Therapeutic Drug Monitoring Of Mycophenolic Acid Research Articles

Limited Sampling Strategies Fail to Accurately Predict Mycophenolic Acid Area Under the Curve in Kidney Transplant Recipients and the Impact of Enterohepatic Recirculation.

Therapeutic drug monitoring for mycophenolic acid (MPA) is challenging due to difficulties in measuring the area under the curve (AUC). Limited sampling strategies (LSSs) have been developed for MPA therapeutic drug monitoring but come with risk of unacceptable performance. The authors hypothesized that the poor predictive performance of LSSs were due to the variability in MPA enterohepatic recirculation (EHR). This study is the first to evaluate LSSs models performance in the context of EHR. Adult kidney transplant recipients (n = 84) receiving oral mycophenolate mofetil underwent intensive MPA pharmacokinetic sampling. MPA AUC0-12hr and EHR were determined. Published MPA LSSs in kidney transplant recipients receiving tacrolimus were evaluated for their predictive performance in estimating AUC0-12hr in our full cohort and separately in individuals with high and low EHR. None of the evaluated LSS models (n = 12) showed good precision or accuracy in predicting MPA AUC0-12hr in the full cohort. In the high EHR group, models with late timepoints had better accuracy but low precision, except for 1 model with late timepoints at 6 and 10 hours postdose, which had marginally acceptable precision. For all models, the good guess of predicted AUC0-12hr (±15% of observed AUC0-12hr) was highly variable (range, full cohort = 19%-61.9%; high EHR = 4.5%-65.9%; low EHR = 27.5%-62.5%). The predictive performance of the LSS models varied according to EHR status. Timepoints ≥5 hours postdose in LSS models are essential to capture EHR. Models and strategies that incorporate EHR during development are required to accurately ascertain MPA exposure.

Vibrational study of mycophenolic acid and its quantification with electrochemically assisted surface-enhanced Raman spectroscopy

Mycophenolic acid (MPA) is an immunosuppressant widely used in transplantations, for which therapeutic drug monitoring (TDM) has proven beneficial. There is furthermore a need to develop affordable, rapid, and benchtop analytical methods to perform TDM of MPA in a point-of-need setting. In this paper, we report for the first time the Raman fingerprint region and surface-enhanced Raman spectroscopy (SERS) vibrations of MPA through density functional theory calculations. The output of these simulations was compared with experimental data from electrochemically assisted SERS, i.e. application of a well-defined potential or sequence of potentials in SERS assays. The systematic electrochemically assisted SERS experimental study was carried out to understand the adsorption behaviour of MPA on gold nanopillars (AuNPs) when different potentials were applied. We found that MPA interacts with the AuNPs through its benzofuran heterocycle and carboxylic acid group. Applying different potentials on the SERS substrate resulted in band shifts, which we hypothesise to originate from molecular reorientation on the metal surface. Moreover, an electrochemically assisted SERS assay was developed and carried out on a portable Raman spectrometer. We show that MPA detection can be performed in less than 5 min in a clinically relevant concentration range (1 – 50 µM), with improved repeatability compared to a SERS assay without any applied potential (overall RSD decrease from 34.6 % to 18.5 %).

Mycophenolic acid therapeutic drug monitoring using area under the curve in pediatric heart transplant recipients.

Pharmacokinetics of mycophenolic acid (MPA) display substantial interpatient variability, with up to 10-fold difference of exposure in individual patients under a fixed-dose regimen. MPA trough level (C0) monitoring is common in clinical practice but has not proven sufficiently informative in predicting MPA exposure or patient outcomes, especially in children. No limited sampling strategies (LSSs) have been generated from pediatric heart transplant (HTx) recipients to estimate MPA AUC. Single-center, observational analysis of 135 de novo pediatric HTx recipients ≤21years old who underwent MPA AUC between 2011 and 2021. Median age was 4years (IQR .6-12.1). Median time from transplant to MPA AUC sampling was 15days (IQR 11-19). MMF doses (mg or mg/day) had low, negative Pearson correlation coefficients (r) while doses adjusted for weight or body surface area had low correlation with Trapezoidal MPA AUC0-24h (r=.3 and .383, respectively). MPA C0 had weak association (r=.451) with Trapezoidal MPA AUC0-24h . LSS with two pharmacokinetic sampling time points at 90 (C3 ) and 360 (C5 )min after MMF administration (estimated AUC0-24h =32.82+4.12×C3 +11.53×C5 ) showed strong correlation with Trapezoidal MPA AUC0-24h (r=.87). MMF at fixed or weight-adjusted doses, as well as MPA trough levels, correlate poorly with MPA AUC0-24h . We developed novel LSSs to estimate Trapezoidal MPA AUC from a large cohort of pediatric HTx recipients. Validation of our LSSs should be completed in a separate cohort of pediatric HTx recipients.

