Mycophenolic Acid Exposure Research Articles

Targeted delivery of mycophenolic acid to the mesenteric lymph node using a triglyceride mimetic prodrug approach enhances gut-specific immunomodulation in mice

The mesenteric lymph nodes (MLN) are a key site for the generation of adaptive immune responses to gut-derived antigenic material and immune cells within the MLN contribute to the pathophysiology of a range of conditions including inflammatory and autoimmune diseases, viral infections, graft versus host disease and cancer. Targeting immunomodulating drugs to the MLN may thus be beneficial in a range of conditions. This paper investigates the potential benefit of targeting a model immunosuppressant drug, mycophenolic acid (MPA), to T cells in the MLN, using a triglyceride (TG) mimetic prodrug approach. We confirmed that administration of MPA in the TG prodrug form (MPA-TG), increased lymphatic transport of MPA-related species 83-fold and increased MLN concentrations of MPA >20 fold, when compared to MPA alone, for up to 4 h in mice. At the same time, the plasma exposure of MPA and MPA-TG was similar, limiting the opportunity for systemic side effects. Confocal microscopy and flow cytometry studies with a fluorescent model prodrug (Bodipy-TG) revealed that the prodrug accumulated in the MLN cortex and paracortex at 5 and 10 h following administration and was highly associated with B cells and T cells that are found in these regions of the MLN. Finally, we demonstrated that MPA-TG was significantly more effective than MPA at inhibiting CD4+ and CD8+ T cell proliferation in the MLN of mice in response to an oral ovalbumin antigen challenge. In contrast, MPA-TG was no more effective than MPA at inhibiting T cell proliferation in peripheral LN when mice were challenged via SC administration of ovalbumin. This paper provides the first evidence of an in vivo pharmacodynamic benefit of targeting the MLN using a TG mimetic prodrug approach. The TG mimetic prodrug technology has the potential to benefit the treatment of a range of conditions where aberrant immune responses are initiated in gut-associated lymphoid tissues.

Population pharmacokinetics of mycophenolic acid in paediatric patients.

Mycophenolic acid (MPA) is widely used in paediatric kidney transplant patients and sometimes prescribed for additional indications. Population pharmacokinetic or pharmacodynamic modelling has been frequently used to characterize the fixed, random and covariate effects of MPA in adult patients. However, MPA population pharmacokinetic data in the paediatric population have not been systematically summarized. The objective of this narrative review was to provide an up-to-date critique of currently available paediatric MPA population pharmacokinetic models, with emphases on modelling techniques, pharmacological findings and clinical relevance. PubMed and EMBASE were searched from inception of database to May 2020, where a total of 11 studies have been identified representing kidney transplant (n = 4), liver transplant (n = 1), haematopoietic stem cell transplant (n = 1), idiopathic nephrotic syndrome (n = 2), systemic lupus erythematosus (n = 2), and a combined population consisted of kidney, liver and haematopoietic stem cell transplant patients (n = 1). Critical analyses were provided in the context of MPA absorption, distribution, metabolism, excretion and bioavailability in this paediatric database. Comparisons to adult patients were also provided. With respect to clinical utility, Bayesian estimation models (n = 6) with acceptable accuracy and precision for MPA exposure determination have also been identified and systematically evaluated. Overall, our analyses have identified unique features of MPA clinical pharmacology in the paediatric population, while recognizing several gaps that still warrant further investigations. This review can be used by pharmacologists and clinicians for improving MPA pharmacokinetic-pharmacodynamic modelling and patient care.

Early prognostic performance of miR155-5p monitoring for the risk of rejection: Logistic regression with a population pharmacokinetic approach in adult kidney transplant patients.

