Current target ranges of mycophenolic acid exposure and drug-related adverse events: A 5-year, open-label, prospective, clinical follow-up study in renal allograft recipients

Mycophenolate Dose Reduction in Tacrolimus-based Regimens and Long-term Kidney Transplant Outcomes in Australia and New Zealand

Background

Mycophenolate dose reduction (MDR) is associated with acute rejection and transplant failure in kidney transplant recipients (KTRs). The optimal dose to prevent rejection and reduce complications remains poorly defined in tacrolimus-based regimens.

Methods

We assessed adult KTRs from 2005 to 2017 initiated on mycophenolate mofetil 2 g/d, tacrolimus, and prednisolone from the Australia and New Zealand Dialysis and Transplant Registry. KTRs with rejection within the first 30 d posttransplant were excluded. The primary outcome was time to first rejection between 30 d and 2 y posttransplant. Mycophenolate dose was modeled as a time-varying covariate using Cox proportional hazards regression. Secondary outcomes included assessment of early MDR to <1.5 g/d within the first 6 mo posttransplant and subsequent patient and death-censored graft survival.

Results

In the primary analysis, 3590 KTRs were included. Compared with mycophenolate dose of ≥2 g/d, both 1.0-<1.5 and <1 g/d were associated with an increased risk of rejection during the 2 y posttransplant (hazard ratio [HR] 1.67; 95% confidence interval [CI], 1.29-2.16; P < 0.001 and HR 2.06; 95% CI, 1.36-3.13; P = 0.001, respectively) but not 1.5-<2 g/d (HR 1.20; 95% CI, 0.94-1.53; P = 0.14). Early MDR to <1.5 g/d occurred in 45.3% of KTRs and was an independent risk factor for death-censored graft failure (HR 1.32; 95% CI, 1.05-1.66; P = 0.016) but not death (HR 1.18; 95% CI, 0.97-1.44; P = 0.10), during a median follow-up of 5.0 (interquartile range, 2.6-8.5) y.

Conclusions

Early MDR was a risk factor for subsequent rejection and graft failure in KTRs receiving contemporary tacrolimus-based regimens.

Evaluation of mycophenolic acid exposure in a patient with immune-related hepatotoxicity caused by nivolumab and ipilimumab therapy for malignant melanoma: a case report

BACKGROUND

Guidelines such as the National Comprehensive Cancer Network recommend mycophenolate mofetil (MMF) for the treatment of severe steroid-refractory immune-related hepatotoxicity. Mycophenolic acid (MPA) is an active form of MMF that suppresses T- and B-lymphocyte proliferation and immune-related adverse events caused by immune checkpoint inhibitors. MPA has a narrow therapeutic range (37-70 µg·h/mL) and overexposure increases the risk of leukopenia in transplantation. However, the optimal use of MMF in oncology has not yet been established; thus, monitoring plasma MPA concentrations is necessary to avoid excessive immunosuppression in oncology practice.

CASE PRESENTATION

We evaluated plasma MPA concentration in a 75-year-old man with immune-related hepatotoxicity following nivolumab and ipilimumab combination therapy for malignant melanoma. The patient developed severe hepatotoxicity after immunotherapy, and immunosuppressant therapy with corticosteroids was initiated. The patient then developed steroid-refractory immune-related hepatotoxicity; therefore, MMF (1,000 mg twice daily) was co-administered. Seven days after the administration of MMF, the plasma MPA concentration was measured using an enzyme multiplied immunoassay technique. The area under the plasma concentration-time curve for MPA from 0 to 12 h was 41.0 µg·h/mL, and the same dose of MMF was continued. Grade 2 lymphocytopenia, which could be attributed to MMF, was observed during the administration period. Unfortunately, the patient was infected with SARS-CoV-2 and died from respiratory failure.

CONCLUSION

Our patient did not exceed the upper limit of MPA levels as an index of the onset of side effects of kidney transplantation and achieved rapid improvement in liver function. Prompt initiation of MMF after assessment of the steroid effect leads to adequate MPA exposure. Therapeutic drug monitoring should be considered when MMF is administered, to avoid overexposure.

Influence of genetic polymorphisms on pharmacokinetics and treatment response of mycophenolic acid: a scoping review

This scoping review explores the impact of genetic polymorphisms on the pharmacokinetics and treatment responses of mycophenolic acid (MPA), an immunosuppressant. The study includes 83 articles from 1226 original studies, focusing on transplantation (n = 80) and autoimmune disorders (n = 3). Genetic variants in uridine 5'-diphospho-glucuronosyltransferase (UGT1A9, UGT1A8 and UGT2B7) and transmembrane transporters (ABCC2, SLCO1B1, SLCO1B3 and ABCB1) significantly affected MPA's pharmacokinetics and susceptibility to its adverse effect. Whereas variants in several genes including UGT1A9, UGT2B7, IMPDH1 and IMPDH2 have been associated with a higher risk of transplant rejection. However, there is a lack of studies on MPA's impact on autoimmune disorders and limited research on the Asian population. The findings underscore the need for further research on MPA's impact across different populations and diseases, particularly among other Asian ethnic groups, to advance personalized medicine in MPA therapy.

Mycophenolate Mofetil Dose Adjustment in Pediatric Kidney Transplant Recipients

BACKGROUND

The Immunosuppressant Bayesian Dose Adjustment web site aids clinicians and pharmacologists involved in the care of transplant recipients; it proposes dose adjustments based on the estimated area under the concentration-time curve (AUCs). Three concentrations (T 20 min , T 1 h , and T 3 h ) are sufficient to estimate mycophenolic acid (MPA) AUC 0-12 h in pediatric kidney transplant recipients. This study investigates mycophenolate mofetil (MMF) doses and MPA AUC values in pediatric kidney transplant recipients, and target exposure attainment when the proposed doses were followed, through a large-scale analysis of the data set collated since the inception of the Immunosuppressant Bayesian Dose Adjustment web site.

