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

Analysis of risk factors and prognosis of diarrhea after renal transplantation

BACKGROUND

Diarrhea is a prevalent complication after renal transplantation.

OBJECTIVE

To examine the risk factors for diarrhea after renal transplantation, evaluate their combined predictive values, and analyze the prognosis.

METHODS

Clinical data of patients who underwent allogeneic renal transplantation in the Second People's Hospital of Shanxi Province from January 2019 to March 2020 were retrospectively analyzed, cases were screened and grouped, independent risk factors for diarrhea after renal transplantation were analyzed by univariate analysis and multivariate analysis, and their predictive value was evaluated by receiver operating characteristic (ROC) curve. The survival time of recipient grafts in diarrhea and non-diarrhea groups were evaluated by Kaplan-Meier and log-rank test.

RESULTS

We included 166 recipients in the study and the incidence of diarrhea was 25.9%; univariate and logistic regression multivariate analyses revealed that independent risk factors for diarrhea in recipients were that the type of renal transplant donor was DCD (donation after circulatory death), immunity induction was onducted with basiliximab + antithymocyte globulin (ATG), and ATG alone, the type of mycophenolic acid (MPA) used was mycophenolate mofetil capsules, and delayed graft function (DGF) occurred after transplantation. The ROC curve indicated that the combination of the four factors had good accuracy in predicting the occurrence of diarrhea in recipients. The graft survival rate two years after the operation in the diarrhea group was significantly lower than that in the non-diarrhea group.

CONCLUSION

Diarrhea affected the two-year survival rate of the graft. The type of donor, immunity induction scheme, and the type of MPA and DGF were independent risk factors for diarrhea in recipients, and the combination of the four factors had good prognostic prediction value.

Noninvasive testing for mycophenolate exposure in children with renal transplant using urinary metabolomics

BACKGROUND

Despite the common use of mycophenolate in pediatric renal transplantation, lack of effective therapeuic drug monitoring increases uncertainty over optimal drug exposure and risk for adverse reactions. This study aims to develop a novel urine test to estimate MPA exposure based using metabolomics.

METHODS

Urine samples obtained on the same day of MPA pharmacokinetic testing from two prospective cohorts of pediatric kidney transplant recipients were assayed for 133 unique metabolites by mass spectrometry. Partial least squares (PLS) discriminate analysis was used to develop a top 10 urinary metabolite classifier that estimates MPA exposure. An independent cohort was used to test pharmacodynamic validity for allograft inflammation (urinary CXCL10 levels) and eGFR ratio (12mo/1mo eGFR) at 1 year.

RESULTS

Fifty-two urine samples from separate children (36.5% female, 12.0 ± 5.3 years at transplant) were evaluated at 1.6 ± 2.5 years post-transplant. Using all detected metabolites (n = 90), the classifier exhibited strong association with MPA AUC by principal component regression (r = 0.56, p < .001) and PLS (r = 0.75, p < .001). A practical classifier (top 10 metabolites; r = 0.64, p < .001) retained similar accuracy after cross-validation (LOOCV; r = 0.52, p < .001). When applied to an independent cohort (n = 97 patients, 1053 samples), estimated mean MPA exposure over Year 1 was inversely associated with mean urinary CXCL10:Cr (r = -0.28, 95% CI -0.45, -0.08) and exhibited a trend for association with eGFR ratio (r = 0.35, p = .07), over the same time period.

CONCLUSIONS

This urinary metabolite classifier can estimate MPA exposure and correlates with allograft inflammation. Future studies with larger samples are required to validate and evaluate its clinical application.

Genetic Polymorphisms Affecting Tacrolimus Metabolism and the Relationship to Post-Transplant Outcomes in Kidney Transplant Recipients

Background

Tacrolimus is a key drug in kidney transplantation with a narrow therapeutic index. However, whether tacrolimus exposure variability affects clinical outcomes and adverse reactions remains unknown.

Objective

Our study investigated the factors that influence tacrolimus exposure in kidney transplantation recipients and the relationship between tacrolimus concentration and clinical outcomes and adverse reactions.

Settings and Methods

We examined the effect of tacrolimus concentration on clinical outcomes and adverse reactions in 201 kidney transplantation recipients, and identified clinical and pharmacogenetic factors that explain tacrolimus exposure.

Results

The CYP3A5 genotype was clearly associated with dose-adjusted trough blood tacrolimus concentrations (C₀/D), whereas no significant difference was observed in patients with the CYP3A4*1B, CYP3A4*22, ABCB1, ABCC2, POR*28 or PXR alleles. Clinical factors such as red blood cell count, hemoglobin, and albumin were the most useful influence factors affecting tacrolimus C₀/D. Besides, Wuzhi capsule increased tacrolimus C₀/D in kidney transplantation recipients. Furthermore, higher tacrolimus concentrations were associated with higher diarrhea and post-transplant diabetes mellitus (PTDM) risk but not with acute rejection and chronic allograft kidney dysfunction.

Conclusion

Clinical factors, medication, and CYP-enzyme polymorphisms accounted for tacrolimus concentration variability in kidney transplantation recipients. Furthermore, higher tacrolimus concentrations were associated with higher diarrhea and PTDM risk.