Previous results from our group and others have shown that urinary pellet expression of miR155-5p and urinary CXCL-10 production could play a key role in the prognosis and diagnosis of acute rejection (AR) in kidney transplantation patients. Here, a logistic regression model was developed using NONMEM to quantify the relationships of miR155-5p urinary expression, CXCL-10 urinary concentration and tacrolimus and mycophenolic acid (MPA) exposure with the probability of AR in adult kidney transplant patients during the early post-transplant period. Owing to the contribution of therapeutic drug monitoring to achieving target exposure, neither tacrolimus nor MPA cumulative exposure was identified as a predictor of AR in the studied population. Even though CXCL-10 urinary concentration showed a trend, its effect on AR was not significant. In contrast, urinary miR155-5p expression was prognostic of clinical outcome. Monitoring miR155-5p urinary pellet expression together with immunosuppressive drug exposure could be very useful during routine clinical practice to identify patients with a potential high risk of rejection at the early stages of the post-transplant period. This early risk assessment would allow for the optimization of treatment and improved prevention of AR.

Only Modest Effect of Lipids and Albumin on Apparent Mycophenolic Acid Clearance in Pediatric Transplant Recipients – a Retrospective Cohort Study

Background: There is growing evidence for the need of therapeutic drug monitoring (TDM) of the active compound Mycophenolic Acid (MPA) of mycophenolate mofetil therapy for the management of antirejection therapy after pediatric renal transplantation. While there is substantial inter- and intra-patient variability of MPA exposure, the factors affecting its apparent clearance (CL/F) are understudied. The objective of this study was to determine the relationship between MPA CL/F, eGFR, creatinine, Cystatin C, triglycerides, cholesterol and albumin. Material and Methods: We calculated 1004 estimated mass-spectrometry-determined MPA CL/F using trough concentrations from 35 pediatric renal transplant patients. Results: Mean age was 8.7±4.6 years at transplant with a median follow-up of 5.8 years. Each patient had a median of 30 MPA trough concentrations. The median MPA AUC was 53.21 mg*h/L, the median CL/F was 8.66 L/h. Univariate and multivariate analysis revealed significant correlations of CL/F with creatinine, triglycerides, cholesterol and albumin, and very weakly with hemoglobin, whereas cystatin C was unrelated. Especially higher lipid levels and weekly, but significantly, lower albumin augmented CL/F. However, the correlations were not strong enough to predict CL/F. Conclusion: The data presented indicate the necessity for MPA TDM and suggest that dose modifications may apply in the face of low serum albumin and hyperlipidemia.

The impact of omeprazole on mycophenolate pharmacokinetics in kidney transplant recipients.

BackgroundThe absorption rates of mycophenolate mofetil (MMF) and enteric-coated mycophenolate sodium (EC-MPS) may be influenced by the concomitant use of omeprazole.MethodsOne hundred kidney transplant patients were recruited during their outpatient visits, including 50 on MMF and 50 on EC-MPS. At the clinic, a predose mycophenolic acid (MPA) sample (C0) was collected; subsequently, the participants received the proton-pump inhibitor omeprazole along with either MMF or EC-MPS. Two more blood samples were collected at 1.5 and 3.5 hours and used to estimate an area under the curve (AUC) from zero to 12 hours [AUC (0-12)].ResultsThe mean number of months after transplant was 92 months. The median AUC (0-12) and C0 results were 62.2 mg·h/L and 2.0 mg/L for the MMF group and 71.9 mg·h/L and 1.8 mg/L for the EC-MPS group (P = 0.160 and 0.225, respectively). Interestingly, 54% of the MMF group and 62% of the EC-MPS group showed AUCs above the target values. The correlation between MPA C0 and the predicted AUC was poor in both groups.ConclusionOmeprazole can be safely co-administered with either MMF or EC-MPS, as it did not compromise the MPA exposure. Unexpectedly, however, a high percentage of patients presented MPA AUCs exceeding the target value, highlighting the importance of periodically assessing MPA level.