METHODS

In this study, 4051 MMF dose adjustment requests, corresponding to 1051 patients aged 0-18 years, were retrospectively analyzed. AUC calculations were performed in the back office of the Immunosuppressant Bayesian Dose Adjustment using published Bayesian and population pharmacokinetic models.

RESULTS

The first AUC request was posted >12 months posttransplantation for 41% of patients. Overall, only 50% had the first MPA AUC 0-12 h within the recommended 30-60 mg.h/L range. When the proposed dose was not followed, the proportion of patients with an AUC in the therapeutic range for MMF with cyclosporine or tacrolimus at the subsequent request was lower (40% and 45%, respectively) than when it was followed (58% and 60%, respectively): P = 0.08 and 0.006, respectively. Furthermore, 3 months posttransplantation, the dispersion of AUC values was often lower at the second visit when the proposed doses were followed, namely, P = 0.03, 0.003, and 0.07 in the 4 months-1 year, and beyond 1 year with <6-month or >6-month periods between both visits, respectively.

CONCLUSIONS

Owing to extreme interindividual variability in MPA exposure, MMF dose adjustment is necessary; it is efficient at reducing such variability when based on MPA AUC.

Immune Monitoring of Mycophenolate Mofetil Activity in Healthy Volunteers Using Ex Vivo T Cell Function Assays

Mycophenolate mofetil (MMF) is part of the standard immunosuppressive treatment after transplantation and usually given as "one-dose-fits-all" together with a calcineurin inhibitor (CNI). Although drug concentrations are frequently monitored, there is still a group of patients who experience side effects related to excessive or insufficient immune suppression. We therefore aimed to identify biomarkers that reflect the overall immune status of the patient and might support individualized dosing. We previously studied immune biomarkers for CNIs and aimed to investigate whether these are also suitable to monitor MMF activity. Healthy volunteers received a single dose of MMF or placebo, after which IMPDH enzymatic activity, T cell proliferation, and cytokine production were measured and compared to MPA (MMF's active metabolite) concentration in three different matrices (plasma, peripheral blood mononuclear cells, and T cells). MPA concentrations in T cells exceeded those in PBMCs, but all intracellular concentrations correlated strongly with plasma concentrations. At clinically relevant MPA concentrations, IL-2 and IFN-γ production was mildly suppressed, while MPA T cell proliferation was strongly inhibited. Based on these data, it is expected that monitoring of T cell proliferation in MMF-treated transplantation patients may be a valid strategy to avoid excessive immune suppression.

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.

Drug monitoring in systemic lupus erythematosus

Therapeutic drug monitoring (TDM) is not yet accepted by systemic lupus erythematosus (SLE) treatment guidelines. Studies in SLE, however, have proven benefit in three areas: identification of non-adherence or poor adherence; targets for clinical benefit; and ranges of toxicity. This review covers the data on three medications commonly used for SLE, drawing on studies from both the SLE and non-SLE literature.

Serum albumin level is associated with mycophenolic acid concentration in children with idiopathic nephrotic syndrome

Mycophenolate mofetil is effective for the treatment of pediatric idiopathic nephrotic syndrome (INS). The dosage of mycophenolate mofetil is adjusted according to the serum concentration of mycophenolic acid (MPA). Kidney function or cyclosporine (CsA) concentrations affect serum MPA levels. However, few studies have focused on the association between serum concentrations of MPA and albumin. This retrospective observational study aimed to evaluate the relationship between the serum concentrations of MPA and albumin in INS children. Subjects were children with INS who underwent the therapeutic drug monitoring of CsA and MPA. We obtained the serum albumin (sAlb) concentration, estimated glomerular filtration rate (eGFR), age, and MPA and CsA areas under concentration-time curves from 0 to 12 h (AUC_0-12). Multiple linear regression analysis and generalized estimating equations were performed to predict values for MPA AUC_0-12. We obtained information for 51 INS children with 261 MPA AUC_0-12 measurements. The standardized regression coefficients of sAlb, eGFR, CsA AUC_0-12, and age were 0.54, - 0.21, - 0.07, and 0.04, respectively. Furthermore, MPA AUC_0-12 levels positively correlated with sAlb concentrations (p < 0.001) and were inversely correlated with eGFR values (p = 0.005) but not with CsA AUC_0-12 (p = 0.24) and age (p = 0.65).Conclusion: Serum albumin concentration was strongly associated with total MPA concentration compared with kidney function or CsA values. Although patients with INS may have a low serum concentration of total MPA in the presence of low sAlb concentration, close attention should be paid to the interpretation of the low MPA values. What is Known: • The dosage of mycophenolate mofetil is adjusted according to the serum concentration of total mycophenolic acid. • Kidney function, cyclosporin concentrations, or serum albumin concentrations influence serum mycophenolic acid levels. What is New: • Serum albumin concentration is more strongly associated with total mycophenolic acid concentration than kidney function or cyclosporin values. • In children with nephrotic syndrome, the total mycophenolic acid concentration may not increase in the presence of severe hypoalbuminemia.

Associations among erythropoietic, iron-related, and FGF23 parameters in pediatric kidney transplant recipients

BACKGROUND

In pediatric kidney transplant recipients, anemia is common and oftentimes multifactorial. Hemoglobin concentrations may be affected by traditional factors, such as kidney function and iron status, as well as novel parameters, such as fibroblast growth factor 23 (FGF23).

