Explaining variability in mycophenolic acid exposure to optimize mycophenolate mofetil dosing: a population pharmacokinetic meta-analysis of mycophenolic acid in renal transplant recipients

Model-informed precision dosing: State of the art and future perspectives

Model-informed precision dosing (MIPD) stands as a significant development in personalized medicine to tailor drug dosing to individual patient characteristics. MIPD moves beyond traditional therapeutic drug monitoring (TDM) by integrating mathematical predictions of dosing, and considering patient-specific factors (patient characteristics, drug measurements) as well as different sources of variability. For this purpose, rigorous model qualification is required for the application of MIPD in patients. This review delves into new methods in model selection and validation, also highlighting the role of machine learning in improving MIPD, the utilization of biosensors for real-time monitoring, as well as the potential of models integrating biomarkers for efficacy or toxicity for precision dosing. The clinical evidence of TDM and MIPD is discussed for various medical fields including infection medicine, oncology, transplant medicine, and inflammatory bowel diseases, thereby underscoring the role of pharmacokinetics/pharmacodynamics and specific biomarkers. Further research, particularly randomized clinical trials, is warranted to corroborate the value of MIPD in enhancing patient outcomes and advancing personalized medicine.

Influence of UDP-Glucuronosyltransferase Polymorphisms on Mycophenolic Acid Metabolism in Renal Transplant Patients

This study aimed to evaluate the effects of UDP-glucuronosyltransferase (UGT) polymorphisms on mycophenolic acid (MPA) metabolism in renal transplant patients. A total of 11 single nucleotide polymorphisms (SNPs) of UGT1A1, UGT1A7, UGT1A8, UGT1A9, UGT1A10, and UGT2B7 were genotyped in 79 renal transplant patients. The associations of SNPs and clinical factors with dose-adjusted MPA area under the plasma concentration-time curve (AUC/D), the dose-adjusted plasma concentration (C0/D) of 7-O-MPA-glucuronide (MPAG), and the dose-adjusted plasma concentration (C0/D) of acyl MPAG (AcMPAG) were analyzed. In the univariate analysis, UGT1A1 rs4148323, age, and anion gap were associated with MPA AUC/D. MPA AUC/D was higher in patients with the GA genotype of UGT1A1 rs4148323 compared to patients with the GG genotype. UGT1A1 rs4148323, UGT1A9 rs2741049 and clinical factors, including age, serum total bilirubin, adenosine deaminase, anion gap, urea, and creatinine, were associated with MPAG C0/D. UGT2B7 rs7438135, UGT2B7 rs7439366, and UGT2B7 rs7662029 also were associated with AcMPAG C0/D. Multiple linear regression analysis showed that UGT1A9 rs2741049 and indirect bilirubin were negatively correlated with MPAG C0/D (P = .001; P = .039), and UGT2B7 rs7662029 was positively correlated with AcMPAG C0/D (P = .008). This study demonstrates a significant influence of UGT1A9 rs2741049 and UGT2B7 rs7662029 polymorphisms on the metabolism of MPA in vivo.

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.

Dynamic Monitoring of Intracellular Tacrolimus and Mycophenolic Acid Therapy in Renal Transplant Recipients Using Magnetic Bead Extraction Combined with LC-MS/MS

BACKGROUND

Tacrolimus (TAC) and mycophenolic acid (MPA) are commonly used immunosuppressive therapies after renal transplant. Our objective was to quantify TAC and MPA concentrations in peripheral blood mononuclear cells (PBMCs) using liquid chromatography tandem mass spectrometry (LC-MS/MS) and to evaluate and validate the performance of the methodology. A prospective follow-up cohort study was conducted to determine whether intracellular concentrations were associated with adverse outcomes in renal transplants.

METHODS

PBMCs were prepared using the Ficoll separation technique and purified with erythrocyte lysis. The cells were counted using Sysmex XN-3100 and then packaged and frozen according to a 50 µL volume containing 1.0 × 106 cells. TAC and MPA were extracted using MagnaBeads and quantified using an LC-MS/MS platform. The chromatography was run on a reversed-phase Waters Acquity UPLC BEH C18 column (1.7 µm, 50 mm × 2.1 mm) for gradient elution separation with a total run time of 4.5 min and a flow rate of 0.3 mL/min. Mobile phases A and B were water and methanol, respectively, each containing 2 mM ammonium acetate and 0.1% formic acid. Renal transplant recipients receiving TAC and MPA in combination were selected for clinical validation and divided into two groups: a stable group and an adverse outcome group. The concentrations were dynamically monitored at 5, 7, 14, and 21 days (D5, D7, D14, and D21) and 1, 2, 3, and 6 months (M1, M2, M3, and M6) after operation.

RESULTS

Method performance validation was performed according to Food and Drug Administration guidelines, showing high specificity and sensitivity. The TAC and MPA calibration curves were linear (r2 = 0.9988 and r2 = 0.9990, respectively). Both intra-day and inter-day imprecision and inaccuracy were less than 15%. Matrix effects and recoveries were satisfactory. The TAC and MPA concentrations in 304 "real" PBMC samples from 47 renal transplant recipients were within the calibration curve range (0.12 to 16.40 ng/mL and 0.20 to 4.72 ng/mL, respectively). There was a weak correlation between PBMC-C0TAC and WB-C0TAC (p < 0.05), but no correlation was found for MPA. The level of immunosuppressive intra-patient variation (IPV) was higher in PBMC at 77.47% (55.06, 97.76%) than in WB at 34.61% (21.90, 49.85%). During the dynamic change in C0TAC, PBMC-C0TAC was in a fluctuating state, and no stable period was found. PBMC-C0TAC did not show a significant difference between the stable and adverse outcome group, but the level of the adverse outcome group was generally higher than that of the stable group.

CONCLUSIONS

Compared with conventional therapeutic drug monitoring, the proposed rapid and sensitive method can provide more clinically reliable information on drug concentration at an active site, which has the potential to be applied to the clinical monitoring of intracellular immunosuppressive concentration in organ transplantation. However, the application of PBMC-C0TAC in adverse outcomes of renal transplant should be studied further.

Clinical Evidence on the Purported Pharmacokinetic Interactions between Corticosteroids and Mycophenolic Acid

Corticosteroids (steroids) are commonly used concurrently with mycophenolic acid (MPA) as the first-line immunosuppression therapy for the prevention of rejection in solid organ transplantations. Steroids are also commonly administered with MPA in various autoimmune disorders such as systemic lupus erythematosus and idiopathic nephrotic syndrome. Despite various review articles having suggested the presence of pharmacokinetic interactions between MPA and steroids, definitive data have not yet been demonstrated. The aim of this Current Opinion is to critically evaluate the available clinical data and propose the optimal study design for characterising the MPA-steroid pharmacokinetic interactions. The PubMed and Embase databases were searched for relevant clinical articles in English as of September 29, 2022, where a total of 8 papers have been identified as supporting and 22 as non-supporting the purported drug interaction. To objectively evaluate the data, novel assessment criteria to effectively diagnose the interaction based on known MPA pharmacology were formulated, including the availability of independent control groups, prednisolone concentrations, MPA metabolite data, unbound MPA concentrations, and the characterisations of entero-hepatic recirculation and MPA renal clearance. Overall, the majority of the identified corticosteroid data were pertaining to prednisone or prednisolone. Our assessment indicated that no conclusive mechanistic data supporting the interaction are available in the current clinical literature, and further studies are required to quantify the effects/mechanisms of steroid-tapering or withdrawal on MPA pharmacokinetics. This current opinion provides justification for further translational investigations, as this particular drug interaction has the potential to exert significant adverse outcomes in patients prescribed MPA.