Mycophenolate mofetil for systemic sclerosis: drug exposure exhibits considerable inter-individual variation\u2014a prospective, observational study

ObjectiveMycophenolate mofetil (MMF) is an established therapy for systemic sclerosis (SSc), but its pharmacokinetics in this disease remains unexplored. We have investigated drug exposure in MMF-treated patients with SSc in relation to clinical features of the disease and common concomitant drugs.MethodsThis study was predefined to include 35 MMF-treated SSc patients who were using MMF at a fixed dose of 0.5, 1.0 or 1.5 g twice daily since at least 3 months. The 12-h drug exposure of the active MMF metabolite mycophenolic acid (MPA) was estimated by repeated analysis of plasma MPA over a 6-h period. This 12-h drug exposure was dose normalised to a daily intake of 3 g MMF (MPA_AUC3g) in order to compare subjects using MMF at different doses. Drug exposure was analysed in reference to the clinical characteristics including body weight, renal function, autoantibodies, intestinal dysbiosis, intestinal inflammation assessed by faecal (F)-calprotectin, intestinal symptoms assessed by the University of California Los Angeles Scleroderma Trial Consortium Gastrointestinal Tract Instrument 2.0 and concomitant drug usage including proton-pump inhibitors (PPI).ResultsThirty-four out of 35 study participants completed the study. The mean daily MMF dose was 2.1 g. Drug exposure expressed as MPA_AUC3g varied up to 8-fold between patients (median 115, range 27–226 mg h/L).MPA_AUC3g was inversely related to body weight (rs = − 0.58, p < 0.001) and renal function (rs = − 0.34, p = 0.054). Anti-topoisomerase-1 antibodies and male sex were associated with lower MPA_AUC3g (87 vs 123 and 71 vs 141; p = 0.008 and p = 0.015, respectively). MPA_AUC3g was inversely related to the intestinal abundance of lactobacilli and to F-calprotectin (rs = − 0.54, p = 0.004; rs = − 0.36, p = 0.034), but not to gastrointestinal symptoms. MPA_AUC3g was inversely related to PPI usage (rs = − 0.45, p = 0.007). We found no association between MPA_AUC3g and disease subtype, disease duration or disease activity.ConclusionMMF-treated SSc patients exhibit considerable inter-individual variation in drug exposure, and lower MPA levels were primarily found in PPI users with poor prognostic factors. Body weight, renal function, sex, serology, gastrointestinal manifestations and/or measuring individual MPA exposure should be considered when using MMF for SSc.

Effect of the proton-pumpInhibitor pantoprazole on MycoPhenolic ACid exposure in kidney and liver transplant recipienTs (IMPACT study): a randomized trial.

Mycophenolic acid (MPA) is widely utilized as an immunosuppressant in kidney and liver transplantation, with reports suggesting an independent relationship between MPA concentrations and adverse allograft outcome. Proton-pump inhibitors (PPIs) may have variable effects on the absorption of different MPA formulations leading to differences in MPA exposure. A multicentre, randomized, prospective, double-blind placebo-controlled cross-over study was conducted to determine the effect of the PPI pantoprazole on the MPA and its metabolite MPA-glucuronide (MPA-G) area under the curve (AUC) >12 h (MPA-AUC12 h) in recipients maintained on mycophenolate mofetil (MMF) or enteric-coated mycophenolate sodium (EC-MPS). We planned a priori to examine separately recipients maintained on MMF and EC-MPS for each pharmacokinetic parameter. The trial (and protocol) was registered with the Australian New Zealand Clinical Trials Registry on 24 March 2011, with the registration number of ACTRN12611000316909 ('IMPACT' study). Of the 45 recipients screened, 40 (19 MMF and 21 EC-MPS) were randomized. The mean (standard deviation) recipient age was 58 (11) years with a median (interquartile range) time post-transplant of 43 (20-132) months. For recipients on MMF, there was a significant reduction in the MPA-AUC12 h [geometric mean (95% confidence interval) placebo: 53.9 (44.0-65.9) mg*h/L versus pantoprazole: 43.8 (35.6-53.4) mg*h/L; P = 0.004] when pantoprazole was co-administered compared with placebo. In contrast, co-administration with pantoprazole significantly increased MPA-AUC12 h [placebo: 36.1 (26.5-49.2)mg*h/L versus pantoprazole: 45.9 (35.5-59.3)mg*h/L; P = 0.023] in those receiving EC-MPS. Pantoprazole had no effect on the pharmacokinetic profiles of MPA-G for either group. The co-administration of pantoprazole substantially reduced the bioavailability of MPA in patients maintained on MMF and had the opposite effect in patients maintained on EC-MPS, and therefore, clinicians should be cognizant of this drug interaction when prescribing the different MPA formulations.