METHODS

Here, we evaluated associations among erythropoietic, iron-related, and FGF23 parameters in a cohort of pediatric kidney transplant recipients, hypothesizing that multiple factors are associated with hemoglobin concentrations.

RESULTS

In a cross-sectional analysis of 59 pediatric kidney transplant recipients (median (interquartile range) age 16.3 (13.5, 18.6) years, median estimated glomerular filtration rate (eGFR) 67 (54, 87) ml/min/1.73 m²), the median age-related hemoglobin standard deviation score (SDS) was -2.1 (-3.3, -1.1). Hemoglobin SDS was positively associated with eGFR and calcium, and was inversely associated with erythropoietin (EPO), mycophenolate dose, and total, but not intact, FGF23. In multivariable analysis, total FGF23 remained inversely associated with hemoglobin SDS, independent of eGFR, iron parameters, EPO, and inflammatory markers, suggesting a novel FGF23-hemoglobin association in pediatric kidney transplant patients. In a subset of patients with repeat measurements, only delta hepcidin was inversely associated with delta hemoglobin SDS. Also, delta EPO positively correlated with delta erythroferrone (ERFE), and delta ERFE inversely correlated with delta hepcidin, suggesting a possible physiologic role for the EPO-ERFE-hepcidin axis in the setting of chronic kidney disease (CKD).

CONCLUSION

Our study provides further insight into factors potentially associated with erythropoiesis in pediatric kidney transplant recipients. A higher resolution version of the Graphical abstract is available as Supplementary information.

Effect of UGT polymorphisms on pharmacokinetics and adverse reactions of mycophenolic acid in kidney transplant patients

Mycophenolic acid (MPA) is a common immunosuppressive drug for kidney transplantation patients, and is characterized by a narrow therapeutic index and significant individual variability. UGTs are the main enzymes responsible for the metabolism of MPA. Although, many studies have focused on the relationship between UGT polymorphisms and pharmacokinetics and adverse reactions of MPA, the conclusion are controversial. We reviewed the relevant literature and summarized the significant influences of UGT polymorphisms, such as UGT1A8 (rs1042597, rs17863762), UGT1A9 (rs72551330, rs6714486, rs17868320, rs2741045, rs2741045) and UGT2B7 (rs7438135, rs7439366, rs7662029), on the pharmacokinetics of MPA and its metabolites and adverse reactions. The review provides a reference for guiding the individualized administration of MPA and reducing adverse reactions to MPA.

Effect of mycophenolic acid and tacrolimus on the incidence of infectious complications after kidney transplantation

INTRODUCTION

Infectious complications remain a common cause of mortality after kidney transplantation (KTx). Goal of effective immunosuppressive treatment (IS) must be balanced between decreasing incidence of acute kidney rejection (AKR) and avoiding the incidence of infections, at the same time.

MATERIALS AND METHODS

The aim of our analysis was to identify the risk of fixed daily dose (DD) of mycophenolic acid (MPA) and levels of tacrolimus (TAC) in the development of a single, recurrent infection and AKR after KTx.

RESULTS

Our analysis consisted of 100 patients after KTx (66 males, 34 females). MPA DD > 1080 mg was a risk factor (RF) for recurrent infection in general (OR 1.2964;P = 0.0277), for recurrent bacterial infection from 1^st to 6^th month (OR 1.2674;P = 0.0151), recurrent bacterial infection (OR 1.2574;P = 0.0436), single viral infection (OR 1.2640;P = 0.0398) from 6^th-12^th month after KTx. MPA DD > 1080 mg and levels of TAC above recommended levels were not independent RF for the incidence of the infection.

CONCLUSION

MPA DD > 1080 mg as a RF for recurrent infection starting in the 1^st month after KTx with significant association between the incidence of infections and MPA DD and TAC levels, without increased risk of AKR. In the centers with fixed dosing of IS, this can lead to lowering the risk of infections by decreasing MPA DD 1 month after KTx without increasing risk of infections.

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

ABSTRACT

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

Therapeutic drug monitoring of mycophenolate mofetil in pediatric patients: novel techniques and current opinion

Introduction: Mycophenolate mofetil (MMF) is an ester prodrug of the immunosuppressant mycophenolic acid (MPA) and is recommended and widely used for maintenance immunosuppressive therapy in solid organ and stem-cell transplantation as well as in immunological kidney diseases. MPA is a potent, reversible, noncompetitive inhibitor of the inosine monophosphate dehydrogenase (IMPDH), a crucial enzyme in the de novo purine synthesis in T- and B-lymphocytes, thereby inhibiting cell-mediated immunity and antibody formation. The use of therapeutic drug monitoring (TDM) of MMF is still controversial as outcome data of clinical trials are equivocal. Areas covered: This review covers in great depth the existing literature on TDM of MMF in the field of pediatric (kidney) transplantation. In addition, the relevance of TDM in immunological kidney diseases, in particular childhood nephrotic syndrome is highlighted. Expert opinion: TDM of MMF has the potential to optimize therapy in pediatric transplantation as well as in nephrotic syndrome. Limited sampling strategies to estimate MPA exposure increase its feasibility. Future perspectives rather encompass approaches reflecting total immunosuppressive load than single drug TDM.

Pharmacodynamic assessment of mycophenolic acid in resting and activated target cell population during the first year after renal transplantation

Aims

To explore the pharmacodynamics of mycophenolic acid (MPA) through inosine monophosphate dehydrogenase (IMPDH) capacity measurement and purine levels in peripheral blood mononuclear cells (PBMC) longitudinally during the first year after renal transplantation (TX).

Methods

PBMC were isolated from renal recipients 0–4 days prior to and 6–9 days, 5–7 weeks and 1 year after TX (before and 1.5 hours after dose). IMPDH capacity and purine (guanine and adenine) levels were measured in stimulated and nonstimulated PBMC.