Recommendations for living donor kidney transplantation

This Guide for Living Donor Kidney Transplantation (LDKT) has been prepared with the sponsorship of the Spanish Society of Nephrology (SEN), the Spanish Transplant Society (SET), and the Spanish National Transplant Organization (ONT). It updates evidence to offer the best chronic renal failure treatment when a potential living donor is available. The core aim of this Guide is to supply clinicians who evaluate living donors and transplant recipients with the best decision-making tools, to optimise their outcomes. Moreover, the role of living donors in the current KT context should recover the level of importance it had until recently. To this end the new forms of incompatible HLA and/or ABO donation, as well as the paired donation which is possible in several hospitals with experience in LDKT, offer additional ways to treat renal patients with an incompatible donor. Good results in terms of patient and graft survival have expanded the range of circumstances under which living renal donors are accepted. Older donors are now accepted, as are others with factors that affect the decision, such as a borderline clinical history or alterations, which when evaluated may lead to an additional number of transplantations. This Guide does not forget that LDKT may lead to risk for the donor. Pre-donation evaluation has to centre on the problems which may arise over the short or long-term, and these have to be described to the potential donor so that they are able take them into account. Experience over recent years has led to progress in risk analysis, to protect donors' health. This aspect always has to be taken into account by LDKT programmes when evaluating potential donors. Finally, this Guide has been designed to aid decision-making, with recommendations and suggestions when uncertainties arise in pre-donation studies. Its overarching aim is to ensure that informed consent is based on high quality studies and information supplied to donors and recipients, offering the strongest possible guarantees.

Utility of salivary mycophenolic acid concentration monitoring: Modeling and Monte Carlo validation approach

The results of the previous studies demonstrated an association between mycophenolic acid (MPA) exposure, serum albumin level (ALB), and adverse effects in kidney transplant patients. The aim was the identification of mathematical correlation and association between both, total and unbound MPA concentration in relation to ALB, body mass (BM), age and estimated glomerular filtration rate (eGFR) in stable kidney transplant recipients. Furthermore, investigation was conducted with the aim to clarify the role of salivary concentration (CSAL ) of MPA in adverse effect profile. In order to analyze the association between total and salivary concentration of MPA in relation to ALB, BM, age and eGFR, a least squares method for determining the correlation between these parameters was performed. In addition, derived mathematical model based on experimental data can also be performed and simulated through the Monte Carlo (MC) approach. Adverse effects were grouped according to the nature of symptoms and scored by a previously published validated system. Numerically calculated values of CSAL from the models [CSAL  = f(ALB, BM, age, eGFR, CP ) = a00  + a10 *(ALB, BM, age, eGFR) + a01 *CP ] were then compared with those from validation set of patients, where the best fitting model was for ALB [CSAL  = 54.96-1.64*ALB +13.4*CP ]. Adverse effects estimation showed the difference in esthetic score, positively correlated with CSAL in the lower ALB group (145.41 ± 219.02 vs. 354.08 ± 262.19; with statistical significance p = .014) and almost significant for gastrointestinal score (167.69 ± 174.79 vs. 347.55 ± 320.95; p = .247). The study showed that CSAL MPA may contribute to management of adverse effects, but these findings require confirmation of clinical utility.

The combination of exposure to Tacrolimus, mycophenolic acid, Inosine 5'-Monophosphate Dehydrogenase activity and inhibition in the first week define early histological outcomes in renal transplant recipients

Therapeutic drug monitoring is routine for Tacrolimus, while levels are not routinely monitored for mycophenolic acid (MPA). This study investigated the effect of early post-transplant pharmacokinetics (PK) of MPA and Tacrolimus along with the pharmacodynamics (PD) of MPA on biopsy-proven acute rejection (BPAR) after renal transplantation. A prospective PK/PD study with limited sampling (three blood samples) was conducted in renal transplant recipients on week 1, around Day 6 (n = 42) and at the 3rd-month biopsy on Day 90 (n = 23). The partial exposures (area under curve [AUC]_0-3.5 h ) of both MPA and Tacrolimus obtained during the first week were more predictive of rejection (combined clinical and subclinical rejection) by Day 90 than their trough concentrations or Day 90 exposures. Patients with rejection had significantly worse renal function (eGFR) and a comparatively lower exposure to MPA during the first post-transplant week. The lower MPA exposure was also associated with sub-optimal inosine monophosphate dehydrogenase (IMPDH) inhibition in patients with rejection, and the probability of rejection was higher in the presence of an increased pre-transplant IMPDH activity. A composite of parameters, including MPA exposure and IMPDH activity was found to predict acute rejection and may be beneficial along with tacrolimus monitoring early after renal transplantation.

Pharmacokinetics and pharmacodynamics profiles of enteric-coated mycophenolate sodium in female patients with difficult-to-treat lupus nephritis

Relapsed or resistant lupus nephritis (LN) is considered a difficult-to-treat type of LN, and enteric-coated mycophenolate sodium (EC-MPS) has been used in this condition. Therapeutic drug monitoring using the area under the plasma mycophenolic acid concentration from 0 to 12 h postdose (MPA-AUC_0-12h ) ≥45 μg.h/ml is a useful approach to achieve the highest efficiency. This study assessed EC-MPS's pharmacokinetic (PK) and pharmacodynamic (PD) profiles and investigated an optimal level of the single time point of plasma MPA concentration. Nineteen biopsy-proven patients with class III/IV LN received 1440 mg/day of EC-MPS for 24 weeks. PK (maximum plasma MPA concentration [C_max ], time to C_max , and MPA-AUC_0-12h ) and PD (activity of inosine-5'-monophosphate dehydrogenase [IMPDH]) parameters were measured at weeks 2, 8, 16, and 24. We found that IMPDH activity decreased from baseline by 31-42% within 2-4 h after dosing, coinciding with the increased plasma MPA concentration. MPA-AUC_0-12h ≥45 μg.h/ml was best predicted by a single time point MPA concentration at C0.5, C2, C3, C4, and C8 (r²  = 0.516, 0.514, 0.540, 0.611, and 0.719, respectively), independent of dose, albumin, urine protein/creatinine ratio, and urinalysis. The MPA-C0.5 cutoff of 2.03 g/ml yielded the highest overall sensitivity of 85% and specificity of 88.2% in predicting MPA-AUC_0-12h ≥45 μg.h/ml. A single timepoint of plasma MPA-C0.5 ≥2.03 μg/ml may help guide EC-MPS adjustment to achieve adequate drug exposure. Further study of EC-MPS used to validate this cutoff is warranted.

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.

Heart Transplant in Older Adults

Purpose of Review

Older adults with end-stage heart failure may be candidates for heart transplantation (HT) and changing guidelines and institutional policies have increased the availability of HT for septuagenarians. This review explores historical, pre-HT evaluation, and post-HT outcomes for older adult HT recipients.