High-performance liquid chromatography with fluorescence detection for mycophenolic acid determination in saliva samples

BackgroundFor therapeutic drug monitoring (TDM) of mycophenolic acid (MPA), which is frequently proposed, saliva might be a suitable and easy-to-obtain biological matrix. The study aimed to validate an HPLC method with fluorescence detection for determining mycophenolic acid in saliva (sMPA) in children with nephrotic syndrome.MethodsThe mobile phase was composed of methanol and tetrabutylammonium bromide with disodium hydrogen phosphate (pH 8.5) at a 48:52 ratio. To prepare the saliva samples, 100 µL of saliva, 50 µL of calibration standards, and 50 µL of levofloxacin (used as an internal standard) were mixed and evaporated to dryness at 45 °C for 2 h. The resulting dry extract was reconstituted in the mobile phase and injected into the HPLC system after centrifugation. Saliva samples from study participants were collected using Salivette® devices.ResultsThe method was linear within the range of 5–2000 ng/mL, was selective with no carry-over effect and met the acceptance criteria for within-run and between-run accuracy and precision. Saliva samples can be stored for up to 2 h at room temperature, for up to 4 h at 4 °C, and for up to 6 months at − 80 °C. MPA was stable in saliva after three freeze–thaw cycles, in dry extract for 20 h at 4 °C, and for 4 h in the autosampler at room temperature. MPA recovery from Salivette® cotton swabs was within the range of 94–105%. The sMPA concentrations in the two children with nephrotic syndrome who were treated with mycophenolate mofetil were within 5–112 ng/mL.ConclusionsThe sMPA determination method is specific, selective, and meets the validation requirements for analytic methods. It may be used in children with nephrotic syndrome; however further studies are required to investigate focusing on sMPA and the correlation between sMPA and total MPA and its possible contribution to MPA TDM is required.Graphical abstract

Therapeutic Drug Monitoring of Mycophenolic Acid as a Precision Medicine Tool for Heart Transplant Patients: Results of an Observational Pharmacokinetic Pilot Study.

In the clinical practice management of heart transplant (HTx), the impact of calcineurin inhibitors co-administration on pharmacokinetics (PKs) of mycophenolic acid (MPA), mycophenolate mofetil (MMF) active drug, is not adequately considered. This retrospective study investigated full MPA-PK profiles by therapeutic drug monitoring (TDM) in 21 HTx recipients treated with MMF combined with cyclosporine (CsA) or tacrolimus (TAC) at a median time of 2.6 months post-transplant. The two treatment groups were compared. We described the main MPA-PK parameters in patients developing acute cellular rejection (ACR) and those who did not. Median dose-adjusted MPA-trough levels and MPA-AUC0–12h were higher in patients co-treated with TAC than with CsA (p = 0.0001 and p = 0.006, respectively). MPA-Cmax and Tmax were similar between the two groups, whereas the enterohepatic recirculation biomarker of MPA (MPA-AUC4–12h) was higher in the MMF and TAC group (p = 0.004). Consistently, MPA clearance was higher in the MMF and CsA group (p = 0.006). In total, 87.5% of ACR patients were treated with MMF and CsA, presenting a lower MPA-AUC0–12h (p = 0.02). This real-world study suggested the CsA interference on MPA-PK in HTx, evidencing the pivotal role of MPA TDM as a precision medicine tool in the early phase after HTx. A prospective study is mandatory to investigate this approach to HTx clinical outcomes.