Results

Twenty‐nine patients completed the follow‐up period, of whom 24 received MPA. In stimulated PBMC, the IMPDH capacity (pmol 10⁻⁶ cells min⁻¹) was median (interquartile range) 127 (95.8–147) before TX and thereafter 44.9 (19.2–93.2) predose and 12.1 (4.64–23.6) 1.5 hours postdose across study days after TX. The corresponding IMPDH capacity in nonstimulated PBMC was 5.71 (3.79–6.93), 3.35 (2.31–5.62) and 2.71 (1.38–4.08), respectively. Predose IMPDH capacity in nonstimulated PBMC increased with time, reaching pre‐TX values at 1 year. In stimulated PBMC, both purines were reduced before (median 39% reduction across days after TX) and after (69% reduction) dose compared to before TX. No alteration in the purine levels was observed in nonstimulated PBMC. Patients needing dose reductions during the first year had lower pre‐dose IMPDH capacity in nonstimulated PBMC (1.87 vs 3.00 pmol 10⁻⁶ cells min⁻¹, P = .049) at 6–9 days.

Conclusion

The inhibitory effect of MPA was stronger in stimulated PBMC. Nonstimulated PBMC became less sensitive to MPA during the first year after TX. Early IMPDH capacity appeared to be predictive of dose reductions.

Comparative Evaluation of Median Versus Youden Index Dichotomization Methods: Exposure-Response Analysis of Mycophenolic Acid and Acyl-Glucuronide Metabolite

BACKGROUND AND OBJECTIVES

Dichotomization of pharmacokinetic exposure measures in exposure-response relationship studies provides results that are interpretable in clinical care. Several methods exist in the literature on how to define the cut-off values needed for the dichotomization process. Commonly, the sample median is utilized to define the dichotomizing value; however, statistical methods based on the exposure metric and its association with the outcome are argued to result in a more proper definition of the optimal cut-point. The Youden index is a recommended statistical method to define the cut-off value. The current analysis objective is to compare the dichotomization results based on the Youden index versus median methods.

METHODS

Utilizing mycophenolic acid (MPA) exposure data and its related acute rejection and leukopenia outcome variables, the current study compared the MPA exposure-response relationship outcomes when MPA exposure is dichotomized via the Youden index versus median methods. Univariate logistic models were utilized to quantify the relationships between MPA exposure, including total MPA, unbound MPA, and the acyl-glucuronide metabolite of MPA, and the probabilities of acute rejection and leukopenia.

RESULTS

The overall trend of the results of the logistic models demonstrated a general similarity in the inferred exposure-response associations when considering either the Youden index-based or the median-based dichotomization methods.

CONCLUSION

The results demonstrated in this analysis suggest that both the Youden index and the median methods provide similar conclusions when dichotomization of a continuous variable is considered. However, confirmation of these conclusions comes from future powered studies that include a larger number of subjects.

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.

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 (AUC0-12h ) 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 AUC0-12h 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 AUC0-12h 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 AUC0-12h to mycophenolic acid AUC0-12h 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.

Tofacitinib Halts Progression of Graft Dysfunction in a Rat Model of Mixed Cellular and Humoral Rejection

BACKGROUND

The progression from acute to chronic antibody-mediated rejection in kidney transplant recipients is usually not prevented by current therapeutic options. Here, we investigated whether the use of tofacitinib (TOFA), a Janus kinase 3 inhibitor, was capable of preventing the progression of allograft dysfunction in a Fisher-to-Lewis rat model of kidney transplantation.

METHODS

Rats were treated from the third week after transplantation to allow the development of rejection. Treatment was based on cyclosporin A, rapamycin or TOFA. Renal function was assessed at 1, 4, 8, and 12 weeks after transplantation, whereas rat survival, histological lesions, and infiltrating lymphocytes were analyzed at 12 weeks.

RESULTS

Tofacitinib prolonged graft survival, preserved tubular and glomerular structures and reduced humoral damage characterized by C4d deposition. Tofacitinib was able to reduce donor-specific antibodies. In addition, T and natural killer cell graft infiltration was reduced in TOFA-treated rats. Although rapamycin-treated rats also showed prolonged graft survival, glomerular structures were more affected. Moreover, only TOFA treatment reduced the presence of T, B and natural killer cells in splenic parenchyma.

CONCLUSIONS

Tofacitinib is able to reduce the immune response generated in a rat model of kidney graft rejection, providing prolonged graft and recipient survival, better graft function, and less histological lesions.

Long-term desensitization for ABO-incompatible living related kidney transplantation recipients with high refractory and rebound anti-blood type antibody: case report

Background

ABO-incompatible living related kidney transplantation (ABO-iLKT) has increased the possibilities for kidney transplantation in patients with end stage renal disease. Due to advancements in immunosuppressive agents and the identification of immunological conditions following ABO-iLKT, this transplantation technique has achieved the same success rate as ABO-compatible LKT. However, some patients continue to generate anti-blood type antibodies, despite conventional immunosuppressant treatment.

Case presentation

A 60-year-old man was referred to our hospital for kidney transplantation. The proposed transplant was ABO incompatible, from a donor with blood-type A to a recipient with blood-type O. The recipient’s anti-A blood-type IgG antibody titer was measured at 4096-fold dilution. Following desensitization therapy, including mycophenolate mofetil (MMF) 750 mg/day for 3 months, intravenous Rituximab 200 mg, and two sessions of double filtration plasmapheresis, the anti-A blood-type IgG antibody titer decreased to only 516-fold dilution and did not meet our target of less than 128-fold dilution. MMF was thus continued for an additional 4 months and four additional sessions of plasmapheresis were undertaken. Following these interventions, antibody titers decreased to 128-fold dilution and ABO-iLKT was performed. Following transplant, antibody-mediated rejection was not observed and renal function was preserved. However, a post-operative renal biopsy 1.5 months later showed evidence of T-cell-mediated rejection IB. The patient was treated with steroids, with no increase in serum creatinine.