Recent Findings

Rates of HT in older adults have increased in the past decade and more than 800 septuagenarians have undergone HT. Older adult HT recipients have similar survival, rehospitalization, and graft failure rates when compared to younger patients despite additional comorbidities and higher risk donors.

Summary

HT is feasible in carefully selected older adults. As the number of older adults who are considered for HT increases, additional research into population-specific assessment tools will be needed. Furthermore, age-related immune changes warrant population-specific studies on immunosuppressive regimens.

Recent lessons learned from population pharmacokinetic studies of mycophenolic acid: physiological, genomic, and drug interactions leading to the prediction of drug effects

INTRODUCTION

Mycophenolic acid (MPA) is a widely used immunosuppressant in transplantation and autoimmune disease. Highly variable pharmacokinetics have been observed with MPA, but the exact mechanisms remain largely unknown.

AREAS COVERED

The current review provided a critical, comprehensive update of recently published population pharmacokinetic/dynamic models of MPA (n=16 papers identified from PubMed and Embase, inclusive from January 2017 to August 2021), with specific emphases on the intrinsic and extrinsic factors influencing the pharmacology of MPA. The significance of the identified covariates, potential mechanisms, and comparisons to historical literature have been provided.

EXPERT OPINION

While select covariates affecting the population pharmacokinetics of MPA are consistently observed and mechanistically supported, some variables have not been regularly reported and/or lacked mechanistic explanation. Very few pharmacodynamic models were available, pointing to the need to extrapolate pharmacokinetic findings. Ideal models of MPA should consist of: i) utilizing optimal sampling points to allow the characterizations of absorption, re-absorption, and elimination phases; ii) characterizing unbound/total MPA, MPA metabolites, plasma/urinary concentrations, and genetic polymorphisms to facilitate mechanistic interpretations; and iii) incorporating actual outcomes and pharmacodynamic data to establish clinical relevance. We anticipate the field will continue to expand in the next 5 to 10 years.

Transplant Prognosis in Kidney Transplant Recipients with Diabetes under Mycophenolic Acid-Focused Therapeutic Drug Monitoring

Mycophenolate mofetil is a key immunosuppressant that is metabolized into mycophenolic acid (MPA). The prognostic impact of MPA-focused therapeutic drug monitoring on allograft prognosis has not been determined in kidney transplant recipients with diabetes. In this study, we assessed the pharmacokinetics of MPA and allograft prognosis in recipients with diabetes. This study retrospectively analyzed 64 adult kidney transplant recipients. MPA blood concentration data (e.g., the time to the maximum concentration (Tmax), and the area under the concentration–time curve from 0 to 12 h (AUC_0–12)) were collected at 3 weeks and 3 months after kidney transplantation. Of the 64 recipients, 15 had pre-existing diabetes. At 3 months after kidney transplantation, the Tmax of MPA was significantly longer in recipients with diabetes (mean (standard deviation): 2.8 (2.1) h) than in recipients without diabetes (1.9 (1.1) h, p = 0.02). However, the allograft estimated glomerular filtration rate and acute rejection rate, including borderline change, did not differ according to the diabetes status in patients with adjusted AUC_0–12 of MPA within the target range. In conclusion, a longer Tmax of MPA was observed in recipients with diabetes; however, acceptable allograft prognosis was observed in kidney transplant recipients with diabetes and a sufficient AUC_0–12 of MPA.

Model-informed precision dosing to optimise immunosuppressive therapy in renal transplantation

Immunosuppressive therapy is pivotal for sustained allograft and patient survival after renal transplantation. However, optimally balanced immunosuppressive therapy is challenged by between-patient and within-patient pharmacokinetic (PK) variability. This could warrant the application of personalised dosing strategies to optimise individual patient outcomes. Pharmacometrics, the science that investigates the xenobiotic-biotic interplay using computer-aided mathematical modelling, provides options to describe and quantify this PK variability and enables identification of patient characteristics affecting immunosuppressant PK and treatment outcomes. Here, we review and critically appraise the available pharmacometric model-informed dosing solutions for the typical immunosuppressants in modern renal transplantation, to guide their initial and subsequent dosing.

Immunosuppression Considerations for Older Kidney Transplant Recipients

PURPOSE OF REVIEW

While kidney transplantation improves the long-term survival of the majority of patients with end-stage kidney disease (ESKD), age-related immune dysfunction and associated comorbidities make older transplant recipients more susceptible to complications related to immunosuppression. In this review, we discuss appropriate management of immunosuppressive agents in older adults to minimize adverse events, avoid acute rejection, and maximize patient and graft survival.

RECENT FINDINGS

Physiological changes associated with senescence can impact drug metabolism and increase the risk of posttransplant infection and malignancy. Clinical trials assessing the safety and efficacy of immunosuppressive agents in older adults are lacking. Recent findings from U.S. transplant registry-based studies suggest that risk-adjusted death-censored graft failure is higher among older patients who received antimetabolite avoidance, mammalian target of rapamycin inhibitor (mTORi)-based, and cyclosporine-based regimens. Observational data suggest that risk-adjusted mortality may be increased in older patients who receive mTORi-based and cyclosporine-based regimens but lower in those managed with T-cell induction and maintenance steroid avoidance/withdrawal.

SUMMARY

Tailored immunosuppression management to improve patient and graft survival in older transplant recipients is an important goal of personalized medicine. Lower intensity immunosuppression, such as steroid-sparing regimens, appear beneficial whereas mTORi- and cyclosporine-based maintenance are associated with greater potential for adverse effects. Prospective clinical trials to assess the safety and efficacy of immunosuppression agents in older recipients are urgently needed.

Pharmacokinetic Model Analysis of Supralingual, Oral and Intravenous Deliveries of Mycophenolic Acid

Mycophenolic acid (MPA) is commonly used for organ rejection prophylaxis via oral administration in the clinic. Recent studies have shown that MPA also has anticancer activities. To explore new therapeutic options for oral precancerous/cancerous lesions, MPA was designed to release topically on the dorsal tongue surface via a mucoadhesive patch. The objective of this study was to establish the pharmacokinetic (PK) and tongue tissue distribution of mucoadhesive MPA patch formulation after supralingual administration in rats and also compare the PK differences between oral, intravenous, and supralingual administration of MPA. Blood samples were collected from Sprague Dawley rats before and after a single intravenous bolus injection, a single oral dose, or a mucoadhesive patch administration on the dorsal tongue surface for 4 h, all with a dose of 0.5 mg/kg of MPA. Plots of MPA plasma concentration versus time were obtained. As multiple peaks were found in all three curves, the enterohepatic recycling (EHR) model in the Phoenix software was adapted to describe their PK parameters with an individual PK analysis method. The mean half-lives of intravenous and oral administrations were 10.5 h and 7.4 h, respectively. The estimated bioavailability after oral and supralingual administration was 72.4% and 7.6%, respectively. There was a 0.5 h lag-time presented after supralingual administration. The results suggest that the systemic plasma MPA concentrations were much lower in rats receiving supralingual administration compared to those receiving doses from the other two routes, and the amount of MPA accumulated in the tongue after patch application showed a sustained drug release pattern. Studies on the dynamic of drug retention in the tongue after supralingual administration showed that ~3.8% of the dose was accumulated inside of tongue right after the patch removal, ~0.11% of the dose remained after 20 h, and ~20.6% of MPA was not released from the patches 4 h after application. The data demonstrate that supralingual application of an MPA patch can deliver a high amount of drug at the site of administration with little systemic circulation exposure, hence lowering the potential gastrointestinal side effects associated with oral administration. Thus, supralingual administration is a potential alternative route for treating oral lesions.