Inosine 5'-Monophosphate Dehydrogenase Activity for the Longitudinal Monitoring of Mycophenolic Acid Treatment in Kidney Allograft Recipients.

Mycophenolic acid (MPA) is a standard immunosuppressant in organ transplantation. A simple monitoring biomarker for MPA treatment has not been established so far. Here, we describe inosine 5'-monophosphate dehydrogenase (IMPDH) monitoring in erythrocytes and its application to kidney allograft recipients. IMPDH activity measurements were performed using a high-performance liquid chromatography assay. Based on 4203 IMPDH measurements from 1021 patients, we retrospectively explored the dynamics early after treatment start. In addition, we analyzed the influence of clinically relevant variables on IMPDH activity in a multivariate model using data from 711 stable patients. Associations between IMPDH activity and clinical events were evaluated in hospitalized patients. We found that IMPDH activity reflects MPA exposure after 8 weeks of constant dosing. In addition to dosage, body mass index, renal function, and coimmunosuppression affected IMPDH activity. Significantly lower IMPDH activities were found in patients with biopsy-proven acute rejection as compared to patients without rejection (median [interquartile range]: 696 [358-1484] versus 1265 [867-1618] pmol xanthosine-5'-monophosphate/h/mg hemoglobin, P < 0.001). The highest IMPDH activities were observed in hospitalized patients with clinically evident MPA toxicity as compared to patients with hospitalization not related to MPA treatment (1548 [1021-2270] versus 1072 [707-1439] pmol xanthosine-5'-monophosphate/h/mg hemoglobin; P < 0.001). Receiver operating characteristic curve analyses underlined the usefulness of IMPDH to predict rejection episodes (area, 0.662; confidence interval, 0.584-0.740; P < 0.001) and MPA-associated adverse events (area, 0.632; confidence interval, 0.581-0.683; P < 0.001), respectively. IMPDH measurement in erythrocytes is a novel and useful strategy for the longitudinal monitoring of MPA treatment.

A new model to determine Optimal Exposure to Tacrolimus and Mycophenolate Mofetil after renal transplantation.

Drug dosing for Tacrolimus (TAC) and Mycophenolate Mofetil (MMF) after kidney transplantation remains challenging. Therapeutic drug monitoring (TDM) offers a means to individualize drug dosing and improve outcomes. In this observational study, patients having mycophenolic acid (MPA) exposure assessed by limited sampling strategy (LSS) within the first 6months were included and followed for 1year. A total of 113 clinical events occurring in 110 patients were classified into 3 groups: Group 1 Stable (n=34), Group 2 Over drug exposed (n=64) having infections or drug toxicity and Group 3 Under drug exposed (n=15) developing rejection or de novo donor-specific alloantibodies. Although TAC levels, MMF dose, MPA, and MPA Glucuronide (MPAG) exposure, expressed as area under curve (AUC), individually failed to predict outcomes, a scoring model incorporating all 3 drug levels TAC TDM×(MPA AUC+MPAG/10 AUC) correctly classified outcomes. A score over 1071 had a sensitivity and specificity of 0.94 (95% CI 0.56-0.83) and 0.84 (95% CI 0.69-0.89) for over exposure. A score below 625 had a sensitivity and specificity of 0.76 (95% CI 0.53-0.93) and 0.80 (95% CI 0.41-0.70) for under exposure. This integrated model of assessing TAC and MMF exposure may facilitate individualized therapy.