Conclusion

Our findings suggest that the long-term single MMF desensitization therapy could be a suitable option for ABO-iLKT with high refractory and rebound anti-blood type antibody. Further studies are required to establish the optimal immunosuppression regimen to control B cell- mediated immunity in ABO-iLKT.

Differential profiles of adverse events associated with mycophenolate mofetil between adult and pediatric renal transplant patients

Objective

Immunosuppressive regimens after renal transplantation usually include a combination of calcineurin inhibitors, corticosteroids, and a proliferation inhibitor, either azathioprine or mycophenolate mofetil (MMF), to prevent rejection and maintain graft function. MMF has a stronger immunosuppressive effect than does azathioprine. This study aimed to examine MMF-associated adverse events in renal transplant patients.

Methods

Retrospective pharmacovigilance disproportionality analysis was conducted using the Japanese Adverse Drug Event Report database.

Results

A total of 11,594 adverse drug events were reported in renal transplant patients; 10,272 (88.6%) involved adults and 1322 (11.4%) involved children. In adult patients, the most frequent adverse events induced by MMF were cytomegalovirus infection (272 reports), urinary tract infection (69 reports), and polyomavirus-associated nephropathy (61 reports). Among adverse events, the highest reporting odds ratio (ROR) was found for cytomegalovirus infection (ROR, 1.58; 95% confidence interval, 1.36–1.83). In pediatric patients, the rank order for MMF-associated adverse events was cytomegalovirus infection (27 reports), bronchitis (23 reports), and cytomegalovirus viremia (19 reports), but these adverse events were not detected as a signal.

Conclusion

Our results show the safety profile of MMF in pediatric renal transplant patients. These findings can be used to update information used for prescriptions for pediatric patients.

SNPs affecting the clinical outcomes of regularly used immunosuppressants

Recent studies have suggested that genomic diversity may play a key role in different clinical outcomes, and the importance of SNPs is becoming increasingly clear. In this article, we summarize the bioactivity of SNPs that may affect the sensitivity to or possibility of drug reactions that occur among the signaling pathways of regularly used immunosuppressants, such as glucocorticoids, azathioprine, tacrolimus, mycophenolate mofetil, cyclophosphamide and methotrexate. The development of bioinformatics, including machine learning models, has enabled prediction of the proper immunosuppressant dosage with minimal adverse drug reactions for patients after organ transplantation or for those with autoimmune diseases. This article provides a theoretical basis for the personalized use of immunosuppressants in the future.

Estimation of Mycophenolic Acid Area Under the Curve With Limited-Sampling Strategy in Chinese Renal Transplant Recipients Receiving Enteric-Coated Mycophenolate Sodium

BACKGROUND

The enteric-coated mycophenolate sodium (EC-MPS), whose active constituent is mycophenolic acid (MPA), has been widely clinically used for organ transplant recipients. However, its absorption is delayed due to its special designed dosage form, which results in difficulty to monitor the exposure of the MPA in patients receiving the EC-MPS. This study was aimed at developing a relatively practical and precise model with limited sampling strategy to estimate the 12-hour area under the concentration-time curve (AUC0-12 h) of MPA for Chinese renal transplant recipients receiving EC-MPS.

METHODS

A total of 36 Chinese renal transplant recipients receiving the EC-MPS and tacrolimus were recruited in this study. The time point was 2 weeks after the transplantation for all the patients. The MPA concentrations were measured with enzyme-multiplied immunoassay technique for 11 blood specimens collected predose and at 0.5, 1, 1.5, 2, 2.5, 3, 4, 6, 8, and 12 hours after the morning dose of EC-MPS. The measured AUC was calculated with these 11 points of MPA concentrations with the linear trapezoidal rule. Limited sampling strategy was used to develop models for estimated AUC in the model group (n = 18). The bias and precision of different models were evaluated in the validation group (n = 18).

RESULTS

C4 showed the strongest correlation with the measured AUC. The best 3 time point equation was 6.629 + 8.029 × C0 + 0.592 × C3 + 1.786 × C4 (R = 0.910; P < 0.001), whereas the best 4 time point equation was 3.132 + 5.337 × C0 + 0.735 × C3 + 1.783 × C4 + 3.065 × C8 (R = 0.959; P < 0.001). When evaluated in the validation group, the 4 time point model had a much better performance than the 3 time point model: for the 4 time point model: R = 0.873, bias = 0.505 [95% confidence interval (CI), -10.159 to 11.170], precision = 13.370 (95% CI, 5.186-21.555), and 77.8% of estimated AUCs was within 85%-115% of the measured AUCs; for the 3 time point model: R = 0.573, bias = 6.196 (95% CI, -10.627 to 23.018), precision = 21.286 (95% CI, 8.079-34.492), and 50.0% of estimated AUCs was within 85%-115% of the measured AUCs.

CONCLUSIONS

It demanded at least 4 time points to develop a relatively reliable model to estimate the exposure of MPA in renal transplant recipients receiving the EC-MPS. The long time span needed restricted its application, especially for the outpatients, but it could be a useful tool to guide the personalized prescription for the inpatients.