Discrepancy between self-perceived mycophenolic acid-associated diarrhea and stool water content after kidney transplantation

BACKGROUND

Diarrhea is a well-known side effect of mycophenolic acid (MPA) use in kidney transplant recipients (KTRs). It is unknown whether self-reported diarrhea using the Modified Transplant Symptom Occurrence and Symptom Distress Scale (MTSOSD-59R) corresponds to stool water content and how both relate to MPA usage.

METHODS

MTSOSD-59R questionnaires filled out by 700 KTRs from the TransplantLines Biobank and Cohort Study (NCT03272841) were analyzed and compared with stool water content. Stool samples (N = 345) were freeze-dried, and a water content ≥80% was considered diarrhea.

RESULTS

Self-perceived diarrhea was reported by 46%, while stool water content ≥80% was present in 23% of KTRs. MPA use was not associated with self-perceived diarrhea (odds ratio(OR) 1.32; 95% confidence interval(CI), 0.87-1.99, p = .2), while it was associated with stool water content ≥80% (OR 2.88; 95%CI, 1.41-5.89, p = .004), independent of potential confounders. Adjustment for prior MPA discontinuation because of severe diarrhea, uncovered an association between MPA use and self-perceived diarrhea (OR 1.80; 95%CI, 1.13-2.89, p = .01).

CONCLUSIONS

These results suggest that reporting bias could add to the discrepancy between both methods for diarrhea assessment. We recommend use of objective biomarkers or more extensive questionnaires which assess information on stool frequency and stool consistency, to investigate post-transplantation diarrhea.

Diarrhea in the pediatric solid organ transplantation recipient: A multidisciplinary approach to diagnosis and management

Diarrhea in the pediatric solid organ transplantation (SOT) recipient is a frequent complaint that is associated with significant morbidity and impaired quality of life. There are limited published data regarding the specific epidemiology, diagnostic evaluation, and treatment of diarrhea after SOT in children. Pediatric SOT recipients have an increased risk of developing diarrhea because of a generalized immunosuppressed state, epidemiologic exposures, and polypharmacy. There is a need to standardize the diagnostic evaluation of diarrhea in children after SOT to facilitate an accurate diagnosis and timely treatment. Herein, we review the available published data and propose a systematic, stepwise approach to the evaluation of diarrhea in this high-risk population, focusing on timely diagnosis of both infectious and non-infectious causes, in order to provide focused management. Prospective studies are needed to better assess the true prevalence, risk factors for, etiologies, and complications of diarrhea in pediatric SOT patients that will guide optimal management. Development of effective vaccines and antiviral therapies for enteric viruses may also contribute to improved outcomes.

Antitumor pharmacotherapy of colorectal cancer in kidney transplant recipients

Renal transplantation has become the sole most preferred therapy modality for end-stage renal disease patients. The growing tendency for renal transplants, and prolonged survival of renal recipients, have resulted in a certain number of post-transplant colorectal cancer patients. Antitumor pharmacotherapy in these patients is a dilemma. Substantial impediments such as carcinogenesis of immunosuppressive drugs (ISDs), drug interaction between ISDs and anticancer drugs, and toxicity of anticancer drugs exist. However, experience of antitumor pharmacotherapy in these patients is limited, and the potential risks and benefits have not been reviewed systematically. This review evaluates the potential impediments, summarizes current experience, and provides potential antitumor strategies, including adjuvant, palliative, and subsequent regimens. Moreover, special pharmaceutical care, such as ISDs therapeutic drug monitoring, metabolic enzymes genotype, and drug interaction, are also highlighted.

Determination of mycophenolic acid in human plasma by ultra-performance liquid chromatography-tandem mass spectrometry and its pharmacokinetic application in kidney transplant patients

To implement and validate an analytical method by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC MS/MS) to quantify mycophenolic acid (MPA) in kidney transplant patients. Quantification of MPA was performed in an ACQUITY UPLC H Class system coupled to a Xevo TQD detector and it was extracted from plasma samples by protein precipitation. The chromatographic separation was achieved through an ACQUITY HSS C₁₈ SB column with 0.1% formic acid and acetonitrile (60:40 vol/vol) as mobile phase. The pharmacokinetic parameters were calculated by non-compartmental analysis of MPA plasma concentrations from 10 kidney transplant patients. The linear range for MPA quantification was 0.2-30 mg/L with a limit of detection of 0.07 mg/L; the mean extraction recovery was 99.99%. The mean intra- and inter-day variability were 2.98% and 3.4% with a percentage of deviation of 8.4% and 6.6%, respectively. Mean maximal concentration of 10 mg/L at 1.5 h, area under the concentration-time curve of 36.8 mg·h/L, elimination half-life of 3.9 h, clearance of 0.32 L/h/kg and volume of distribution of 1.65 L/kg were obtained from MPA pharmacokinetics profiles. A simple, fast and reliable UPLC-MS/MS method to quantify MPA in plasma was validated and has been applied for pharmacokinetic analysis in kidney transplant patients.