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.

Population Pharmacokinetic Model of Plasma and Cellular Mycophenolic Acid in Kidney Transplant Patients from the CIMTRE Study

Background and Objective

Mycophenolate mofetil is widely used in kidney transplant recipients. Mycophenolate mofetil is hydrolysed by blood esterases to mycophenolic acid (MPA), the active drug. Although MPA therapeutic drug monitoring has been recommended to optimise the treatment efficacy by the area under the plasma concentration vs time curve, little is known regarding MPA concentrations in peripheral blood mononuclear cells, where MPA inhibits inosine monophosphate dehydrogenase. This study aimed to build a pharmacokinetic model using a population approach to describe MPA total and unbound concentrations in plasma and into peripheral blood mononuclear cells in 78 adult kidney transplant recipients receiving mycophenolate mofetil therapy combined with tacrolimus and prednisone.

Methods

Total and unbound plasma concentrations and peripheral blood mononuclear cell concentrations were assayed. A three-compartment model, two for plasma MPA and one for peripheral blood mononuclear cell MPA, with a zero-order absorption and a first-order elimination was used to describe the data.

Results

Mycophenolic acid average concentrations in peripheral blood mononuclear cells were well above half-maximal effective concentration for inosine monophosphate dehydrogenase and no relationship was found with the occurrence of graft rejection. Three covariates affected unbound and intracellular MPA pharmacokinetics: creatinine clearance, which has an effect on unbound MPA clearance, human serum albumin, which influences fraction unbound MPA and the ABCB1 3435 C>T (rs1045642) genetic polymorphism, which has an effect on MPA efflux transport from peripheral blood mononuclear cells.

Conclusion

This population pharmacokinetic model demonstrated the intracellular accumulation of MPA, the efflux of MPA out of the cells being dependent on P-glycoprotein transporters. Nevertheless, further studies are warranted to investigate the relevance of MPA concentrations in peripheral blood mononuclear cells to dosing regimen optimisation.

Electronic supplementary material

The online version of this article (10.1007/s40268-020-00319-y) contains supplementary material, which is available to authorized users.

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.

Mycophenolic acid area under the concentration-time curve is associated with therapeutic response in childhood-onset lupus nephritis

BACKGROUND

Mycophenolic acid (MPA), the active compound of mycophenolate mofetil (MMF), is widely used in lupus nephritis treatment. Therapeutic drug monitoring of adults suggests that area under the concentration-time curve (AUC) of MPA (MPA-AUC) is associated with clinical outcomes, but childhood data are scarce.

METHODS

Retrospective study of 27 children with biopsy-proven lupus nephritis treated with MMF between 2008 and 2016. In 25 children, MPA-AUC was performed within 6 months after kidney biopsy and MMF initiation. Treatment response at 6 months was defined as normal or improved GFR by 25% compared with baseline, 50% reduction of proteinuria to < 0.5 g/day or 50 mg/mmol, and no hematuria.

RESULTS

A total of 62 MPA-AUC were analyzed in 27 patients. Overall median was 44 mg h/L (interquartile range [IQR] 33-54). Individual dose adaptation was required in 32 cases (52%) to achieve target AUC of 30-60 mg h/L. At 6 months, 14/25 patients were defined as responders (56%, median MPA-AUC 49 mg h/L (40-59)) and 11/25 as non-responders (44%, 29 mg h/L (24-38)). Patients with MPA-AUC levels > 45, 30-45, and < 30 mg h/L had 6-month response rates of 89% (8/9), 60% (6/10), and 0% (0/6), respectively. In a logistic regression model adjusted for age, sex, lupus nephritis classification, and time since MMF initiation, an MPA-AUC > 45 mg h/L was significantly associated with therapeutic response (OR 3.6, 95% CI 2.4-9.5, p = 0.03).

CONCLUSIONS

Therapeutic drug monitoring leading to individualized dosing may improve efficacy of MMF. MPA-AUC > 45 mg h/L is associated with better response rate and may be considered as a target value in pediatric lupus nephritis.

Validated LC-MS/MS method for quantitation of total and free mycophenolic acid concentration and its application to a pharmacokinetic study in pediatric renal transplant recipients

A simple and sensitive LC-MS/MS method was established to quantify total and free mycophenolic acid (MPA) plasma concentrations during immunosuppressive medication for pediatric renal transplantation. The chromatographic separation was performed with the Hypersil GOLD C₁₈ column, using a mobile phase consisting of 0.1% formic acid in water and acetonitrile (60:40, v/v) at an isocratic flow rate of 0.4 ml/min. An Agilent 6420 triple quadrupole mass spectrometer was operated via a positive electrospray ionization interface using the transitions m/z 321.14 → 206.9 for MPA and m/z 324.15 → 209.9 for MPA-d3 (internal standard). The linearity was 0.1-50 μg/ml for total MPA and 0.0025-0.5 μg/ml for free MPA. The within-run and between-run precisions were all <5% and accuracy was within 96.23-107.63%. The validated method was successfully aspplied to a pharmacokinetic study in 28 pediatric renal recipients. The mean free fraction of MPA in our patients was 0.89% (ranging from 0.62 to 1.25%) and albumin level played a major role in the variability of free fraction of MPA, thus, in pediatric patients with hypoproteinemia, close free drug monitoring and dose adjustments should be considered to prevent toxicity.

The utility of trough mycophenolic acid levels for the management of lupus nephritis

Background

Monitoring of mycophenolic acid (MPA) levels may be useful for effective mycophenolate mofetil (MMF) dosing. However, whether commonly obtained trough levels are an acceptable method of surveillance remains debatable. We hypothesized that trough levels of MPA would be a poor predictor of area under the curve (AUC) for MPA.

Methods

A total of 51 patients with lupus nephritis who were on MMF 1500 mg twice a day and had a 4-h AUC done were included in this study. MPA levels were measured prior to (C0) and at 1 (C1), 2 (C2) and 4 (C4) h, followed by 1500 mg of MMF. The MPA AUC values were calculated using the linear trapezoidal rule. Regression analysis was used to examine the relationship between the MPA trough and AUC. Differences in the MPA trough and AUC between different clinical and demographic categories were compared using t-tests.

Results

When grouped by tertiles there was significant overlap in MPA, AUC 0-4 and MPA trough in all tertiles. Although there was a statistically significant correlation between MPA trough levels and AUC, this association was weak and accounted for only 30% of the variability in MPA trough levels. This relationship might be even more unreliable in men than women. The use of angiotensin-converting enzyme inhibitors or angiotensin receptor blockers was associated with increased MPA trough levels and AUC at 0-4 h (AUC0-4).

Conclusion

Trough levels of MPA do not show a strong correlation with AUC. In clinical situations where MPA levels are essential to guide therapy, an AUC0-4 would be a better indicator of the adequacy of treatment.