Mycophenolate mofetil-related leukopenia in children and young adults following kidney transplantation: Influence of genes and drugs

MMF is commonly prescribed following kidney transplantation, yet its use is complicated by leukopenia. Understanding the genetics mediating this risk will help clinicians administer MMF safely. We evaluated 284 patients under 21 years of age for incidence and time course of MMF-related leukopenia and performed a candidate gene association study comparing the frequency of 26 SNPs between cases with MMF-related leukopenia and controls. We matched cases by induction, steroid duration, race, center, and age. We also evaluated the impact of induction and SNPs on time to leukopenia in all cases. Sixty-eight (24%) patients had MMF-related leukopenia, of which 59 consented for genotyping and 38 were matched with controls. Among matched pairs, no SNPs were associated with leukopenia. With non-depleting induction, UGT2B7-900A>G (rs7438135) was associated with increased risk of MMF-related leukopenia (P = .038). Time to leukopenia did not differ between patients by induction agent, but 2 SNPs (rs2228075, rs2278294) in IMPDH1 were associated with increased time to leukopenia. MMF-related leukopenia is common after transplantation. UGT2B7 may influence leukopenia risk especially in patients without lymphocyte-depleting induction. IMPDH1 may influence time course of leukopenia after transplant.

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

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

Anesthetic Considerations in Transplant Recipients for Nontransplant Surgery

As solid organ transplantation increases and patient survival improves, it will become more common for these patients to present for nontransplant surgery. Recipients may present with medical problems unique to the transplant, and important considerations are necessary to keep the transplanted organ functioning. A comprehensive preoperative examination with specific focus on graft functioning is required, and the anesthesiologist needs pay close attention to considerations of immunosuppressive regimens, blood product administration, and the risk benefits of invasive monitoring in these immunosuppressed patients. This article reviews the posttransplant physiology and anesthetic considerations for patients after solid organ transplantation.

Predicting therapy response to mycophenolic acid using UGT1A9 genotyping: towards personalized medicine in atopic dermatitis

Atopic dermatitis (AD) is a very common chronic inflammatory skin disease requiring long-term treatment. Mycophenolic acid (MPA) is used off-label in treatment of patients with severe AD failing Cyclosporin A (CsA) treatment, however clinical efficacy is observed in only half of the AD patients. In blood, MPA levels are known to have a large interindividual variability. Low MPA exposure and increased enzyme activity correlates with the presence of UGT1A9 polymorphisms. In this retrospective study, 65 adult AD patients treated with MPA were classified as responder or non-responder to MPA treatment. UGT1A9 polymorphisms were determined using PCR. A significantly higher number of UGT1A9 polymorphisms was found in the group that did not respond to MPA treatment. Of the patients that carried a UGT1A9 polymorphism, 85.7% were non-responsive to MPA treatment. This implies that non-responsiveness in AD patients is more likely to occur in carriers of a UGT1A9 polymorphism. In a binary logistic regression analysis the odds ratio (OR) was 8.65 (95% confidence interval: 0.93-80.17). Our results show that UGT1A9 polymorphisms can be used to identify patients with non-responsiveness to MPA. Patients with UGT1A9 polymorphisms might benefit from higher MPA dosage.

Therapeutic drug monitoring of enteric-coated mycophenolate sodium by limited sampling strategies is associated with a high rate of failure

Background

Therapeutic drug monitoring of mycophenolic acid (MPA) is usually performed with a limited sampling strategy (LSS), which relies on a limited number of blood samples and subsequent extrapolation of the global exposure to MPA. LSS is usually performed successfully with mycophenolate mofetil (MMF), but data on enteric-coated mycophenolate sodium (EC-MPS) are scarce. Here, we evaluated the feasibility of 6-h LSS therapeutic drug monitoring with EC-MPS compared with MMF monitoring among kidney transplant recipients.

Methods

Sixty-two patients who received EC-MPS during the first 6 months of transplantation were compared with a matched group of 64 MMF-treated kidney transplant recipients. The area under the curve (AUC) was computed by LSS using multiple concentration time points (0, 1, 2, 3 and 6 h post-dose) and a trapezoidal rule. Patients had MPA therapeutic drug monitoring performed on two occasions, one within 2 weeks and the second after 3–4 months of transplantation.

Results

EC-MPS monitoring and MMF therapeutic drug monitoring were not interpretable in 34.5% (n = 40/116) and 1.8% (n = 2/112) of patients, respectively {relative risk [RR] 19.3 [95% confidence interval (CI) 4.8–78.0]; P < 0.0001}. The main cause of abnormal EC-MPS therapeutic drug monitoring was delayed absorption of both the previous evening and the morning dose, resulting in MPA plasma levels before the next morning dose being higher than MPA plasma levels measured at 1, 2 and 3 h after taking EC-MPS. Cyclosporin in association with MMF significantly increased the risk of low AUC values (<30 mg h/L) in comparison with tacrolimus [55% (n = 11/20) and 10% (n = 9/88), respectively; RR 5.4 (95% CI 2.6–11.2); P < 0.0001].

Conclusions

The risk of therapeutic drug monitoring failure with EC-MPS is >30% during the first 6 months of renal transplantation. Delayed pharmacokinetics was the main reason. In contrast, the risk of therapeutic drug monitoring failure was substantially lower with MMF.

Unmet medical needs in lupus nephritis: solutions through evidence-based, personalized medicine

Lupus nephritis (LN) remains a kidney disease with significant unmet medical needs despite extensive clinical and translational research over the past decade. These include the need to (i) predict the individual risk for LN in a patient with systemic lupus erythematosus, (ii) identify the best therapeutic option for an individual patient, (iii) distinguish chronic kidney damage from active immunologic kidney injury, (iv) develop efficient treatments with acceptable or no side effects and improve the design of randomized clinical trials so that effective drugs demonstrate efficacy. This review discusses the underlying reasons for these unmet medical needs and options of how to overcome them in the future.