Population Pharmacokinetics of Mycophenolic Acid in Renal Transplant Patients: A Comparison of the Early and Stable Posttransplant Stages.

Mycophenolic acid (MPA) is an antimetabolic immunosuppressive drug widely used in solid organ transplantation and autoimmune diseases. Pharmacokinetics (PK) of MPA demonstrates high inter- and intra-variability. The aim of this study was to compare the population PK properties of MPA in adult renal transplant patients in the early and stable post-transplant stages and to simulate an optimal dosing regimen for patients at different stages. A total of 51 patients in the early post-transplant period (1 week after surgery) and 48 patients in the stable state (5.5–10 years after surgery) were included in the study. In the two-compartment population PK model, CL/F (23.36 L/h vs. 10.25 L/h) and V/F (78.07 vs. 16.24 L) were significantly different between the two stages. The dose-adjusted area under the concentration time curve (AUCss,12h/dose) for patients in the early stage were significantly lower than those for patients in the stable state (40.83 ± 22.26 mg h/L vs. 77.86 ± 21.34 mg h/L; p < 0.001). According to Monte Carlo simulations, patients with 1.0–1.5 g of mycophenolate mofetil twice daily in the early phase and 0.50–0.75 g twice daily in the stable phase had a high probability of achieving an AUCss,12h of 30–60 mg h/L. In addition, limited sampling strategies showed that two 4-point models (C0-C1-C2-C4 and C1-C2-C3-C6) performed well in predicting MPA exposure by both Bayesian estimate and regression equation and could be applied in clinical practice to assist therapeutic drug monitoring of MPA.

Recent Advances in Therapeutic Drug Monitoring of Voriconazole, Mycophenolic Acid, and Vancomycin: A Literature Review of Pediatric Studies.

The review includes studies dated 2011–2021 presenting the newest information on voriconazole (VCZ), mycophenolic acid (MPA), and vancomycin (VAN) therapeutic drug monitoring (TDM) in children. The need of TDM in pediatric patients has been emphasized by providing the information on the differences in the drugs pharmacokinetics. TDM of VCZ should be mandatory for all pediatric patients with invasive fungal infections (IFIs). Wide inter- and intrapatient variability in VCZ pharmacokinetics cause achieving and maintaining therapeutic concentration during therapy challenging in this population. Demonstrated studies showed, in most cases, VCZ plasma concentrations to be subtherapeutic, despite the updated dosages recommendations. Only repeated TDM can predict drug exposure and individualizing dosing in antifungal therapy in children. In children treated with mycophenolate mofetil (MMF), similarly as in adult patients, the role of TDM for MMF active form, MPA, has not been well established and is undergoing continued debate. Studies on the MPA TDM have been carried out in children after renal transplantation, other organ transplantation such as heart, liver, or intestine, in children after hematopoietic stem cell transplantation or cord blood transplantation, and in children with lupus, nephrotic syndrome, Henoch-Schönlein purpura, and other autoimmune diseases. MPA TDM is based on the area under the concentration–time curve; however, the proposed values differ according to the treatment indication, and other approaches such as pharmacodynamic and pharmacogenetic biomarkers have been proposed. VAN is a bactericidal agent that requires TDM to prevent an acute kidney disease. The particular group of patients is the pediatric one. For this group, the general recommendations of the dosing may not be valid due to the change of the elimination rate and volume of distribution between the subjects. The other factor is the variability among patients that concerns the free fraction of the drug. It may be caused by both the patients’ population and sample preconditioning. Although VCZ, MMF, and VAN have been applied in pediatric patients for many years, there are still few issues to be solve regarding TDM of these drugs to ensure safe and effective treatment. Except for pharmacokinetic approach, pharmacodynamics and pharmacogenetics have been more often proposed for TDM.

Comparison of a Point-of-Care Testing with Enzyme-Multiplied Immunoassay Technique and Liquid Chromatography Combined With Tandem Mass Spectrometry Methods for Therapeutic Drug Monitoring of Mycophenolic Acid: A Preliminary Study.