Prediction of Free from Total Mycophenolic Acid Concentrations in Stable Renal Transplant Patients: A Population-Based Approach

BACKGROUND

A population pharmacokinetic (PK) protein-binding model was developed to (1) predict free mycophenolic acid (fMPA) based on total MPA (tMPA) concentrations in renal transplant patients, to establish the therapeutic range of fMPA through pharmacokinetic-pharmacodynamic studies; and (2) provide a guideline for dosing mycophenolate mofetil (MMF).

METHODS

Full PK profiles of 56 patients (from five different occasions) during the first year after transplantation who were treated with oral MMF and cyclosporine, or macrolides (either tacrolimus or sirolimus), were analysed. fMPA protein-binding was modelled using nonlinear mixed effects modelling (NONMEM). The influence of physiological factors and coadministered immunosupressant was studied.

RESULTS

A two-compartment model with first-order absorption and elimination, linear protein binding and enterohepatic circulation (EHC) best described the PK of MPA. Different recycling rate constants were considered depending on the coadministered immunosuppressant. The protein-binding rate constant (K_B [relative standard error, RSE%]) increased nonlinearly with renal function according to K _B = 43.1 (3.13)·(CL_CR/59.51)^0.394(10.66) h^-1. Furthermore, fMPA plasma clearance, given by clearance of the free mycophenolic acid (CL_fMPA), CL_fMPA = 410 (RSE%3.00)·(1+CsA·0.594 (22.39)) L/h, was 59.4% greater in cyclosporine-treated patients than in macrolide-treated patients, leading to lower MPA exposures. External evaluation proved acceptable area under the plasma concentration-time curve and trough concentration predictions.

CONCLUSIONS

A reliable protein-binding population PK model was developed for prediction of fMPA or tMPA from each other and for dose guiding in stable renal transplant recipients.

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.

High plasma mycophenolate acid concentration in the early phase of induction therapy predicts good renal outcome in lupus nephritis

Objectives: To identify the prognostic predictive factor of complete renal response (CR) at week 12 by focusing on the plasma mycophenolic acid (MPA) concentration in induction therapy in lupus nephritis.Methods: We prospectively enrolled patients with biopsy-proven LN class III/IV who were hospitalized between 2016 and 2017. As an induction therapy, mycophenolate mofetil was continuously introduced at 2000 mg/day. We measured the MPA plasma concentration at two time points depending on the induction therapy phase, early (week 4) or middle (week 12). The association between these concentrations and CR rate at week 12 was evaluated.Results: Ten patients were enrolled. A significantly higher AUC_0-12 between 0 and 12 h of MPA at the early phase was observed in the patients with CR at week 12 than in those without (p = .03). All the patients with high MPA-AUC_0-12 (> 40 mg h/L) at the early phase achieved CR at week 12, but no such association was found at the middle phase. The multivariate analysis revealed that MPA-AUC0-12 was selected as an independent predictive factor of CR at week 12 (odds ratio: 1.12; 95% confidence interval: 1.01-1.45, p = .02).Conclusion: The high AUC_0-12 of MPA at the early phase of induction therapy may predict good renal response.

Early pharmacokinetics of low dosage mycophenolate exposure in Thai kidney transplant recipients

Background The effects of mycophenolic acid exposure in the early period after transplantation on clinical outcomes have been reported; however, mycophenolic acid exposure in the early period after transplantation in Asian kidney transplant recipients who receive 1.5 g/d mycophenolate mofetil has never been investigated. Objective To determine mycophenolic acid exposure on day 3 post-transplantation in kidney transplant recipiens who receive 1.5 g/d mycophenolate mofetil. The effects of the reduced renal function on mycophenolic acid area under the concentration-time curve (AUC) and the achievement of the target AUC on the incidence of biopsy proven acute rejection during the first month post-transplantation were also evaluated. Setting A university hospital Method Blood samples and 24-h urine were collected on day 3 post-transplantation. Main outcome measures The mycophenolic acid AUC was calculated by linear trapezoidal rule and compared with the target of 45 mg*h/L. Results Of 42 Thai kidney transplant recipiens, the mean mycophenolic acid AUC of 45.1 mg*h/L (SD 14.7) was comparable to the AUC target (P = 0.962). Significant differences of the mycophenolic acid AUC were observed between patients with urine output of < 2400 mL and those with urine output ≥ 2400 mL (35.3 ± 6.6 and 47.4 ± 15.2, respectively; P = 0.002), and between patients with 24-h measured CrCl < 25 mL/min and those with CrCl ≥ 25 mL/min (38.0 (29.0, 42.2) and 49.2 ± 14.0, respectively; P = 0.017). Proportions of overall biopsy proven acute rejection among patients with mycophenolic acid AUC of < 45 and ≥ 45 mg*h/L were comparable (20.0% and 23.5%, respectively; P = 1.000). Conclusions After the starting dosage of 1.5 g/d mycophenolate mofetil, the mean mycophenolic acid AUC on day 3 post-kidney transplantation is comparable with the target of 45 mg*h/L. Severely reduced renal function significantly influences mycophenolic acid exposure.

Immunosuppressive drugs and the gastrointestinal tract in renal transplant patients

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

Impact of UGT2B7 and ABCC2 genetic polymorphisms on mycophenolic acid metabolism in Chinese renal transplant recipients

AIM

To evaluate genetic variants affecting mycophenolic acid (MPA) metabolism in Chinese renal transplant recipients.

METHODS

Total 11 SNPs of UGT1A9, UGT1A8, UGT2B7, ABCC2, ABCG2 and SLCO1B3 were genotyped in 408 Chinese renal transplant recipients. Associations between SNPs and MPA concentration/dose ratio (C₀/D) were analyzed using different genetic models. Multivariate linear regression was used to analyze associations between log (C₀/D) and clinical factors. Results: After adjustment by clinical factors, UGT2B7 rs7662029 was associated with log (C₀/D) using a dominant (p = 0.041) and an additive (p = 0.038) model, ABCC2 rs717620 was associated with log (C₀/D) using a recessive model (p = 0.019). Using additive model, SNP-SNP interactions were identified (p = 0.002) between ABCC2 rs717620 and UGT1A9 rs2741049, with interactions (p = 0.002) between ABCC2 rs717620 and UGT1A8 rs1042597. Age, albumin and serum creatinine were associated with log (C₀/D).

CONCLUSION

rs7662029 and rs717620 may affect MPA pharmacokinetics. SNP-SNP interactions and clinical factors may have significant effects on MPA metabolism.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Inosine Monophosphate Dehydrogenase Pharmacogenetics in Hematopoietic Cell Transplantation Patients

We evaluated inosine monophosphate dehydrogenase (IMPDH) 1 and IMPDH2 pharmacogenetics in 247 recipient-donor pairs after nonmyeloablative hematopoietic cell transplant (HCT). Patients were conditioned with total body irradiation + fludarabine and received grafts from related or unrelated donors (10% HLA mismatch), with postgraft immunosuppression of mycophenolate mofetil (MMF) with a calcineurin inhibitor. Recipient and donor IMPDH genotypes (rs11706052, rs2278294, rs2278293) were not associated with day 28 T cell chimerism, acute graft-versus-host disease (GVHD), disease relapse, cytomegalovirus reactivation, nonrelapse mortality, or overall survival. Recipient IMPDH1 rs2278293 genotype was associated with a lower incidence of chronic GVHD (hazard ratio, .72; P = .008) in nonmyeloablative HCT recipients. Additional studies are needed to confirm these results with the goal of identifying predictive biomarkers to MMF that lower GVHD.