Influence of Calcineurin Inhibitor and Sex on Mycophenolic Acid Pharmacokinetics and Adverse Effects Post-Renal Transplant

Tacrolimus or cyclosporine is prescribed with mycophenolic acid posttransplant and contributes to interpatient variability in mycophenolic acid pharmacokinetics and response. Cyclosporine inhibits enterohepatic circulation of the metabolite mycophenolic acid glucuronide, which is not described with tacrolimus. This study investigated mycophenolic acid pharmacokinetics and adverse effects in stable renal transplant recipients and the association with calcineurin inhibitors, sex, and race. Mycophenolic acid and mycophenolic acid glucuronide area under the concentration-time curve from 0 to 12 hours (AUC_0-12h ) and apparent clearance were determined at steady state in 80 patients receiving cyclosporine with mycophenolate mofetil and 67 patients receiving tacrolimus with mycophenolate sodium. Gastrointestinal adverse effects and hematologic parameters were evaluated. Statistical models evaluated mycophenolic acid pharmacokinetics and adverse effects. Mycophenolic acid AUC_0-12h was 1.70-fold greater with tacrolimus (68.9 ± 30.9 mg·h/L) relative to cyclosporine (40.8 ± 17.6 mg·h/L); P < .001. Target mycophenolic acid AUC_0-12h of 30-60 mg·h/L was achieved in 56.3% on cyclosporine compared with 34.3% receiving tacrolimus (P < .001). Mycophenolic acid clearance was 48% slower with tacrolimus (10.6 ± 4.7 L/h) relative to cyclosporine (20.5 ± 10.0 L/h); P < .001. Enterohepatic circulation occurred less frequently with cyclosporine (45%) compared with tacrolimus (78%); P < 0.001; with a 2.9-fold greater mycophenolic acid glucuronide AUC_0-12h to mycophenolic acid AUC_0-12h ratio (P < .001). Race did not affect mycophenolic acid pharmacokinetics. Gastrointestinal adverse effect scores were 2.2-fold higher with tacrolimus (P < .001) and more prominent in women (P = .017). Lymphopenia was more prevalent with tacrolimus (52.2%) than cyclosporine (22.5%); P < 0.001. Calcineurin inhibitors and sex contributed to interpatient variability in mycophenolic acid pharmacokinetics and adverse effects post-renal transplant, which could be attributed to differences in enterohepatic circulation.

Immunosuppressive drugs and the gastrointestinal tract in renal transplant patients

Gastrointestinal (GI) discomfort is common after renal transplantation and can be caused by the use of various immunosuppressive drugs. GI symptoms affect the quality of life, lead to an impaired graft survival and an increased mortality. Moreover, diseases and disturbances of the GI tract also affect the pharmacokinetics of immunosuppressive drugs. This review addresses the interaction between immunosuppressive agents and GI disorders. The GI tract is involved in the metabolism of several immunosuppressive drugs. Calcineurin inhibitors, mTor inhibitors, and corticosteroids are subjected to metabolism by the intestinal cytochrome P450 (CYP3A) and by the drug efflux pump ABCB1. Mycophenolate is partly metabolized in the stomach and intestine and undergoes enterohepatic recirculation. Gastrointestinal disturbances can lead to a modified exposure to immunosuppressive drugs. In the first and second part of this review, we focus on the role of the GI tract in the pharmacokinetics of the immunosuppressive drugs and how to adjust immunosuppressive therapy in patients with vomiting, need for tube feeding, delayed gastric emptying, intestinal resection, and diarrhea. In the third part, we review the GI adverse effects of the various immunosuppressive drugs, with special attention for diarrhea and dyspepsia. Finally, we discuss the effects of drugs used for relief of GI complaints on the exposure to immunosuppressive agents.

Adverse Events under Tacrolimus and Cyclosporine in the First 3 Years Post-Renal Transplantation in Children

BACKGROUND

Progress in immunosuppression has reduced acute rejection, graft loss and mortality after renal transplantation. Adverse drug reactions are well described in adults but few data are available in children. Our objectives were to analyse the adverse events reported in the first 3 years post-transplantation in children receiving tacrolimus or cyclosporine-based immunosuppression and compare them with the information of the Summary of Product Characteristics.

METHODS

This retrospective study included all children who underwent a renal transplant at Hospital Robert Debré between 2002 and 2015. Initial immunosuppression was based on induction, calcineurin inhibitor, mycophenolate mofetil and corticosteroids. Adverse events were collected from medical records and coded using the Medical Dictionary for Regulatory Activities and the implications of tacrolimus and cyclosporine analysed. Statistical analyses were performed using SAS 9.4.

RESULTS

One hundred and twenty-five children were included. During the observation period [2.7 years (0.6-4.3)], 105 patients received tacrolimus and 39 received cyclosporine. The incidence rate for gastrointestinal disorders was 0.128 and 0.056 by patient-years of exposure (p < 0.05), under tacrolimus and cyclosporine schedules. For neutropenia, it was 0.064 and 0.014 (p < 0.05). The frequencies of toxic nephropathy and gastrointestinal pain were higher than those in the Summary of Product Characteristics of tacrolimus (> 20%) and cyclosporine (> 10%). Cosmetic events for cyclosporine and neutropenia for tacrolimus were frequently observed (18 and 14.3%, respectively), although uncommon in the Summary of Product Characteristics.

CONCLUSIONS

The exposure-adjusted incidence rate of gastrointestinal disorders and neutropenia was higher in children under the tacrolimus schedule. Our findings contribute to the evaluation of the benefit-risk balance of immunosuppressive therapy following paediatric renal transplantation.

Intestinal infection at onset of mycophenolic acid-associated chronic diarrhea in kidney transplant recipients

BACKGROUND

Chronic diarrhea after kidney transplantation is often attributed to mycophenolic acid (MPA) toxicity. We hypothesize that intestinal infections contribute to the pathogenesis of chronic MPA-associated diarrhea.

