A Reliable Limited Sampling Strategy for the Estimation of Mycophenolic Acid Area Under the Concentration Time Curve in Adult Renal Transplant Patients in the Stable Posttransplant Period

External Validation of a Limited Sampling Strategy for the Estimation of Mycophenolic Acid Exposure Between Different Assay Methods: PETINIA and HPLC Methods

INTRODUCTION

A limited sampling strategy (LSS) for estimating the area under the plasma concentration-time curve (AUC0-12) of the immunosuppressant mycophenolic acid (MPA) is used for therapeutic drug monitoring (TDM) in clinical practice. Our study delves into the applicability of the MPA AUC0-12 LSS, originally developed using particle-enhanced turbidimetric inhibition immunoassay (PETINIA) measurements, to those obtained via high-performance liquid chromatography with ultraviolet detection (HPLC-UV).

METHODS

We developed an LSS for estimating MPA AUC0-12 based on PETINIA measurements in 32 adult kidney transplant patients who were receiving mycophenolate mofetil. Validation of this strategy was conducted in an additional 14 adult kidney transplant patients (validation sets) through measurements obtained by both PETINIA and HPLC-UV. Predictive performance was assessed using mean absolute error (MAE), root mean squared error (RMSE), and "good guess" defined as predicted AUC within observed AUC ± 15%.

RESULTS

The three time point equation (0, 2, and 6 h) emerged as optimal for estimating MPA AUC0-12, balancing predictive performance and usefulness in clinical settings. In validation sets, the coefficient of determination for observed versus predicted AUC0-12 was consistent between PETINIA (0.978) and HPLC-UV (0.958) measurements. Comparable MAE, RMSE, and "good guess" outcomes were observed for PETINIA (6.4%, 8.1%, and 85.7%, respectively) and HPLC-UV (7.6%, 9.4%, and 85.7%, respectively) measurements.

CONCLUSION

Our findings support the application of the MPA AUC0-12 LSS, originally developed using PETINIA measurements, to those obtained via HPLC-UV.

Population Pharmacokinetics and Limited Sampling Strategy of Mycophenolate Mofetil for Indian Patients With Lupus Nephritis

BACKGROUND

Mycophenolic acid is widely used to treat lupus nephritis (LN). However, it exhibits complex pharmacokinetics with large interindividual variability. This study aimed to develop a population pharmacokinetic (popPK) model and a 3-sample limited sampling strategy (LSS) to optimize therapeutic drug monitoring in Indian patients with LN.

METHODS

Five blood samples from each LN patient treated with mycophenolic acid were collected at steady-state predose and 1, 2, 4, and 6 hours postdose. Demographic parameters were tested as covariates to explain interindividual variability. PopPK analysis was performed using Monolix and the stochastic approximation expectation-maximization algorithm. An LSS was derived from 500 simulated pharmacokinetic (PK) profiles using maximum a posteriori Bayesian estimation to estimate individual PK parameters and area under the curve (AUC). The LSS-calculated AUC was compared with the AUC calculated using the trapezoidal rule and all the simulated samples.

RESULTS

A total of 51 patients were included in this study. Based on the 245 mycophenolic acid concentrations, a 1-compartmental model with double absorption using gamma distributions best fitted the data. None of the covariates improved the model significantly. The model was internally validated using diagnostic plots, prediction-corrected visual predictive checks, and bootstrapping. The best LSS included samples at 1, 2, and 4 hours postdose and exhibited good performances in an external dataset (root mean squared error, 21.9%; mean bias, -4.20%).

CONCLUSIONS

The popPK model developed in this study adequately estimated the PK of mycophenolic acid in adult Indian patients with LN. This simple LSS can optimize TDM based on the AUC in routine practice.

A Systematic Review of Multiple Linear Regression-Based Limited Sampling Strategies for Mycophenolic Acid Area Under the Concentration-Time Curve Estimation

Background and Objective

One approach of therapeutic drug monitoring in the case of mycophenolic acid (MPA) is a limited sampling strategy (LSS), which allows the evaluation of the area under the concentration–time curve (AUC) based on few concentrations. The aim of this systematic review was to review the MPA LSSs and define the most frequent time points for MPA determination in patients with different indications for mycophenolate mofetil (MMF) administration.