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).

Replacement of mycophenolate acid with everolimus in patients who became neutropenic after renal transplant

OBJECTIVES

Neutropenia after kidney transplant is an adverse event usually treated with a dosage reduction of mycophenolic acid. We evaluated the efficacy and safety of substituting mycophenolic acid with everolimus in patients with persistent neutropenia after kidney transplant.

MATERIALS AND METHODS

This study was a retrospective analysis. A total of 17 patients who were initially treated with mycophenolic acid (1912 ± 196 mg/d), calcineurin inhibitors, and methylprednisolone for kidney transplant were included.

RESULTS

In 15 patients, neutropenia occurred within the first 3 months (during valganciclovir administration), and in 2 patients between the fourth and sixth month after transplant. One hundred eighteen episodes of neutropenia were recorded, originally treated by reducing the dosage of mycophenolic acid (765 ± 390 mg/d) and administering granulocyte colony-stimulating factor. Three patients experienced acute rejection 5 to 10 days after reducing the dosage of mycophenolic acid, and they were successfully treated with pulse steroids. Five patients developed cytomegalovirus infection 108 ± 65 days after the onset of neutropenia. After replacing mycophenolic acid with everolimus, episodes of neutropenia were observed in 6 patients. In 1 patient, discontinuing everolimus was necessary after 1.5 months of treatment. In 5 patients with cytomegalovirus infection, neutropenia subsided after termination of valganciclovir treatment. In the remaining 11 patients, no episodes of neutropenia were observed. No episodes of acute rejection occurred, and renal function remained stable during a followup of 47 ± 30 months (estimated glomerular filtration rate [eGFRMDRD6]: 45 ± 14 mL/min/1.73 m2→47 ± 22 mL/min/1.73 m2].

CONCLUSIONS

Replacing mycophenolic acid with everolimus appears to be a safe and effective alternative treatment in neutropenic renal transplant recipients.

Associations between polymorphisms in target, metabolism, or transport proteins of mycophenolate sodium and therapeutic or adverse effects in kidney transplant patients

OBJECTIVES

Different associations between single nucleotide polymorphisms (SNPs) in cellular target, metabolism enzymes or transport proteins, and biopsy-proven acute rejection (BPAR) or adverse events have been reported in transplant patients receiving mycophenolate mofetil. This work aimed to study these in patients on enteric-coated mycophenolate sodium (EC-MPS).

PATIENTS AND METHODS

The study included 189 renal transplant patients from the DOMINOS trial. Fifteen SNPs in IMPDH2, IMPDH1, ABCC2, SLCO1B3, UGT1A8, UGT1A9, UGT2B7, CYP2C8, HUS1, and IL12A were genotyped in all patients. Associations between SNPs and the first event of BPAR or diarrhea were investigated using multivariate logistic regressions. Associations between SNPs and leukopenia or anemia at nine different visits between days 0 and 190 after transplantation were studied using time-dependent Cox proportional hazards regression models.

RESULTS

Multivariate analyses showed that the CYP2C8 rs11572076 wild-type genotype was associated significantly with a lower risk of leukopenia [GG vs. GA: hazard ratio (95% confidence interval) 0.14 (0.03, 0.59), P=0.00783]. Higher EC-MPS doses and the UGT2B7 c.-840 G>A variant allele were associated with an increased risk of anemia [EC-MPS per unit dose increase: 1.004 (1.003, 1.005), P<0.0001; UGT2B7 GA vs. AA: 1.65 (1.12, 2.43), P=0.01043; GG vs. AA: 1.88 (1.23, 2.88), P=0.00343]. However, no significant association was found between any of the SNPs studied and diarrhea or BPAR.

CONCLUSION

Two pharmacogenetic associations reported previously with mycophenolate mofetil were found in a population of 189 renal transplant patients treated with EC-MPS.

Short-term therapeutic drug monitoring of mycophenolic acid reduces infection: a prospective, single-center cohort study in Chinese living-related kidney transplantation

BACKGROUND

The role of therapeutic drug monitoring (TDM) of mycophenolic acid (MPA) in kidney transplant recipients (KTRs) is not clear. We performed a prospective cohort study to evaluate the efficiency of MPA TDM in the Chinese population.

METHODS

A total of 183 living-related KTRs were studied; 101 KTRs received controlled-dose mycophenolate mofetil (MMF) (the CD group), and 82 patients received fixed-dose MMF (the FD group). MPA exposure was measured at days 3, 7, 14, and 30 in the CD group, and at day 30 in the FD group. The primary endpoint was treatment failure (a composite of acute rejection, graft loss, death, or MMF discontinuation) at 12 months post transplantation.

RESULTS

In the CD group, with a starting MMF dose of 2 g/day, approximately 35% of patients had high MPA levels, which were >60 mg × h/L, and mean MPA levels were 59.17 mg × h/L and 61.38 mg × h/L for the CD and FD groups, respectively (P = 0.588). After adjusting MMF dose, MPA exposures in the CD group at day 30 were lower than those in the FD group at day 30 (54.06 vs. 61.38, P = 0.004). At month 12, the CD group had fewer infections (16.8% vs. 31.7%, P = 0.018) with no difference in treatment failure, acute rejection, diarrhea, or anemia.

CONCLUSIONS

KTRs can benefit from short-term TDM of MPA in reducing infection, without increasing acute rejection.