METHODS

In this retrospective study, all patients (n = 726) receiving a kidney transplant between 2000 and 2010 at the University Hospital Zurich were followed until July 2014 for occurrence of chronic diarrhea (≥4 weeks). Infectious triggers at diarrhea onset were assessed by reviewing medical history, stool microbiology, and histology of colon biopsies.

RESULTS

In 46 patients (6.3% of the cohort), a total of 51 episodes of chronic diarrhea during MPA treatment were documented. The diarrhea episodes were often severe, as confirmed by significant weight loss. The cumulative incidence of chronic diarrhea was uniformly distributed throughout the post-transplant period, with 2.0%, 5.1%, and 9.6% at 1, 5, and 10 years, respectively. Evidence was found for intestinal infection at diarrhea onset in 38 episodes (74.5%). Occurrence of diarrhea onset showed a seasonal distribution with peaks in April and October/November. Specific antimicrobial treatment alone was associated with a 19% resolution rate only, whereas combination with dose reduction of MPA or switch from mycophenolate mofetil to enteric-coated mycophenolate sodium resulted in a 22.7% and 76.5% resolution rate, respectively. Change to an MPA-free regimen was associated with a 100% resolution rate.

CONCLUSION

These results provide first evidence for a contribution of intestinal infections in chronic post-transplant diarrhea associated with MPA treatment.

Simple and Sensitive High-Performance Liquid Chromatography (HPLC) Method with UV Detection for Mycophenolic Acid Assay in Human Plasma. Application to a Bioequivalence Study

PURPOSE

A simple and available reversed-phase high performance liquid chromatography (HPLC) method with UV detection has been developed and validated for mycophenolic acid (MPA) assay in human plasma.

METHODS

MPA was extracted from plasma with protein precipitation method by acetonitrile: percholeric acid: methanol (75:5:20 v/v/v). The drug separation was achieved using a C8 analytical column and a mobile phase of 0.1M triethylammonium phosphate (pH=5.4)-acetonitril (65:35, v/v), with a flow rate of 1.5 ml/min. The detection wavelength was 304 nm. Limit of detection (LOD) of the method was determined as the lowest MPA concentration producing a signal-to-noise (S/N) ratio of about 3. Limit of quantitation (LOQ) was determined as the lowest MPA concentration capable of being quantitated with enough accuracy and precision.

RESULTS

The method showed significant linear response-concentration relationship throughout the MPA concentration range of 0.2-10 µg/ml. A typical linear regression equation of the method was: y = 8.5523 x + 0.094, with x and y representing MPA concentration (in µg/ml) and peak height respectively, and the regression coefficient (r) of 0.9816. The average within-run and between-run variations of 7.81 and 4.78 percent. The average drug recovery from plasma was 95.24 percent throughout the linear concentration range. The limits of detection (LOD) and quantitation (LOQ) of the method were 0.05 and 0.2 µg/ml, respectively. The practical applicability of the method was proven throughout a bioequivalence study.

CONCLUSION

The results showed the acceptable degree of linearity, sensitivity, precision, accuracy and recovery for the method. The method was used successfully for quantitation of MPA in plasma samples of healthy volunteers throughout a bioequivalence study.

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).

Unusually late-onset mycophenolate mofetil-related colitis

PURPOSE

Serious gastrointestinal complications arising 13 years after the initiation of posttransplant immunosuppressant therapy with mycophenolate mofetil are reported.

SUMMARY

Over a three-month period, a male heart transplant recipient who had taken oral mycophenolate mofetil (2 g daily) for 13 years as part of an immunosuppressant maintenance regimen developed diarrhea and weight loss leading to renal failure and metabolic acidosis. There was no evidence of opportunistic infection, and immunostaining for cytomegalovirus yielded negative results. Colonoscopy revealed areas of congested, erythematous, and nodular mucosa. Histological examination of mucosal biopsy specimens revealed pathological abnormalities typical of those seen in cases of mycophenolate mofetil-associated colitis. On discontinuation of mycophenolate mofetil use, the patient's diarrhea resolved and his renal function improved. Colitis, diarrhea, and other gastrointestinal complications are commonly reported in patients receiving mycophenolate mofetil, an immunosuppressant widely used to prevent rejection of solid organ or bone marrow transplants; however, the onset of such symptoms after more than a decade of continuous use of the drug has not been previously reported. This case suggests that mycophenolate mofetil toxicity should be considered in the evaluation of late-onset posttransplant diarrhea regardless of the duration of therapy.

CONCLUSION

A 33-year-old man maintained on mycophenolate mofetil for 13 years after heart transplantation developed diarrhea, weight loss, and acute kidney injury over a three-month period. Colonoscopy and biopsy revealed pathological changes consistent with mycophenolate mofetil toxicity, and the patient's symptoms resolved after the drug was discontinued.