For mycophenolic acid (MPA), therapeutic drug monitoring is an essential tool for dosage optimization in transplant recipients and autoimmune diseases. In China, a new commercial kit using an immunochromatographic assay (FICA) with a point-of-care testing system was approved for therapeutic drug monitoring of MPA. However, corroboration between FICA and clinically used assays remains unknown. The authors evaluated MPA concentrations in heart transplant recipients obtained by FICA, high-performance liquid chromatography combined with tandem mass spectrometry (LC-MS/MS), and enzyme-multiplied immunoassay technique (EMIT). Nine heart transplant recipients administered a single mycophenolate mofetil (MMF) dose, and 4 administered multiple MMF doses were enrolled. MPA samples were collected before administration, and after 0.5, 1, 1.5, 2, 4, 6, 8, 10, and 12 hours, and assessed by 2 immunoassays (EMIT and FICA) and LC-MS/MS. Consistency between methods was evaluated using Passing-Bablok regression and Bland-Altman analysis. For Passing-Bablok regression between FICA and LC-MS/MS, FICA = 0.784 LC-MS/MS + 0.360 (95% CI slope: 0.739 to 0.829, 95% CI intercept: 0.174-0.545). Regardless of a significant observed correlation coefficient (R2 = 0.9126), statistical analyses revealed a significant difference between FICA and the reference LC-MS/MS method. The mean absolute bias was 0.69 mcg/mL between FICA and LC-MS/MS. Bland-Altman plots showed a mean bias of -0.23 mcg/mL (±1.96 SD, -2.19 to 1.72 mcg/mL) and average relative bias of 14.73% (±1.96 SD, -67.91% to 97.37%) between FICA and LC-MS/MS. Unsatisfactory consistency was observed between EMIT and LC-MS/MS, and FICA and EMIT. Differences between pharmacokinetic parameters after a single or 7 days of MMF administration, by LC-MS/MS and FICA, were not statistically significant. The consistency of the new FICA using a point-of-care testing device with LC-MS/MS and EMIT was inadequate, and the accuracy of EMIT and LC-MS/MS was inappropriate. Clinicians should be informed when switching MPA detection methods to avoid misleading results.

Comparison between enzyme-multiplied immunoassay technique (EMIT) and high-performance liquid chromatography with ultraviolet detection (HPLC-UV) for the therapeutic drug monitoring of mycophenolic acid in Mexican pediatric patients with renal transplantation

Introduction. Mycophenolic acid (MPA) is an immunosuppressant; thus, monitoring of plasma levels is recommended. The most popular analytic methods used for the MPA quantification are the enzyme-multiplied immunoassay technique (EMIT) and the high-performance liquid chromatography with ultraviolet detection (HPLC-UV). The purpose of the present study was to compare both methods performances for the therapeutic drug monitoring of MPA in Mexican pediatric patients with renal transplantation. Material and Methods. A prospective cross‐sectional study was carried out, 25 patients with kidney transplantation were included. Mycophenolate mofetil was administered and blood samples were drawn at 0, 0.5, 1, 2, 3, 4, 6, 8, and 12 h after medication. Plasma samples were obtained and divided into two aliquots for further quantification by both methodologies. Each concentration determined by EMIT was compared with the corresponding quantification by HLPC-UV. Bias and precision were estimated as previously described by Sheiner and Beal. Results. EMIT overestimated MPA concentrations with a positive bias of 59.25% and a precision of 54.85%. AUC0-12, the recommended parameter for therapeutic drug monitoring of MPA, was significantly overestimated by EMIT in more than 50%. Discussion. Overestimation derives from metabolite cross-reactivity in EMIT, which does not occur with HPLC-UV. Hence, HPLC-UV appears to be a more suitable method for MPA therapeutic drug monitoring in Mexican pediatric patients with renal transplantation.

The Evaluation of Multiple Linear Regression-Based Limited Sampling Strategies for Mycophenolic Acid in Children with Nephrotic Syndrome.