Anemia control in kidney transplant recipients using once-monthly continuous erythropoietin receptor activator: a prospective, observational study

In a multicenter, prospective, observational study of 279 kidney transplant recipients with anemia, the efficacy and safety of once-monthly continuous erythropoietin receptor activator (C.E.R.A.) were assessed to a maximum of 15 months. The main efficacy variable was the proportion of patients achieving a hemoglobin level of 11-12 g/dL at each of visits between months 7 and 9. At study entry, 224 patients (80.3%) were receiving erythropoiesis stimulating agent (ESA) therapy including darbepoetin alfa (98), epoetin beta (61), and C.E.R.A. (45). The mean (SD) time between C.E.R.A. applications was 34.0 (11.9) days. Among 193 patients for whom efficacy data were available, mean (SD) hemoglobin was 11.1 (0.99) g/dL at study entry, 11.5 (1.1) g/dL at month 7, 11.6 (1.3) g/dL at month 9, and 11.4 (1.1) g/dL at month 15. During months 7–9, 20.7% of patients had all hemoglobin values within the range 11-12 g/dL and 64.8% were within 10–13 g/dL. Seven patients (2.5%) discontinued C.E.R.A. due to adverse events or serious adverse events. In this observational trial under real-life conditions, once-monthly C.E.R.A. therapy achieved stable hemoglobin levels in stable kidney transplant recipients with good tolerability, and with no requirement for any dose change in 43% of patients.

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.

Genes and beans: pharmacogenomics of renal transplant

Advances in the management of patients after solid organ transplantation have led to dramatic decreases in rates of acute rejection, but long-term graft and patient survival have remained unchanged. Individualized therapy after transplant will ideally provide adequate immunosuppression while limiting the adverse effects of drug therapy that significantly impact graft survival. Therapeutic drug monitoring represents the best approximation of individualized drug therapy in transplant at this time; however, obtaining pharmacogenomic data in transplant patients has the potential to enhance our current practice. Polymorphisms of target genes that impact pharmacokinetics have been identified for most immunosuppressants, including tacrolimus, cyclosporine, mycophenolate, azathioprine and sirolimus. In the future, pre-emptive assessment of a patient's genetic profile may inform drug selection and provide information on specific doses that will improve efficacy and limit toxicity.

Pharmacogenetics in solid organ transplantation: genes involved in mechanism of action and pharmacokinetics of immunosuppressive drugs

Allogenic solid organ transplantation has become the routine procedure in patients with end stage organ disease. Although the transplanted organ compensates deficient body functions, its allogenic nature requires institution of immune tolerance, nowadays provided by immunosuppressive drug administration. Both the safety and efficacy of immunosuppressive treatment depend on many factors, and maintaining levels of immunosuppressants within therapeutic range is the essential target for success in graft function preservation. It is obvious that drug and metabolite concentrations depend on efficiency of individual patient metabolism. Recently, many studies were undertaken to investigate the relationship between genetic factors, drug pharmacokinetics and therapy outcome, and interindividual variability apparently can be explained, at least in part, by genetically determined polymorphisms of xenobiotic-metabolizing enzymes, transport proteins and also in some cases, drug targets. This review presents the recent state of knowledge in the field of pharmacogenetics related to solid organ transplantation.

Blood disorders after kidney transplantation

Post transplant anemia (PTA) is a common issue in kidney transplant recipients. Most importantly it is associated with an impaired allograft function. Other important factors associated with PTA are immunosuppressive drugs (MPA, AZA and SRL), iron deficiency, infections (Parvo B19), older donor age, rejection episodes, an increased inflammatory state, and erythropoietin hyporesponsiveness. As there are no adequately powered RCTs in the kidney transplant population on anemia treatment with ESA, we have to rely on what we know from the large RCTs in the CKD population. The recently published KDIGO guidelines do not recommend treatment with ESA if Hb is >10 g/dl. Repletion of iron stores is emphasized. Post transplant leukopenia (PTL) and thrombocytopenia (PTT) are frequent complications especially in the first six months after kidney transplantation. Myelosuppression caused by immunosuppressive agents (MPA, AZA, SRL, rATG), antimicrobial drugs (VGCV), and CMV infection is the predominant cause. There are no widely accepted guidelines on treatment strategies, but most often dose reduction or discontinuation of causative medication is done. Most clinicians tend to decrease MPA dose, but this is eventually associated with an increase in acute rejection episodes. VGCV dose reduction (preemptive treatment instead of CMV prophylaxis) may be a successful strategy. In severe cases G-CSF treatment is an important management option and seems to be safe.

Effect of mycophenolate mofetil on hematological side effects incidence in renal transplant recipients

Mycophenolate mofetil (MMF), an immunosuppressant administered after solid organ transplantation, is generally well tolerated; however, it frequently causes hematological toxicity. In this study, we aimed to assess the relation between the pharmacokinetic parameters of MMF metabolites (mycophenolic acid [MPA] and 7-O-MPA glucuronide [MPAG]) and the adverse effects on the hematopoietic system in renal transplant recipients. The four-h pharmacokinetic profiles of MPA and MPAG were determined using the HPLC method for MMF-treated patients (n = 61) among 106 renal transplant recipients (during the late post-transplant period) participating in the study. Anemia was more frequently observed in the study group compared with the control group (30.7% vs. 20.0%) and although the difference was insignificant, plasma iron concentrations were significantly higher in patients treated with MMF (32.9 ± 9.4 μmol/L vs. 28.7 ± 9.4 μmol/L; p = 0.032). Iron supplementation was more frequently applied to patients with anemia (48.2%) compared with patients with hemoglobin within the norm (20.3%; p = 0.005). As all MPAG pharmacokinetic parameters correlated negatively with hemoglobin and hematocrit, and MPAG pharmacokinetic parameters were higher in patients with anemia, MPAG may be the predicting factor of MMF side effects. In renal transplant recipients, especially with deteriorated renal function, extensive iron supplementation may be ineffective as anemia was associated with declined renal function and was not caused by low iron concentration.