Effect of Protein Binding on Exposure of Unbound and Total Mycophenolic Acid: A Population Pharmacokinetic Analysis in Chinese Adult Kidney Transplant Recipients.

ObjectivesThe population pharmacokinetic (popPK) characteristics of total mycophenolic acid (tMPA) have been investigated in various ethnic populations. However, investigations of popPK of unbound MPA (uMPA) are few. Thus, a popPK analysis was performed to: (1) characterize the PK of uMPA and tMPA and its 7-O-mycophenolic acid glucuronide (MPAG) metabolite in kidney transplant patients cotreated with cyclosporine (CsA), and (2) identify the clinically significant covariates that explain variability in the dose–exposure relationship.MethodsA total of 740 uMPA, 741 tMPA, and 734 total MPAG (tMPAG) concentration–time data from 58 Chinese kidney transplant patients receiving MPA in combination with CsA were analyzed using NONMEM® software with the stochastic approximation expectation maximization (SAEM) followed by the important sampling (IMP) method. The influence of covariates was tested using a stepwise procedure.ResultsThe PK of uMPA and unbound MPAG (uMPAG) were characterized by a two- and one-compartment model with first-order elimination, respectively. A linear protein binding model was used to link uMPA and tMPA. Apparent clearance (CL/F) and central volume of distribution (VC/F) of uMPA (CLuMPA/F and VCuMPA/F, respectively) and protein binding rate constant (kB) were estimated to be 851 L/h [relative standard error (RSE), 7.1%], 718 L (18.5%) and 53.4/h (2.3%), respectively. For uMPAG, the population values (RSE) of CL/F (CLuMPAG) and VC/F (VCuMPAG/F) were 5.71 L/h (4.4%) and 29.9 L (7.7%), respectively. Between-subject variability (BSVs) on CLuMPA/F, VCuMPA/F, CLuMPAG/F, and VCuMPAG/F were 51.0, 80.0, 31.8 and 48.4%, respectively, whereas residual unexplained variability (RUVs) for uMPA, tMPA, and uMPAG were 47.0, 45.9, and 22.0%, respectively. Significant relationships were found between kB and serum albumin (ALB) and between CLuMPAG/F and glomerular filtration rate (GFR). Additionally, model-based simulation showed that changes in ALB concentrations substantially affected tMPA but not uMPA exposure.ConclusionsThe established model adequately described the popPK characteristics of the uMPA, tMPA, and MPAG. The estimated CLuMPA/F and unbound fraction of MPA (FUMPA) in Chinese kidney transplant recipients cotreated with CsA were comparable to those published previously in Caucasians. We recommend monitoring uMPA instead of tMPA to optimize mycophenolate mofetil (MMF) dosing for patients with lower ALB levels.

Pregnancy outcomes in heart transplant recipients

The population of female heart transplant recipients of reproductive age is growing, and counseling regarding reproductive decisions is important. We describe maternal and fetal outcomes of pregnancy in the Transplant Pregnancy Registry International. Data regarding pregnancies between 1987 and 2016 were collected via questionnaires, phone interviews, and medical records review. Demographics, comorbidities, changes in immunosuppressive regimens, rejection episodes during pregnancy, data on maternal retransplants, and deaths were recorded. A total of 91 patients reported 157 pregnancies. Mean maternal age at conception was 27 ± 5.6 years. The most common indications for transplant were congenital heart disease (22%) and viral myocarditis (18%). Average transplant to conception interval was 7 ± 6.1 years. Immunosuppression was calcineurin inhibitor-based in almost all patients, with 20% of recipients taking mycophenolic acid (MPA) while pregnant. Complications during pregnancy included pre-eclampsia (23%) and infections (14%). Rejection was reported during 9% of pregnancies and within 3 months postpartum in 7%. Livebirths occurred in 69%, with no neonatal deaths. Miscarriages occurred in 26% of pregnancies, 49% of which had MPA exposure. Mean follow-up post pregnancy was 8.9 ± 6.5 years. At last follow-up, 30 recipients had died, an average of 9.4 ± 6.2 years after pregnancy. The most common causes included allograft vasculopathy and rejection. This is the largest reported series of pregnancies in heart transplant recipients and demonstrates that two thirds of pregnancies reported are successful. MPA exposure is associated with increased risk of teratogenicity and miscarriage. Pre-pregnancy counseling should include discussions of risk of MPA exposure, rejection, graft dysfunction, and maternal survival.