Pharmacology and toxicology of mycophenolate in organ transplant recipients: an update

This review aims to provide an update of the literature on the pharmacology and toxicology of mycophenolate in solid organ transplant recipients. Mycophenolate is now the antimetabolite of choice in immunosuppressant regimens in transplant recipients. The active drug moiety mycophenolic acid (MPA) is available as an ester pro-drug and an enteric-coated sodium salt. MPA is a competitive, selective and reversible inhibitor of inosine-5'-monophosphate dehydrogenase (IMPDH), an important rate-limiting enzyme in purine synthesis. MPA suppresses T and B lymphocyte proliferation; it also decreases expression of glycoproteins and adhesion molecules responsible for recruiting monocytes and lymphocytes to sites of inflammation and graft rejection; and may destroy activated lymphocytes by induction of a necrotic signal. Improved long-term allograft survival has been demonstrated for MPA and may be due to inhibition of monocyte chemoattractant protein 1 or fibroblast proliferation. Recent research also suggested a differential effect of mycophenolate on the regulatory T cell/helper T cell balance which could potentially encourage immune tolerance. Lower exposure to calcineurin inhibitors (renal sparing) appears to be possible with concomitant use of MPA in renal transplant recipients without undue risk of rejection. MPA displays large between- and within-subject pharmacokinetic variability. At least three studies have now reported that MPA exhibits nonlinear pharmacokinetics, with bioavailability decreasing significantly with increasing doses, perhaps due to saturable absorption processes or saturable enterohepatic recirculation. The role of therapeutic drug monitoring (TDM) is still controversial and the ability of routine MPA TDM to improve long-term graft survival and patient outcomes is largely unknown. MPA monitoring may be more important in high-immunological recipients, those on calcineurin-inhibitor-sparing regimens and in whom unexpected rejection or infections have occurred. The majority of pharmacodynamic data on MPA has been obtained in patients receiving MMF therapy in the first year after kidney transplantation. Low MPA area under the concentration time from 0 to 12 h post-dose (AUC0-12) is associated with increased incidence of biopsy-proven acute rejection although AUC0-12 optimal cut-off values vary across study populations. IMPDH monitoring to identify individuals at increased risk of rejection shows some promise but is still in the experimental stage. A relationship between MPA exposure and adverse events was identified in some but not all studies. Genetic variants within genes involved in MPA metabolism (UGT1A9, UGT1A8, UGT2B7), cellular transportation (SLCOB1, SLCO1B3, ABCC2) and targets (IMPDH) have been reported to effect MPA pharmacokinetics and/or response in some studies; however, larger studies across different ethnic groups that take into account genetic linkage and drug interactions that can alter a patient's phenotype are needed before any clinical recommendations based on patient genotype can be formulated. There is little data on the pharmacology and toxicology of MPA in older and paediatric transplant recipients.

Mycophenolic acid-related diarrhea is not associated with polymorphisms in SLCO1B nor with ABCB1 in renal transplant recipients

OBJECTIVE

We investigated the association between genetic polymorphisms in ABCB1 and SLCO1B and mycophenolic acid (MPA) pharmacokinetics, and MPA-related diarrhea and leukopenia in 338 kidney transplant recipients.

METHODS

A total of 338 patients participating in an international, randomized-controlled clinical trial were genotyped for ABCB1 and SLCO1B. Patients were all treated with mycophenolate mofetil and either cyclosporine or tacrolimus. MPA-area under the curve (AUCs), MPA-glucuronide AUCs and acylglucuronide-AUCs were measured on days 3 and 10, and months 1, 3, 6, and 12 after kidney transplantation.

RESULTS

The risk of developing diarrhea was 1.8-fold higher in patients cotreated with tacrolimus compared with patients cotreated with cyclosporine (95% confidence interval: 1.03-3.13; P=0.038). ABCB1 and SLCO1B SNPs were not associated with dose-adjusted exposure to MPA, MPA-glucuronide, nor acylglucuronide-MPA nor with the incidence of diarrhea or leukopenia.

CONCLUSION

Genotyping for ABCB1 or SLCO1B pretransplantation is unlikely to be of clinical value for individualization of MPA therapy.

Next level of immunosuppression: drug/immune monitoring

1. Current immunological monitoring relies heavily on clinical judgment and therapeutic drug levels and does not adequately assess the functional or donor-specific immunosuppression (IS) status of recipients of liver transplantation (LT). 2. Trough levels of drugs are arbitrary and are more clinically relevant for preventing supratherapeutic or subtherapeutic dosing and blood concentrations and for more closely monitoring at-risk populations (children, the elderly, and patients with organ dysfunction). The AUC or the post-dose levels may be more precise, but they have not been used extensively by transplant centers. 3. Data on drug/immune monitoring specific to LT are fairly limited; therefore, clinical practice is often borrowed from experiences with nonhepatic transplantation (mainly renal transplantation). 4. The monitoring of drug levels in patients taking generic immunosuppressants is challenging because the formulations may change with each prescription. The monitoring of drug or antibody levels is not yet clinically available for biological therapies (induction, lymphocyte-depleting, and maintenance agents). 5. Polymorphisms in drug metabolism (cytochrome P450 and P-glycoprotein) may be useful in selecting the initial and maintenance dosages of immunosuppressants and in preventing complications from over or underimmunosuppression. 6. Future immune monitoring assays should be focused on genomic or immunological predispositions and on specific reactivities to donor antigens to guide the appropriate dosing and minimization of IS after LT.