Development of a Formula to Correct Particle-Enhanced Turbidimetric Inhibition Immunoassay Values so That it More Precisely Reflects High-Performance Liquid Chromatography Values for Mycophenolic Acid

Background

Mycophenolic acid (MPA) concentration measured by homogeneous particle-enhanced turbidimetric inhibition immunoassay (PETINA) may be overestimated due to its cross-reactivity with pharmacologically inactive MPA glucuronide (MPAG), as well as other minor metabolites, accumulated with renal function impairment or co-administered cyclosporine A. In contrast, high-performance liquid chromatography (HPLC) is precise because it can exclude the cross-reactivity. In this study, we assumed HPLC values for MPA (HPLC-MPA) as a reference and aimed to develop a formula correcting PETINA values for MPA (PETINA-MPA) to more precisely reflect HPLC-MPA.

Methods

MPA trough concentrations were measured both by HPLC-UV and PETINA in 39 samples issued from 39 solid-organ transplant recipients. MPAG concentrations were also measured using HPLC UV assay. We determined the impacts of renal function and coadministered calcineurin inhibitor on concentrations of MPA and MPAG measured by HPLC. Then, we evaluated the difference between PETINA-MPA and HPLC-MPA. Finally, we develop a formula to reflect HPLC-MPA by using multilinear regression analysis.

Results

MPAG concentration was negatively correlated with estimated glomerular filtration rate (eGFR) (R² = 0.376, P < 0.001), although MPA was not correlated with eGFR. There were no significant differences in MPA or MPAG concentrations per dose between the patients who were co-administered tacrolimus versus cyclosporine A. Finally, we developed the formulas to reflect HPLC-MPA:Formula 1: Estimated MPA concentration = 0.048 + 0.798 × PETINA-MPAFormula 2: Estimated MPA concentration = - 0.059 + 0.800 × PETINA-MPA + 0.002 × eGFRHowever, there was no significant improvement in the coefficient of determination with addition of eGFR in the formula, suggesting that HPLC-MPA can be well predicted by only 1 variable, PETINA-MPA.

Conclusions

This study developed a formula so that PETINA-MPA can be corrected to more precisely reflect HPLC-MPA.

Clinical Implication of Mycophenolic Acid Trough Concentration Monitoring in Kidney Transplant Patients on a Tacrolimus Triple Maintenance Regimen: A Single-Center Experience

Background

This study was designed to analyze the clinical implications of mycophenolic acid trough concentration monitoring.

Material/Methods

We collected data of patients with mycophenolic acid trough concentration monitoring after their first kidney transplant between November 2006 and March 2015 who were prescribed tacrolimus, mycophenolate, and methylprednisolone. Analyses were performed on 3 periods: 1 month, 1 month to 1 year, and after 1 year post-transplantation. To analyze factors related to acute cellular rejection, logistic regression was used for 1 month, while Cox analysis was used during 1 month to 1 year and after 1 year post-transplantation.

Results

In the 145 patients receiving mycophenolate mofetil, mean tacrolimus trough ≥7.0 ng/mL (OR=0.177, CI=0.060–0.524, p=0.002) and mean mycophenolic acid trough ≥1.7 mg/L (OR=0.190, CI=0.040–0.896, p=0.036) were protective for rejection during 1 month. Mean mycophenolic acid trough ≥1.7 mg/L (HR=0.179, CI=0.040–0.806, p=0.025) and ≥0.7 mg/L (HR=0.142, CI=0.028–0.729, p=0.019) were related to better rejection-free survival during 1 month to 1 year and after 1 year, respectively. In 399 patients receiving enteric-coated mycophenolate sodium, mean tacrolimus trough ≥7.0 ng/mL (OR=0.258, CI=0.131–0.507, p<0.001) and mean mycophenolic acid trough ≥2.1 mg/L (OR=0.507, CI=0.264–0.973, p=0.041) were protective for rejection during 1 month. Mean mycophenolic acid trough ≥1.7 mg/L (HR=0.519, CI=0.289–0.932, p=0.028) and ≥0.7 mg/L (HR=0.208, CI=0.072–0.602, p=0.004) were related to better rejection-free survival during 1 month to 1 year and after 1 year, respectively.

Conclusions

Mycophenolic acid trough concentration monitoring can be useful in preventing acute cellular rejection in patients receiving tacrolimus, mycophenolate, and methylprednisolone.

Pharmacokinetic Variability of Mycophenolic Acid in Pediatric and Adult Patients With Hematopoietic Stem Cell Transplantation

The aim of this study was to evaluate the pharmacokinetic variations of mycophenolic acid (MPA), the active metabolite of mycophenolate mofetil (MMF), in both pediatric and adult patients following hematopoietic stem cell transplantation (HSCT). Twenty pediatric patients with a median age of 3 years (range 0.2-12 years) and 13 adult patients with a median age of 54 years (range 18-63 years) were enrolled. Blood samples were collected on days 0, 7, 14, 21, and 30 after allogeneic HSCT. Total and free (unbound) MPA as well as MPA 7-O-glucuronide (MPAG) were quantified using a validated LC-MS/MS assay. The plasma protein binding of MPA and MPAG did not change significantly in pediatric patients over the 1-month sampling period post-HSCT. However, it increased in adult patients from day 7 to day 30 post-HSCT, from 97.3 ± 0.8% to 98.3 ± 0.6% for MPA (P < .05), and 74.6 ± 9.4% to 82.9 ± 8.1% for MPAG (P < .05). The plasma protein binding of MPA was significantly higher in males compared to females in both pediatric (98.3 ± 1.1% vs 97.4 ± 1.1%) and adult (98.1 ± 0.7% vs 97.4 ± 1.2%) patients (P < .05). The MPAG/MPA ratios on a milligram-per-kilogram dose basis in adult patients were significantly higher than those in pediatric patients (4.3 ± 3.4 vs 2.4 ± 2.6; P < .05). Time-dependent plasma protein binding and age-related differences in MPA metabolism at least in part impact the reported large intra- and interindividual variability in MPA pharmacokinetics. These patient and pharmacologic factors, if incorporated into MMF regimen design and modification, may contribute to the rational dose selection of MMF in HSCT patients.

Nonlinear relationship between enteric-coated mycophenolate sodium dose and mycophenolic acid exposure in Han kidney transplantation recipients

The aim of the research was to investigate the pharmacokinetics (PK) of enteric-coated mycophenolate sodium (EC-MPS) by quantification of the active metabolite of mycophenolic acid (MPA) after multiple escalating oral doses in Han kidney transplant recipients. A total of 28 Han postoperative kidney transplant recipients were given a multiple-dose of 540, 720 or 900 mg of EC-MPS two times a day in combination with tacrolimus for 6 days. Blood specimens were collected at each time point from 0 to 12 h after EC-MPS administration. MPA plasma concentrations were measured by UPLC—UV. The relationship between the EC-MPS dose and its PK parameters was assessed. In the range from 540 to 900 mg, C_max and AUC_0—12h did not increase with dose escalation. The AUC_0—12h, C_max, C₀ and T_max for the 540 720 and 900 mg doses were not significantly different, respectively (P >0.05). AUC_0—12 h and C_max were increased less than proportionally with increasing EC-MPS dose levels. Inter-individual variability in AUC_0—12h, C_max and C₀ were considerable. Nonlinear PK relationships were found from the doses of 540–900 mg of EC-MPS.