Mycophenolic acid pharmacogenomics in kidney transplantation

Mycophenolic acid (MPA) is a potent antiproliferative drug prescribed to prevent acute rejection in kidney transplantation. MPA reversibly inhibits the enzymes involved in the synthesis of guanosine nucleotides, thus preventing DNA replication of immune cells. Consequently, the repression of both cell and humoral immunity induces renal allograft tolerance. MPA is an effective and safe immunosuppressive drug, but some patients show variability in drug concentration, acute rejection, graft dysfunction, or MPA-related adverse events. Although the pharmacogenomics of immunosuppressive drugs has been widely investigated, MPA has been explored to a lesser extent. This review of MPA pharmacogenomic studies, included pharmacokinetics, adverse events, and main clinical outcomes of MPA treatment in kidney transplantation. Associations of variants in genes encoding MPA metabolizing enzymes, transporters, and targets with drug efficacy and safety are described. Most pharmacogenetic studies have focused on small sample sizes and few simultaneously analyzed genetic variants. Some studies reported significant associations of pharmacokinetics- and pharmacodynamics-related genes with MPA exposure, acute rejection, graft dysfunction, hematological events, and gastrointestinal complications. However, even large cohorts did not replicate the findings, possibly due to divergent study design, immunosuppressive scheme, follow-up time, and other factors. Finally, the heterogeneity of aspects between studies limit conclusions on pharmacogenetic biomarkers of MPA in kidney transplantation.

A Limited Sampling Strategy for Therapeutic Drug Monitoring of Mycophenolate Mofetil for Prophylaxis of Acute Graft-Versus-Host Disease in Allogeneic Stem Cell Transplantation

A universally accepted strategy for therapeutic drug monitoring (TDM) of mycophenolate mofetil (MMF) in the prevention of acute graft-versus-host disease (aGVHD) in allogenic hematopoietic stem cell transplantation (alloHSCT) does not exist. We explored the feasibility of developing a limited sampling strategy (LSS) for TDM of MMF in this setting. Patients undergoing alloHSCT received standard MMF-cyclosporine prophylaxis, with MMF administered twice daily (BD) for matched transplant recipients or thrice daily (TID) in haploidentical transplantation. Intensive blood sampling was carried out on day 7 and area under the concentration–time curve (AUC) of mycophenolic acid (MPA), the active metabolite, was estimated using noncompartmental analysis. The ability of MPA exposure defined by AUC0-12 to discriminate between responders (patients who did not develop GVHD) and nonresponders (patients who developed GVHD) was determined by receiver operating characteristic curve analysis. Patients were divided into training and validation sets within BD and TID groups. Mathematical equations were developed from the training set to predict AUC0-12 from an abbreviated AUC involving a limited number of sampling points. The equations were validated in the validation set by comparing the MPA AUC0-12 predicted from LSS with the observed AUC0-12. It was observed that patients with AUC0-12 ≤18.99 mg*h/L had a higher risk of developing aGVHD [odds ratio (OR) = 2.63 (1.17 to 5.87), P = 0.06]. The benefit was more in matched transplant recipients [OR = 3.5 (1.30 to 9.49), P = 0.05] as compared to haploindentical transplant [OR = 2.8 (0.49 to 15.91), P = NS]. Using the mathematical equations, the observed AUC0-12 was predicted with 92.31% accuracy in the BD subset and 100% accuracy in the TID subset for a combined accuracy of 94.76%. A set of just three samples that constituted the abbreviated AUC1-4 was used to develop the predictive models. The LSS could be employed for the therapeutic monitoring of MMF particularly in patients undergoing matched hematopoietic stem cell transplantation.