ATP-binding cassette transporters as pharmacogenetic biomarkers for kidney transplantation

Immunosuppressive drugs used in organ transplantation are highly effective in preventing acute rejection. However, the clinical use of these drugs is complicated by the fact that they display highly variable pharmacokinetics and pharmacodynamics between individual patients. The influence of genetic variation on the interindividual variability in immunosuppressive drug disposition, efficacy, and toxicity has been explored in recent years. The polymorphically-expressed ATP-binding cassette (ABC) transporter proteins, in particular ABCB1 and ABCC2, have been investigated extensively because they play an important role in the absorption, distribution and elimination of many immunosuppressive drugs in use today. From these studies it can be concluded that polymorphisms in ABCB1 and ABCC2 have no consistent effect on immunosuppressant pharmacokinetics and toxicity although polymorphisms in ABCB1 appear to be related to the risk of developing calcineurin inhibitor-related nephrotoxicity. However, the latter needs to be replicated before an individual's ABCB1 genotype can become a useful marker that is applied in clinical practice. Future studies evaluating the influence of ABC transporter gene polymorphisms should explore the relationship with intracellular rather than systemic drug concentrations further in well-designed clinical studies. Until then, single-nucleotide polymorphisms in ABC transporter genes are not suitable to act as biomarkers for solid organ transplantation.

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.

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.

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.

SLCO1B1 genetic polymorphism influences mycophenolic acid tolerance in renal transplant recipients

AIMS

This study aimed to determine the influence of gene candidates on mycophenolic acid (MPA) response during the first year of renal transplantation.

MATERIALS & METHODS

A total of 218 renal transplant recipients who received MPA from the first day of transplantation at a fixed dose of 2 g/day were genotyped for ABCB1, ABCC2, UGT2B7, UGT1A9, SLCO1B1, SLCO1B3 and IMPDH1 polymorphisms. Clinical end points were MPA-related adverse drug reactions (ADRs) and acute rejection episodes during the first year post-transplantation.

RESULTS

After correction for multiple statistical testing, SLCO1B1 (encoding the hepatic uptake transporter OATP1B1) was the only gene associated with MPA-related ADRs, showing a 75% risk reduction in favor of a protective effect of the SLCO1B1*5 allele (p = 0.002). In vitro experiments showed that MPA metabolites MPA-phenyl-glucuronide and MPA-acyl-glucuronide are substrates of OATP1B1. Their transport was decreased in the presence of the variant transporter (OATP1B1*5).

CONCLUSION

These results suggest for the first time that carriers of the SLCO1B1*5 allele seem to be protected from MPA-related ADRs.

Risk of diarrhoea in a long-term cohort of renal transplant patients given mycophenolate mofetil: the significant role of the UGT1A8 2 variant allele

AIM

In renal transplant patients given mycophenolate mofetil (MMF), we investigated the relationship between the digestive adverse events and polymorphisms in the UGT genes involved in mycophenolic acid (MPA) intestinal metabolism and biliary excretion of its phase II metabolites.

METHODS

Clinical data and DNA from 256 patients transplanted between 1996 and 2006 and given MMF with cyclosporin (CsA, n = 185), tacrolimus (TAC, n = 49) or sirolimus (SIR, n = 22), were retrospectively analysed. The relationships between diarrhoea and polymorphisms in UGT1A8 (2; 518C>G, 3; 830G>A), UGT1A7 (622C>T), UGT1A9 (-275T>A), UGT2B7 (-840G>A) and ABCC2 (-24C>T, 3972C>T) or the co-administered immunosuppressant were investigated using the Cox proportional hazard model.

RESULTS

Multivariate analysis showed that patients on TAC or SIR had a 2.8 higher risk of diarrhoea than patients on CsA (HR = 2.809; 95%CI (1.730, 4.545); P < 0.0001) and that non-carriers of the UGT1A8 2 allele (CC518 genotype) had a higher risk of diarrhoea than carriers (C518G and 518GG genotypes) (HR = 1.876; 95%CI (1.109, 3.175); P = 0.0192). When patients were divided according to the immunosuppressive co-treatment, a significant effect of UGT1A8 2 was found in those co-treated with CsA (HR = 2.414; 95%CI (1.089, 5.354); P = 0.0301) but not TAC or SIR (P = 0.4331).

CONCLUSION

These results suggest that a possible inhibition of biliary excretion of MPA metabolites by CsA and a decreased intestinal production of these metabolites in UGT1A8 2 carriers may be protective factors against MMF-induced diarrhoea.

The occurrence of diarrhea not related to the pharmacokinetics of MPA and its metabolites in liver transplant patients

PURPOSE

Mycophenolate mofetil (MMF) is a pro-drug that is hydrolyzed to release mycophenolic acid (MPA). Subsequently MPA is extensively metabolized to phenyl mycophenolic acid glucuronide (MPAG) and MPA acyl glucuronide (AcMPAG). It was presumed that the closest association is between plasma AcMPAG concentrations and the incidence of diarrhea. This study aimed to investigate the correlation between pharmacokinetics of MPA, MPAG, and AcMPAG and diarrhea in liver transplant recipients on MMF with tacrolimus.

METHODS

Sixty-seven patients receiving liver transplantation were included. The pharmacokinetics of MPA and its metabolites were monitored repeatedly in the early stage (within 2 weeks) and in the late stage after transplant. The plasma concentrations of MPA, MPAG, and AcMPAG were determined by the HPLC method.

RESULTS

Twenty-two patients (32.8%) suffered from episodes of diarrhea. Compared with the data from the early stage, AUC(0-12h) of MPA, MPAG, and AcMPAG increased significantly in both groups in the later stage. AUC(0-12h) of MPA, MPAG, and AcMPAG were not different significantly between the group with diarrhea and the group without diarrhea, either in the early stage or in the late stage (P > 0.05).