We evaluated mycophenolic acid (MPA) limited sampling strategies (LSSs) established using multiple linear regression (MLR) in children with nephrotic syndrome treated with mycophenolate mofetil (MMF). MLR-LSS is an easy-to-determine approach of therapeutic drug monitoring (TDM). We assessed the practicability of different LSSs for the estimation of MPA exposure as well as the optimal time points for MPA TDM. The literature search returned 29 studies dated 1998–2020. We applied 53 LSSs (n = 48 for MPA, n = 5 for free MPA [fMPA]) to predict the area under the time-concentration curve (AUCpred) in 24 children with nephrotic syndrome, for whom we previously determined MPA and fMPA concentrations, and compare the results with the determined AUC (AUCtotal). Nine equations met the requirements for bias and precision ±15%. The MPA AUC in children with nephrotic syndrome was predicted the best by four time-point LSSs developed for renal transplant recipients. Out of five LSSs evaluated for fMPA, none fulfilled the ±15% criteria for bias and precision probably due to very high percentage of bound MPA (99.64%). MPA LSS for children with nephrotic syndrome should include blood samples collected 1 h, 2 h and near the second MPA maximum concentration. MPA concentrations determined with the high performance liquid chromatography after multiplying by 1.175 may be used in LSSs based on MPA concentrations determined with the immunoassay technique. MPA LSS may facilitate TDM in the case of MMF, however, more studies on fMPA LSS are required for children with nephrotic syndrome.

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.

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

Background and ObjectiveMycophenolate 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.MethodsTotal 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.ResultsMycophenolic 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.ConclusionThis 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 materialThe online version of this article (10.1007/s40268-020-00319-y) contains supplementary material, which is available to authorized users.

SAT-333 MYCOPHENOLIC ACID MONTTORNIC IN RENAL ALIOGRAFT RECIPIENTS; ASSOCIATATION WITH SAFETY AND EFFICACY

Mycophenolic acid (MPA) is one of the cornerstones immunosuppressants in the setting of transplantation. Advances in the pharmacokinetic studies have uncovered the high inter and intra_individual variability of plasma mycophenolic acid level. This variability in drug concentration can cause both supra therapeutic and sub therapeutic drug plasma levels which can have hazardous results in transplant patients. To date, routine therapeutic drug monitoring of MPA has not been established in clinical practice. Aim of the work: Our objective was to monitor the level of MPA in relation to the occurrence of gastrointestinal (GI) complications and renal function in renal allograft recipients. MPA trough level was measured in 51 renal allograft recipients at the entry of the study and 4 weeks after any dose modification. Levels were correlated with the side effects recorded during the study follow up period. GI toxicity, hematological toxicity and biopsy proven acute rejection (BPAR) were diagnosed in 29.4%, 9.8% and 11.7% of the studied population respectively. Higher MPA 12-hr trough levels were associated with hematological side effects, yet, the correlation with GI side effects was largely negative. A significant correlation between low MPA plasma levels and the development of BPAR after kidney transplantation was detected. An MPA level of 3.5 µg/mL best discriminated between patients who developed hematological toxicity from those who didn’t while MPA level of 2.4 µg/mL best discriminated between patients with and without BPAR. Monitoring of MPA trough level should be practiced in renal allograft recipients in order to avoid drug toxicity without compromising efficacy.

The development of a population physiologically based pharmacokinetic model for mycophenolic mofetil and mycophenolic acid in humans using data from plasma, saliva, and kidney tissue.

Mycophenolic acid (MPA) is used widely to prevent graft rejection in kidney-transplant patients. Therapeutic drug monitoring (TDM) in plasma requires an invasive procedure that is inconvenient, especially in pediatric patients. TDM in saliva is a more convenient non-invasive alternative compared with plasma. A population physiologically based pharmacokinetic (Pop-PBPK) model of mycophenolate mofetil (MMF) and MPA with enterohepatic recycling was built and verified using previously published plasma, saliva, and kidney biopsy data in healthy and kidney-transplant adult patients. The verified model was then used to predict experimentally observed plasma and saliva MMF and MPA TDM data in Jordanian pediatric kidney transplant patients measured using LC-MS/MS. A correlation was established between plasma and saliva exposures in pediatrics. The developed LCMS was sensitive to both MMF and MPA in plasma and saliva. The developed Pop-PBPK model predicted well the previously reported MMF and MPA levels in plasma, saliva, and kidney tissue and those observed in the current study (more than 75% of observed data points were within 90% predictive interval of population simulations). A statistically significant correlation was found between plasma and saliva exposures for both MMF (Pop-PBPK predicted and observed) and MPA (Pop-PBPK predicted). Both MPA and MMF can be classified as class III compounds in the Salivary Excretion Classification System. Saliva is an alternative body fluid to plasma that can be used for TDM of MPA and MMF in kidney-transplant patients in pediatrics. Exposure to MPA and MMF in plasma, saliva, and kidney tissue was reliably predicted using the developed Pop-PBPK model.