Generation and Validation of a Limited Sampling Strategy to Monitor Mycophenolic Acid Exposure in Children With Nephrotic Syndrome.

Mycophenolate mofetil (MMF) plays an increasingly important role in the treatment of children with nephrotic syndrome, especially in steroid sparing protocols. Recent publications show the relationship of exposure to its active moiety mycophenolic acid (MPA) and clinical efficacy. Performance of full-time pharmacokinetic (PK) profiles, however, is inconvenient and laborious. Established limited sampling strategies (LSS) to estimate the area under the concentration (AUC) versus time curve of MPA (MPA-AUC) in pediatric renal transplant recipients cannot be easily transferred to children suffering from nephrotic syndrome, mainly because of the lack of concomitant immunosuppressive therapy. We therefore aimed for the generation and validation of a LSS to estimate MPA exposure to facilitate therapeutic drug monitoring in children with nephrotic syndrome. We performed 27 complete PK profiles in 23 children in remission [mean age (±SD):12.3 ± 4.26 years] to generate and validate an LSS. Sampling time points were before administration (C0) and 0.5, 1, 1.5, 2, 4, 6, 8, and 12 hours after the administration of MMF. MPA was measured by enzyme multiplied immunoassay technique. There was no concomitant treatment with calcineurin inhibitors. Mean daily dose of MMF was 927 ± 209 mg/m of body surface area resulting in a mean MPA-AUC0-12 value of 59.2 ± 29.3 mg × h/L and a predose level of 3.03 ± 2.24 mg/L. Between-patient variability of dose-normalized MPA-AUC0-12 was high (coefficient of variation: 45.5%). Correlation of predose levels with the corresponding MPA-AUC0-12 was moderate (r = 0.59) in a subgroup of 18 patients (20 PK profiles, generation group). An algorithm based on 3 PK sampling time points during the first 2 hours after MMF dosing (estimated AUC0-12 = 8.7 + 4.63 × C0 + 1.90 × C1 + 1.52 × C2) was able to predict MPA-AUC with a low percentage prediction error (3.88%) and a good correlation of determination (r = 0.90). Validation of this algorithm in a randomized separate group of 6 patients (7 PK profiles, validation group) resulted in comparably good correlation (r = 0.95) and low percentage prediction error (5.57%). An abbreviated profile within the first 2 hours after MMF dosing gives a good estimate of MPA exposure in children with nephrotic syndrome and hence has the potential to optimize MMF therapy.

A structural determinant of mycophenolic acid resistance in eukaryotic inosine 5'-monophosphate dehydrogenases.

Mycophenolic acid (MPA) is a potent natural product inhibitor of fungal and other eukaryotic inosine 5'-monophosphate dehydrogenases (IMPDHs) originally isolated from spoiled corn silage. MPA is produced by the filamentous fungi Penicillium brevicompactum, which contains two IMPDHs, PbIMPDHA and PbIMPDHB, both of which are MPA-resistant. The MPA binding sites of these enzymes are identical to MPA-sensitive IMPDHs, so the structural determinants of resistance are unknown. Here we show that a single residue, Ser267, accounts for the MPA resistance of PbIMPDHA. Substitution of Ser267 with Ala, the residue most commonly found in this position in eukaryotic IMPDHs, makes PbIMPDHA sensitive to MPA. Conversely, Aspergillus nidulans IMPDH becomes MPA-resistant when the analogous Ala residue is substituted with Ser. These substitutions have little effect on the catalytic cycles of either enzyme, suggesting the fitness costs are negligible despite the strong conservation of Ala at this position. Intriguingly, while only 1% of fungal IMPDHs contain Ser or Thr at position 267, these residues are found in the IMPDHs from several Aspergillus species that grow at the low temperatures also favored by Penicillium. Perhaps Ser/Thr267 is an evolutionary signature of MPA exposure.

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

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

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.