CONCLUSION

These results suggest that systemic exposures to MPA and its metabolites are not associated with the incidence of diarrhea in liver transplant recipients.

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

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

Genetic polymorphisms of MRP2 and UGT2B7 and gastrointestinal symptoms in renal transplant recipients taking mycophenolic acid

The aim of this study was to determine the relationship between single nucleotide polymorphisms in multidrug resistance protein 2 (MRP2) and uridine diphosphate glucuronosyltransferase (UGT) 2B7 and the severity of gastrointestinal (GI) symptoms in patients receiving mycophenolic acid (MPA). A total of 67 renal transplant recipients taking MPA derivatives were included in the study. Genotypes for MRP2 C-24 T and UGT2B7 C802 T were determined. The incidence and severity of GI symptoms were assessed using the validated Gastrointestinal Symptom Rating Scale (GSRS) at baseline, 2 weeks, 3 months, and 6 months after transplantation. The mean overall GSRS score and the score on the subscale for diarrhea were compared using the Kruskal-Wallis test. The overall GSRS scores (23.5 +/- 4.5 vs. 26.7 +/- 9.9, P = 0.68) or diarrhea subscores (3.5 +/- 0.9 vs. 5.1 +/- 3.3, P = 0.08) were not significantly different among patients with the heterozygous variant MRP2 C-24 T and those with the homozygous wild type. For UGT2B7, the overall mean GSRS scores were significantly different between the homozygous wild type and the variant type (CC vs. CT + TT, 29.2 +/- 9.3 vs. 24.0 +/- 8.2, P = 0.009), although diarrhea subscale scores did not reach statistical significance (CC vs. CT + TT, 5.7 +/- 4.1 vs. 4.1 +/- 1.9, P = 0.13). When the genotypes for MRP2 and UGT2B7 were considered together, patients with the variant forms of MRP2 and UGT2B7 had significantly lower overall GSRS scores (CC-CC vs. CT-CT/TT, 22.5 +/- 4.3 vs. 30.1 +/- 10.1, P = 0.04) and diarrhea subscale scores compared to wild type (CC-CC vs. CT-CT/TT, 3.4 +/- 0.7 vs. 6.2 +/- 4.4, P = 0.03). However, there were no differences in GSRS scores between patients receiving either mycophenolic mofetil (MMF) or enteric-coated mycophenolic acid (EC-MPA) regardless of whether the patients were receiving different calcineurin inhibitors. In conclusion, this study suggests that among patients receiving MPA, those with UGT2B7 variant genotypes are protected from the GI side effects of MPA regardless of the formulation used or concurrent calcineurin inhibitors administered. MRP2 genotypes did not show significant differences in GI side effects among patients taking MPA therapy.

The acyl glucuronide metabolite of mycophenolic acid induces tubulin polymerization in vitro

OBJECTIVES

The acyl glucuronide (AcMPAG) of mycophenolic acid (MPA) forms covalent protein adducts and possesses antiproliferative properties independent of IMPDH inhibition. The underlying mechanism is unknown. Disorganized tubulin polymerization prevents cell cycle progression. We investigated whether AcMPAG interacts with tubulin polymerization.

DESIGN AND METHODS

AcMPAG (1.0-100 microM) was incubated with bovine tubulin in the presence of GTP. Polymerization was followed at 340 nm. The time until onset and the extent of polymerization were determined. MPA (100 microM), phenolic glucuronide MPAG (100 microM), and paclitaxel (10 microM) served as controls.

RESULTS

MPAG was without effect. The AcMPAG effect on tubulin polymerization was dose dependent and significantly stronger (about 2.5-fold) than that of MPA (n=4; p<0.05), but weaker than paclitaxel.

CONCLUSIONS

MPA and AcMPAG can induce tubulin polymerization in the presence of GTP with AcMPAG being significantly stronger. This property of AcMPAG may contribute to its IMPDH independent antiproliferative effect.

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.

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.

The pharmacokinetics of mycophenolate mofetil in renal transplant recipients receiving standard-dose or low-dose cyclosporine, low-dose tacrolimus or low-dose sirolimus: the Symphony pharmacokinetic substudy

BACKGROUND

Exposure to mycophenolic acid (MPA), the primary active metabolite of mycophenolate mofetil (MMF), is correlated with therapeutic efficacy of MMF but varies depending on the concomitantly administered immunosuppressive drugs.

METHODS

A 3-month pharmacokinetic substudy of the prospective, randomized, multicentre, open-label Symphony study was performed. Eighty-three adult renal transplant patients received standard-dose cyclosporine, MMF 2 g/day and corticosteroids, or daclizumab induction, MMF 2 g/day and corticosteroids plus low-dose cyclosporine, low-dose tacrolimus or low-dose sirolimus. The area under the concentration-time curve (AUC(0-12)) of MPA and its metabolites between treatment groups was compared. Pharmacokinetic sampling was performed before MMF administration and at 20, 40, 75 min; 2, 3, 6, 8, 10 and 12 h post-dose on Day 7 and Months 1 and 3.

RESULTS

Compared with standard-dose cyclosporine, patients receiving low-dose tacrolimus or low-dose sirolimus had significantly higher AUC(0-12) values for MPA at Day 7 and Month 1 and for free MPA at Day 7, and significantly lower AUC(0-12) values for 7-O-MPA-glucuronide (MPAG) at Month 1 and for acyl-glucuronide at Months 1 and 3 (P < 0.05). AUC(0-12) of MPA and free MPA was significantly greater with low-dose tacrolimus and low-dose sirolimus than with low-dose cyclosporine in the first month (P < 0.05). The ratio of MPA to MPAG exposure was significantly higher in the three low-dose groups than in the standard-dose cyclosporine group (P < 0.05).