Investigation of the Association Between Total and Free Plasma and Saliva Mycophenolic Acid Concentrations Following Administration of Enteric-Coated Mycophenolate Sodium in Adult Kidney Transplant Recipients.

Mycophenolic acid (MPA) is commonly used following renal transplant. Saliva MPA concentrations may reflect the pharmacologically active form of MPA in plasma. Therapeutic drug monitoring using saliva is convenient and non-invasive. This study examined the correlation between total and free plasma and saliva MPA concentrations following enteric-coated mycophenolate sodium (EC-MS) administration in renal transplant recipients. Total and free plasma and saliva MPA concentrations were measured simultaneously in 20 adult renal transplant recipients 1-2months' post-transplant. Thirteen samples were taken pre-dose and at specified time points up until 12h post-dose. When considering all time points, correlation between total plasma and saliva MPA was r2 = 0.51 and between free plasma and saliva MPA concentrations r2 = 0.41. The correlation between total plasma MPA area under the concentration-time curve (AUC) or free plasma AUC and saliva MPA AUC was r2 = 0.25 and r2 = 0.13, respectively. The correlation between total plasma MPA AUC and total plasma MPA trough (C0) concentrations was r2 = 0.51, and between total plasma MPA AUC and saliva MPA trough concentrations, r2 = 0.03. Measurement of MPA concentration in saliva cannot currently replace plasma measurement for therapeutic drug monitoring of MPA following EC-MS administration. Additional studies are required to examine the relationship between MPA saliva concentrations and patient outcomes.

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.

Limited sampling strategy to predict mycophenolic acid area under the curve in pediatric patients with nephrotic syndrome: a retrospective cohort study

PurposeLimited sampling strategy (LSS) is a precise and relatively convenient therapeutic drug monitoring method. We evaluated LSSs for mycophenolic acid (MPA) in children with nephrotic syndrome treated with mycophenolic mofetil (MMF) and validated the LSSs using two different approaches.MethodsWe measured MPA plasma concentrations in 31 children using HPLC-UV method and received 37 MPA pharmacokinetic profiles (0–12 h). For six children, MPA profiles were estimated twice after two MMF doses. LSSs were developed using multilinear regression with STATISTICA and R software and validated using validation group and bootstrap method, respectively.ResultsThe best three time point equations included C1, C3, C6 (good guess 83%, bias − 2.78%; 95% confidence interval (CI) − 9.85–0.46); C1, C2, C6 (good guess 72%, bias 0.72%; 95% CI − 5.33–7.69); and C1, C2, C4 (good guess 72%, bias 2.05%; 95% CI − 4.92–13.01) for STATISTICA software. For R software, the best equations consisted of C1, C3, C6 (good guess 92%, bias − 2.69%; 95% CI − 27.18–33.75); C0, C1, C3 (good guess 84%, bias − 2.11%; 95% CI − 24.19–22.29); and C0, C1, C2 (good guess 84%, bias − 0.48%; 95% CI − 30.77–54.07). During validation, better results were obtained for R evaluations, i.e., bootstrap method.ConclusionsThe most useful equations included C0, C1, C3 and C0, C1, C2 time points; however, the most precise included C1, C3, C6 time points because of MPA enterohepatic recirculation. Better results were obtained for bootstrap validation due to greater number of patients. Validated LSS should be used only in the population for which it was developed. As there is growing evidence that underexposure of MPA is associated with insufficient treatment response, we recommend the introduction of therapeutic drug monitoring for MPA in children with nephrotic syndrome.