Pharmacokinetics, Pharmacodynamics, and Pharmacogenomics of Immunosuppressants in Allogeneic Hematopoietic Cell Transplantation: Part II

Part I of this article included a pertinent review of allogeneic hematopoietic cell transplantation (alloHCT), the role of postgraft immunosuppression in alloHCT, and the pharmacokinetics, pharmacodynamics, and pharmacogenomics of the calcineurin inhibitors and methotrexate. In this article (Part II), we review the pharmacokinetics, pharmacodynamics, and pharmacogenomics of mycophenolic acid (MPA), sirolimus, and the antithymocyte globulins (ATG). We then discuss target concentration intervention (TCI) of these postgraft immunosuppressants in alloHCT patients, with a focus on current evidence for TCI and on how TCI may improve clinical management in these patients. Currently, TCI using trough concentrations is conducted for sirolimus in alloHCT patients. Several studies demonstrate that MPA plasma exposure is associated with clinical outcomes, with an increasing number of alloHCT patients needing TCI of MPA. Compared with MPA, there are fewer pharmacokinetic/dynamic studies of rabbit ATG and horse ATG in alloHCT patients. Future pharmacokinetic/dynamic research of postgraft immunosuppressants should include '-omics'-based tools: pharmacogenomics may be used to gain an improved understanding of the covariates influencing pharmacokinetics as well as proteomics and metabolomics as novel methods to elucidate pharmacodynamic responses.

1-Alpha, 25-dihydroxyvitamin D3 alters the pharmacokinetics of mycophenolic acid in renal transplant recipients by regulating two extrahepatic UDP-glucuronosyltransferases 1A8 and 1A10

Mycophenolic acid (MPA) is an important immunosuppressant broadly used in renal transplantation. However, the large inter-patient variability in mycophenolic acid (MPA) pharmacokinetics (PK) limits its use. We hypothesize that extrahepatic metabolism of MPA may have significant impact on MPA PK variability. Two intestinal UDP-glucuronosyltransferases 1A8 and 1A10 plays critical role in MPA metabolism. Both in silico and previous genome-wide analyses suggested that vitamin D (VD) may regulate intestinal UGT1A expression. We validated the VD response elements (VDREs) across the UGT1A locus with chromatin immunoprecipitation (ChIP) and luciferase reporter assays. The impact of 1-alpha,25-dihydroxyvitamin D3 (D3) on UGT1A8 and UGT1A10 transcription and on MPA glucuronidation was tested in human intestinal cell lines LS180, Caco-2 and HCT-116. The correlation between transcription levels of VD receptor (VDR) and the two UGT genes were examined in human normal colorectal tissue samples (n = 73). PK alterations of MPA following the parent drug, mycophenolate mofetil (MMF), and D3 treatment was assessed among renal transplant recipients (n = 10). Our ChIP assay validate three VDREs which were further demonstrated as transcriptional enhancers with the luciferase assays. D3 treatment significantly increased transcription of both UGT genes as well as MPA glucuronidation in cells. The VDR mRNA level was highly correlated with that of both UGT1A8 and UGT1A10 in human colorectal tissue. D3 treatment in patients led to about 40% reduction in both AUC_0-12 and Cmax while over 70% elevation of total clearance of MPA. Our study suggested a significant regulatory role of VD on MPA metabolism and PK via modulating extrahepatic UGT activity.

The pharmacokinetics and pharmacodynamics of mycophenolate mofetil in younger and elderly renal transplant recipients

AIMS

Elderly transplant recipients have a lower incidence of acute rejection, and a higher risk to die from infectious complications. A potential cause may be differences in the pharmacokinetics (PK) or pharmacodynamics (PD) of the immunosuppressive drugs they are taking. This study was designed to comprehensively evaluate the influence of age on the PK and PD of mycophenolic acid (MPA).

METHODS

In this study the PK and PD of MPA was studied in 26 elderly and 54 younger renal transplant recipients treated with mycophenolate mofetil and tacrolimus. Patients were sampled repetitively, both before and during the first 6 months after kidney transplantation. Age-related variability in MPA PK, baseline IMPDH activity, as well as MPA-induced IMPDH inhibition were studied.

RESULTS

The IMPDH activity pre-transplantation did not differ between elderly and younger patients. Neither IMPDH activity pre-transplantation nor maximum IMPDH inhibition was significantly correlated with the patients' age. The area under the MPA plasma concentration-time curve (AUC_0-12h ) and the area under the effect (IMPDH activity)-time curve (AEC_0-12h ) from 0 to 12 h were also not significantly different between the two groups. We found no significant differences in EC₅₀ and E_max between elderly and younger patients.

CONCLUSIONS

Age did not significantly affect the PK or PD of MPA. It is unlikely that the lower incidence of acute rejection in elderly patients, or the higher risk to die from a severe infection in elderly patients is due to different handling of MPA in the elderly.

Limited sampling strategy for predicting area under the concentration-time curve for mycophenolic Acid in Chinese adults receiving mycophenolate mofetil and tacrolimus early after renal transplantation

BACKGROUND

The objective of the study was to investigate the pharmacokinetics of mycophenolate mofetil (MMF) in Chinese adults early after renal transplantation by an enzyme multiplied immunoassay technique and to establish a limited sampling strategy to predict the area under the concentration-time curve for plasma levels of mycophenolic acid (MPA-AUC).

METHODS

Fifty-eight recipients who underwent renal transplantation with an organ donated after cardiac death used a triple immunosuppressant strategy of MMF, tacrolimus, and prednisone. On the seventh day posttransplantation, plasma samples were collected at 0 hours (pre-dose) and at 0.5, 1, 1.5, 2, 4, 6, 8, 10, and 12 hours postdose (C0h, C0.5h, C1h, C1.5h, C2h, C4h, C6h, C8h, C10h, and C12h, respectively). Enzyme multiplied immunoassay technique was used to measure mycophenolic acid concentration, and model equations were generated by multiple stepwise regression analysis to determine MPA-AUC0-12h.

RESULTS

The 3-point equation obtained by multiple linear regression analysis was MPA-AUC = 7.951 + 4.04C6h + 1.893C2h + 4.542C10h (adjusted r = 0.863); the 4-point equation was MPA-AUC = 4.272 + 4.074C6h + 1.896C2h + 4.680C10h + 0.859C0.5h (adjusted r = 0.918). The % mean prediction error, % mean absolute error, and % root mean squared prediction error for the best-fit formula using C6h, C2h, C10h, and C0.5h were -0.2%, 8.7%, and 14.2%, respectively.