CONCLUSIONS

Standard- and low-dose cyclosporine reduces the exposure of MPA and free MPA compared to low-dose tacrolimus or low-dose sirolimus in patients given the same dose of MMF.

UGT genotype may contribute to adverse events following medication with mycophenolate mofetil in pediatric kidney transplant recipients

Leukopenia and diarrhea are the predominant adverse events associated with mycophenolate mofetil (MMF), leading to dose reduction or discontinuation in children. Polymorphisms of the drug's main metabolizing enzyme, uridine diphosphate-glucuronosyl transferase (UGT), confer alteration in drug exposure. We studied the incidence of these polymorphisms in pediatric kidney transplant recipients experiencing MMF-associated leukopenia and diarrhea. UGT genotypes of 16 affected children who recovered after MMF dose reduction or discontinuation were compared with those of 22 children who tolerated the drug at standard doses. DNA was extracted and sequenced using standard procedures to detect polymorphisms associated with increased (e.g., UGT1A9 -331T>C) or decreased drug exposure. All three patients who were homozygous for UGT1A9 -331T>C developed leukopenia, and heterozygotes also had significantly more toxicity (P = 0.04). A weaker association (P = 0.08) existed in UGT2B7 -900G>A carriers. Our data implicate UGT polymorphisms associated with altered drug exposure as potential predictors of MMF adverse events.

Multicenter evaluation of a new inosine monophosphate dehydrogenase inhibition assay for quantification of total mycophenolic acid in plasma

The performance characteristics of a new inosine monophosphate dehydrogenase inhibition assay for the quantification of total mycophenolic acid (MPA) in plasma (Roche Diagnostics) were assessed in a multicenter evaluation. Validation data were collected from four institutions. Within-run and total imprecision were acceptable (n = 21 for each of 7 materials, coefficients of variation ranging 0.7-9.6%). The lower limit of quantification was 0.31 mg/L. The assay was linear from 0.31 to 15.0 mg/L. Method comparison with validated high-performance liquid chromatography with ultraviolet light or liquid chromatography tandem mass spectrometry methods showed good agreement (coefficients of correlation 0.974-0.994, slopes 1.01-1.17, intercepts -0.17 to 0.06). There was no difference found between results from different transplant types (cardiac vs. renal) or comedications (cyclosporine vs. tacrolimus). The recovery of samples from a proficiency testing scheme was acceptable. The cross-reactivity of AcMPAG, an in vitro active metabolite of MPA, was examined by adding AcMPAG to a pool of patient samples and subsequent quantification. MPA overestimation by AcMPAG cross-reactivity was found to be low (<5%). Thus, this interference is expected to be clinically irrelevant. In conclusion, the Roche Total MPA assay is a promising alternative for MPA quantification where chromatographic methods are not available.

Calcineurin inhibitor sparing in paediatric solid organ transplantation : managing the efficacy/toxicity conundrum

Despite their efficacy, the calcineurin inhibitors (CNIs) ciclosporin and tacrolimus carry a risk of debilitating adverse effects, especially nephrotoxicity, that affect the long-term outcome and survival of children who are given organ transplants. Simple reduction in dosage of CNI has little or no long-term benefit on their adverse effects, and complete withdrawal without threatening graft outcome may only be possible after liver transplantation. Until the last decade, the only option was to increase corticosteroid and/or azathioprine doses, which imposed additional long-term hazards. Considered here are the emerging generation of new agents offering an opportunity for improving long-term graft survival, minimizing CNI-related adverse events and ensuring patient well-being.A holistic, multifaceted strategy may need to be considered - initial selection and optimized use and monitoring of immunosuppressant regimens, early recognition of indicators of patient and graft dysfunction, and, where applicable, early introduction of CNI-sparing regimens facilitating CNI withdrawal. The evidence reviewed here supports these approaches but remains far from definitive in paediatric solid organ transplantation. Because de novo immunosuppression uses CNI in more than 93% of patients, reduction of CNI-related adverse effects has focused on CNI sparing or withdrawal.A recurring theme where sirolimus and mycophenolate mofetil have been used for this purpose is the importance of their early introduction to limit CNI damage and provide long-term benefit: for example, long-term renal function critically reflects that at 1 year post-transplant. While mycophenolic acid shows advantages over sirolimus in preserving renal function because the latter is associated with proteinuria, sirolimus appears the more potent immunosuppressant but also impairs early wound healing. The use of CNI-free immunosuppressant regimens with depleting or non-depleting antibodies plus sirolimus and mycophenolic acid needs much wider investigation to achieve acceptable rejection rates and conserve renal function. The adverse effects of the alternative immunosuppressants, particularly the dyslipidaemia associated with sirolimus, needs to be minimized to avoid replacing one set of adverse effects (from CNIs) with another. While we can only conjecture that judicious combinations with the second generation of novel immunosuppressants currently in development will provide these solutions, a rationale of low-dose therapy with multiple immunosuppressants acting by complementary mechanisms seems to hold the promise for efficacy with minimal toxicity until the vision of tolerance achieves reality.