was 27% greater in patients receiving cyclosporine than in those receiving tacrolimus. Evaluation of the final model showed close agreement between pairs of boot strapped and final model parameter estimates (all differences <7%). Predictions were non-biased (0.11 mg/l) but imprecise (2.8 mg/l).

CONCLUSION

Population pharmacokinetic parameters for MPA were determined. These can be used to achieve specific target MPA concentrations or areas under the concentration-time curve.

Mycophenolic acid pharmacokinetics and related outcomes early after renal transplant

AIMS

The pharmacokinetics of mycophenolic acid and its glucuronide are complex. This study investigated the pharmacokinetics, pharmacodynamics and protein binding of mycophenolic acid and its glucuronide metabolite, early post-transplant in renal allograft recipients.

METHODS

Forty-two de novo renal transplant recipients receiving mycophenolate mofetil and concomitant cyclosporin (n = 32) or tacrolimus (n = 10) participated in the study. Blood samples were taken on day 5 post-transplant for measurement of free and total concentrations of mycophenolic acid, mycophenolic acid glucuronide and relevant biochemistry. Associations between free fraction and biochemistry were investigated. Free and total 6-h area under the concentration-time curve (AUC0-6) of mycophenolic acid was assessed relative to clinical outcomes in the first month post-transplant.

RESULTS

Kinetic variability of free and total mycophenolic acid and its glucuronide was greater in patients on cyclosporin (12- to 18-fold variation) than on tacrolimus (four- to fivefold) cotherapy. Cyclosporin-treated patients also had significantly lower predose total mycophenolic acid concentrations than tacrolimus-treated patients (median 0.8 mg l(-1) and 1.6 mg l(-1), respectively, P = 0.002). Mycophenolic acid glucuronide predose concentration correlated positively with mycophenolic acid glucuronide AUC0-6 (r > 0.95). Mycophenolic acid free fraction varied 11-fold, from 1.6% to 18.3%, whilst the glucuronide free fraction varied threefold, from 17.4% to 54.1%. Urea and creatinine concentrations correlated positively (r > 0.46), whilst albumin correlated negatively (r = -0.54) with free fraction of mycophenolic acid. Similar relationships were found for the free fraction of mycophenolic acid glucuronide. Mycophenolic acid free fraction was on average 70% higher in patients with albumin concentrations below a specified albumin cut-off concentration of 31 g l(-1)[free fraction = 7 +/- 4% for lower albumin and 4 +/- 3% for higher albumin, respectively; P = 0.001; 95% confidence interval (CI) for the difference 1.9, 4.2]. Neither free nor total mycophenolic acid AUC0-6 was related to rejection (P > 0.07). Free AUC0-6 was significantly higher in those patients with thrombocytopenic, leukopenic and/or infectious outcomes than in those without (mean +/- SD 1.9 +/- 0.3 mg h(-1) l(-1) and 1.1 +/- 0.1 mg h(-1) l(-1), P = 0.0043; 95% CI for the difference 0.3, 1.4).

CONCLUSIONS

The marked variability in mycophenolic acid/glucuronide pharmacokinetics occurring early post-transplant during the current study was greater in cyclosporin (12-18-fold) than in tacrolimus (four- to fivefold) treated patients. Concomitant cyclosporin was associated with total mycophenolic acid concentrations approximately half that of tacrolimus. Patients with marked renal impairment had the highest free fractions reported to date. The exposure to unbound mycophenolic acid was significantly related to infections and haematological toxicity.

Predictive factors of acute rejection after early cyclosporine withdrawal in renal transplant recipients who receive mycophenolate mofetil: results from a prospective, randomized trial

The aim of this randomized, open-labeled trial was to compare the incidence of acute rejection after an early (3 mo posttransplantation) withdrawal of cyclosporine (CsA) or mycophenolate mofetil (MMF) in renal transplantation. Among 218 eligible recipients, 108 nonsensitized, rejection-free patients who were under a triple drug regimen (CsA-MMF-prednisone) and had received a first kidney from a deceased donor were enrolled. At 3 mo after graft, they were gradually withdrawn from CsA (MMF group, n = 54) or MMF (CsA group, n = 54). A graft biopsy and a pharmacokinetic study of CsA and mycophenolic acid were systematically performed before the randomization. At 1 yr, graft and patient survival rates were 100% in each group. Renal function was improved in the MMF group compared with the CsA group (Cockcroft calculated clearance 64.7 +/- 18.7 versus 56.5 +/- 18.0 ml/min; P = 0.023). However, the probability of acute rejection was higher in the MMF group (18.5 versus 5.6%; P = 0.045). The 10 patients who developed acute rejection after CsA withdrawal had a significantly higher incidence of borderline changes on the randomization biopsy than the 44 rejection-free patients (five of 10 versus eight of 44; P = 0.034), and they displayed a lower area under the curve of mycophenolic acid (43 +/- 9 versus 58 +/- 22 mg/h per L; P = 0.045). Multivariate analysis confirmed that borderline changes and area under the curve of mycophenolic acid were significant risk factors of acute rejection after CsA discontinuation. It is concluded that a systematic graft biopsy and a pharmacokinetic study of mycophenolic acid are needed to reduce the risk for acute rejection after CsA withdrawal.