CONCLUSIONS

In Chinese adults receiving MMF and tacrolimus early after renal transplantation, the best equation for predicting MPA-AUC0-12h is 4.272 + 4.074C6h + 1.896C2h + 4.680C10h + 0.859C0.5h.

Pharmacokinetics of mycophenolic acid in children with clinically stable idiopathic nephrotic syndrome receiving cyclosporine

BACKGROUND

The suitable dosage regime of mycophenolate mofetil (MMF) based on the pharmacokinetics of mycophenoric acid (MPA) for pediatric patients with idiopathic nephrotic syndrome (INS) is controversial. The pharmacokinetics of MPA is influenced by renal function, serum albumin concentration, and concomitant medications, especially calcineurin inhibitors. This study analyzed the pharmacokinetics of MPA in clinically stable children with INS receiving cyclosporine (CyA).

METHODS

This retrospective study enrolled children with INS receiving MMF (Cellcept^®) (30-40 mg/kg/day in two divided doses) combined with CyA (Neoral^®) without relapse and renal dysfunction. Pharmacokinetic parameters, including the area under the concentration-time curve (AUC) calculated by the trapezoid method, were calculated from seven serial blood samples.

RESULTS

Thirty-two patients (22 males) of median age 11.0 years were included; 32 pharmacokinetic studies were performed. The median MMF dose was 16.2 mg/kg/time or 470.4 mg/m²/time. The median AUC0-12 was 44.3 ng h/mL. AUC0-12 of all patients showed excellent correlations with C2 (r ²  = 0.6405, P < 0.0001), resulting in a regression formula of AUC0-12 = 21.971 + 2.6059 C2. Comparisons of dose/body weight-normalized AUC0-12 values among age groups showed a lower value in the youngest group (≤5 years).

CONCLUSION

In children with clinically stable INS receiving CyA, C2 monitoring was the most useful single parameter for estimating MPA pharmacokinetics. Younger children required higher MMF doses.

Use of Glucuronidated Mycophenolic Acid Levels for Therapeutic Monitoring in Pediatric Lupus Nephritis Patients

BACKGROUND/OBJECTIVES

Mycophenolate mofetil (MMF) is used to treat pediatric-onset lupus nephritis (pLN). Data are equivocal on the use of plasma mycophenolic acid (MPA) levels as a measure of efficacy and predictor of therapeutic outcomes in pLN. Glucuronidated MPA (MPA-G) is an inactive metabolite that is a marker of adequate absorption and normal metabolism of MMF. We evaluated the use of MPA and MPA-G levels in routine care of pLN.

METHODS

This was a retrospective study of pLN patients treated with MMF dosed at 600 mg/m. Clinical renal remission (CR) was defined as proteinuria of less than 500 mg/24 h. Midinterval MPA and MPA-G plasma levels were drawn during routine follow-up, approximately 6 hours after the previous dose of MMF. Steady-state levels of MPA were calculated using pharmacokinetics and compared with routine midinterval plasma MPA levels.

RESULTS

Seventeen pLN patients treated with MMF had MPA and MPA-G levels. Eleven patients were in CR; 6 were not in CR at the time of evaluation and had not responded to MMF after more than 3 months of therapy. The mean MPA level for patients in CR was 3.26 ± 2.02 μg/mL compared with 3.02 ± 1.76 μg/mL for patients not in CR. Three patients in CR did not have detectable levels of MPA. Calculated steady-state levels of MPA did not reflect the observed levels. Glucuronidated MPA levels were therapeutic (44.2 ± 26.7 μg/mL) in patients in CR, but low (29.88 ± 22 μg/mL) in patients not in CR (not statistically significant).

CONCLUSIONS

Midinterval plasma levels of MPA do not reflect predicted steady-state levels in pLN and do not correlate with clinical response. Midinterval plasma levels of MPA-G indicate adequate absorption and may correlate better with clinical pLN activity.

A Rationale for Age-Adapted Immunosuppression in Organ Transplantation

Demographic changes are associated with a steady increase of older patients with end-stage organ failure in need for transplantation. As a result, the majority of transplant recipients are currently older than 50 years, and organs from elderly donors are more frequently used. Nevertheless, the benefit of transplantation in older patients is well recognized, whereas the most frequent causes of death among older recipients are potentially linked to side effects of their immunosuppressants.Immunosenescence is a physiological part of aging linked to higher rates of diabetes, bacterial infections, and malignancies representing the major causes of death in older patients. These age-related changes impact older transplant candidates and may have significant implications for an age-adapted immunosuppression. For instance, immunosenescence is linked to lower rates of acute rejections in older recipients, whereas the engraftment of older organs has been associated with higher rejection rates. Moreover, new-onset diabetes mellitus after transplantation is more frequent in the elderly, potentially related to corticosteroids, calcineurin inhibitors, and mechanistic target of rapamycin inhibitors.This review presents current knowledge for an age-adapted immunosuppression based on both, experimental and clinical studies in and beyond transplantation. Recommendations of maintenance and induction therapy may help to improve graft function and to design future clinical trials in the elderly.

Influence of sex and race on mycophenolic acid pharmacokinetics in stable African American and Caucasian renal transplant recipients

BACKGROUND AND OBJECTIVES

No evaluation of sex and race influences on mycophenolic acid (MPA) pharmacokinetics and adverse effects (AEs) during enteric-coated mycophenolate sodium (ECMPS) and tacrolimus immunosuppression are available. The primary objective of this study was to investigate the influence of sex and race on MPA and MPA glucuronide (MPAG) pharmacokinetics in stable renal transplant recipients receiving ECMPS and tacrolimus

METHODS

The pharmacokinetics of MPA and MPAG and their associated gastrointestinal AEs were investigated in 67 stable renal transplant recipients: 22 African American males (AAMs), 13 African American females (AAFs), 16 Caucasian males (CMs), and 16 Caucasian females (CFs) receiving ECMPS and tacrolimus. A validated gastrointestinal AE rating included diarrhea, dyspepsia, vomiting, and acid-suppressive therapy was completed. Apparent clearance, clearance normalized to body mass index (BMI), area under the concentration-time curve from time zero to 12 h (AUC12) and dose-normalized AUC12 (AUC*) were determined using a statistical model that incorporated gastrointestinal AE and clinical covariates.

RESULTS

Males had more rapid apparent MPA clearance (CMs 13.8 ± 6.27 L/h vs. AAMs 10.2 ± 3.73 L/h) than females (CFs 8.70 ± 3.33 L/h and AAFs 9.71 ± 3.94 L/h; p = 0.014) with a race-sex interaction (p = 0.043). Sex differences were observed in MPA clearance/BMI (p = 0.033) and AUC* (p = 0.033). MPA AUC12 was greater than 60 mg·h/L in 57 % of renal transplant recipients (RTR) with 71 % of patients demonstrating gastrointestinal AEs and a higher score noted in females. In all patients, females exhibited 1.40-fold increased gastrointestinal AE scores compared with males (p = 0.024). Race (p = 0.044) and sex (p = 0.005) differences were evident with greater MPAG AUC12 in AAFs and CFs.

CONCLUSION

Sex and race differences were evident, with females having slower MPA clearance, higher MPAG AUC12, and more severe gastrointestinal AEs. These findings suggest sex and race should be considered during MPA immunosuppression.