Exposure-Toxicity Relationships of Mycophenolic Acid in Adult Kidney Transplant Patients.

Mycophenolic acid is commonly prescribed in adult kidney transplant recipients for preventing graft rejection. A therapeutic target for total mycophenolic acid area under the concentration-time curve (30-60mgh/L) has been established in adult kidney transplant recipients and widely referenced today. However, this specific target range does not adequately characterize mycophenolic acid-associated adverse effects. The primary objective of this qualitative and critical review was to characterize the exposure-toxicity relationships of mycophenolic acid in an attempt to determine whether exposure thresholds can be identified. The secondary objective was to determine the associations of clinical variables with specific adverse effects. The inclusion criteria consisted of all peer-reviewed papers in adult kidney transplant subjects (average study age > 18years) with both exposure (area under the concentration-time curve) and toxicity data. The exclusion criteria were papers involving the pediatric population, studies lacking either area under the concentration-time curve or toxicity data, or studies with no apparent reported variations in area under the concentration-time curves. Of the 28 papers identified, inconsistent findings have been reported for the most frequently characterized adverse events of mycophenolic acid (gastrointestinal, infectious, and hematological), while promising exposure thresholds (i.e., > 40-60mgh/L for total mycophenolic acid) have been suggested by a few studies. The roles of free mycophenolic acid exposure, mycophenolic acid metabolites, or clinical factors influencing the manifestation of the toxicities also remain to be clarified. Although it is not yet possible to define toxicity threshold(s) for the purpose of mycophenolic acid therapeutic drug monitoring, the information obtained and the limitations identified in this comprehensive literature body have provided a good foundation for future investigations.

Pharmacokinetics of Enteric-Coated Mycophenolate Sodium in Lupus Nephritis (POEMSLUN).

Background:Mycophenolate mofetil or enteric-coated mycophenolate sodium (EC-MPS) and steroids are used for induction and maintenance therapy in severe lupus nephritis. Blood concentrations of mycophenolic acid (MPA), the active metabolite of these drugs, vary among patients with lupus nephritis. The objective of this study was to examine whether concentration-controlled (CC) dosing (through therapeutic drug monitoring) of EC-MPS results in a higher proportion of participants achieving target exposure of MPA compared with fixed-dosing (FD). An additional aim of the study was to evaluate the influence of CC dosing on clinical outcomes.Methods:Nineteen participants were randomly assigned either to the FD or CC group. All the participants were eligible to have free and total measurements of MPA over a period of 8–12 hours on 3 different occasions. Area under the concentration–time curve between 0 and 12 hours (AUC0-12) was calculated using noncompartmental methods. Dose of EC-MPS was titrated according to AUC0-12 in the CC group.Results:Thirty-two AUC0-12 measurements were obtained from 9 FD and 9 CC participants. Large inter-patient variability was observed in both groups but was more pronounced in the FD group. There were no significant differences between FD and CC participants in any pharmacokinetic parameters across the study visits, except for total C0 (FD 2.0 ± 0.3 mg/L versus CC 1.1 ± 0.3; P = 0.01) and dose-normalized C0 (FD 2.9 ± 0.2 mg/L/g versus CC 2.1 ± 0.7 mg/L/g; P = 0.04) at the second visit and total AUC0-12 (FD 66.6 ± 6.0 mg·h/L versus CC 35.2 ± 11.4 mg·h/L; P = 0.03) at the third visit. At the first study visit, 33.3% of the FD and 11.1% of the CC participants achieved the target area under the concentration–time curve (P = 0.58). From the second visit, none of the FD participants, compared with all the CC participants, achieved target AUC0-12 (P = 0.01). More CC participants achieved remission compared with FD participants (absolute difference of −22.2, 95% confidence interval 0.19 to 0.55; P = 0.62). The mean free MPA AUC0-12 was significantly lower in those who had complete remission.Conclusions:CC participants reached target AUC0-12 quicker. Larger studies are required to test clinical efficacy.

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

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