Regression and Genomic Analyses on the Association Between Dose-Normalized Mycophenolic Acid Exposure and Absolute Neutrophil Count in Steroid-Free, De Novo Kidney Transplant Recipients

The hematological side effects associated with mycophenolic acid (MPA) are relatively common and have severe consequences. The majority of literature data have not shown clear consistency in the MPA exposure-neutropenia relationship. We hypothesized that (i) adult de novo kidney transplant recipients who develop neutropenia have relatively higher dose-normalized MPA exposure than patients without neutropenia, and (ii) the observed neutropenia may be explained by polymorphisms in metabolism and/or transporter genes responsible for MPA disposition. Adult kidney transplant recipients on steady-state tacrolimus and MPA, not receiving a corticosteroid, and with stable renal function were recruited for investigation at three periods post-transplant (1, 3, and 12months; n = 21, 17, and 13, respectively). Clinical variables (age, weight, MPA daily dose, albumin, serum creatinine, absolute neutrophil count), tacrolimus and MPA concentrations (for exposure calculation), and genotypes (UGT2B7 G211T, UGT2B7 C802T, UGT1A9 T-275A, UGT1A9 T98C, MRP2 C-24T, MRP2 G1249A, OATP1B1 A388G, OATP1B1 C463A) were characterized. A significant inverse association between dose-normalized MPA exposure (a surrogate marker for apparent MPA clearance) and absolute neutrophil count in all three study periods (r2 ~ 0.3-0.7) was observed. No associations between characterized single nucleotide polymorphisms and MPA exposure or absolute neutrophil count were established. However, significant alterations in the minor allele frequencies of UGT2B7*2 C802T, UGT1A9 T275A, and MRP2 G1249A were evident. These findings support the clinical strategy for conducting MPA therapeutic drug monitoring in adult kidney transplant patients on steroid-free immunosuppressant therapy. The novel population genomic analysis data warrant further epidemiological investigations in a larger study sample.

Mycophenolic Acid Therapeutic Drug Monitoring in De Novo Renal Transplant Patients and the Related Outcomes

Mycophenolic Acid Therapeutic Drug Monitoring in De Novo Renal Transplant Patients and the Related Outcomes

Intra-individual variability of mycophenolic acid concentration according to renal function in liver transplant recipients receiving mycophenolate monotherapy.

Backgrounds/AimsMycophenolate mofetil (MMF) has wide inter- and intra-individual variability of mycophenolic acid (MPA) after liver transplantation (LT). On this study, we aimed to analyse the intra-individual variability of MPA concentration in stable adult LT recipients receiving MMF monotherapy and develop a method to determine the target level in the situation of wide intra-individual variability.MethodsThis retrospective cross-sectional study included 30 LT recipients. All patients received MMF monotherapy at a dose of 500 mg twice daily for ≥2 years and were divided into two groups based on renal function. MPA concentration-associated values were presented as mean with standard deviation and coefficient of variation (CV).ResultsThe normal renal function group (n=15) showed a mean 12-hour MPA concentration of 2.5±0.5 µg/ml (range, 1.8±0.5 to 3.6±0.7 µg/ml) and a mean CV of 20.4±7.7% (range, 8.7% to 39.4%). In the renal dysfunction group (n=15), the 12-hour MPA concentration fluctuated more widely with a mean value of 3.7±0.9 µg/ml (range, 2.8±0.8 to 5.1±1.2 µg/ml) and a mean CV of 24.5±4.9% (range, 17.1% to 37.5%). The 12-hour MPA concentration was significantly higher in the renal dysfunction group, as compared to the normal renal function group (p=0.001); whereas, the CV was not significantly different between the two groups (p=0.093).ConclusionsWe determined the inter- and intra-individual variability of 12-hour MPA concentration after LT. The results suggested that therapeutic drug monitoring of MPA is necessary due to the inter-individual and intra-individual variability of MMF pharmacokinetics, especially in LT recipients with renal dysfunction.