Methods

The literature was comprehensively searched in July 2021 using PubMed, Scopus, and Medline databases. Original articles determining multiple linear regression (MLR)-based LSSs for MPA and its free form (fMPA) were included. Studies on enteric-coated mycophenolic sodium, previously established LSS, Bayesian estimator, and different than twice a day dosing were excluded. Data were analyzed separately for (1) adult renal transplant recipients, (2) adults with other than renal transplantation indication, and (3) for pediatric patients.

Results

A total of 27, 17, and 11 studies were found for groups 1, 2, and 3, respectively, and 126 MLR-based LSS formulae (n = 120 for MPA, n = 6 for fMPA) were included in the review. Three time-point equations were the most frequent. Four MPA LSSs: 2.8401 + 5.7435 × C0 + 0.2655 × C0.5 + 1.1546 × C1 + 2.8971 × C4 for adult renal transplant recipients, 1.783 + 1.248 × C1 + 0.888 × C2 + 8.027 × C4 for adults after islet transplantation, 0.10 + 11.15 × C0 + 0.42 × C1 + 2.80 × C2 for adults after heart transplantation, and 8.217 + 3.163 × C0 + 0.994 × C1 + 1.334 × C2 + 4.183 × C4 for pediatric renal transplant recipients, plus one fMPA LSS, 34.2 + 1.12 × C1 + 1.29 × C2 + 2.28 × C4 + 3.95 × C6 for adult liver transplant recipients, seemed to be the most promising and should be validated in independent patient groups before introduction into clinical practice. The LSSs for pediatric patients were few and not fully characterized. There were only a few fMPA LSSs although fMPA is a pharmacologically active form of the drug.

Conclusions

The review includes updated MPA LSSs, e.g., for different MPA formulations (suspension, dispersible tablets), generic form, and intravenous administration for adult and pediatric patients, and emphasizes the need of individual therapeutic approaches according to MMF indication. Five MLR-based MPA LSSs might be implemented into clinical practice after evaluation in independent groups of patients. Further studies are required, e.g., to establish fMPA LSS in pediatric patients.

Post-transplant complications, patient, and graft survival in pediatric and adolescent kidney transplant recipients at a tropical tertiary care center across two immunosuppression eras

BACKGROUND

We report pediatric PAKT patient and graft outcomes at a large tropical tertiary center spanning two transplant eras.

METHODS

In this retrospective cohort study, all children ≤18 years who underwent kidney transplantation at our center between 1991 and 2016 were included. Data pertaining to their baseline characteristics, post-transplant events, and outcome were retrieved from transplant records and compared between transplant eras (1991-2005 and 2006-2016).

RESULTS

A total of 139 children (mean age 15.2 ± 2.9 years) underwent PAKT during this period. The incidence of UTIs, CMV disease, BKVN, invasive fungal infections, new-onset diabetes after transplant, leucopenia, and recurrent NKD was higher in the 2006-2016 era (P < .001 for all), while 1-year cumulative BPAR was comparable (P = .100). Five-year graft and patient survival in the two eras were 89.9% and 94.2% (P = .365) and 92.1% and 95.3% (P = .739), respectively. Incidence of CMV disease, BKVN, graft loss, and death was lower in the calcineurin withdrawal group. Non-adherence accounted for 36% of graft loss; infections caused 43.7% of deaths. On multivariate Cox proportional hazards analysis, independent predictors for graft loss were UTIs and blood transfusion naïve status and for death were serious infections and glomerular NKD.

CONCLUSIONS

PAKT in India has excellent long-term graft outcomes, though patient outcomes remain suboptimal owing to a high burden of infections. Current immunosuppression protocols need to be re-examined to balance infection risk, graft, and patient survival.

Pharmacokinetic Comparison of Two Mycophenolate Mofetil Formulations in Kidney Transplant Recipients

BACKGROUND

The aim of this study was to investigate and compare the pharmacokinetic (PK) characteristics of mycophenolate mofetil (MMF) capsule and MMF dispersible tablet by detecting the active metabolite of mycophenolic acid (MPA) in Chinese kidney transplant recipients.

METHODS

In the prospective, randomized, open-label study, the renal transplant patients were given a multiple dose of either the MMF capsule or MMF dispersible tablet combination with tacrolimus (Tac). For each patient, 11 serial blood samples were collected over 12 hours (h). Parameters including predose concentration (C0), postdose minimum and maximum concentration (Cmin and Cmax), time to Cmax (Tmax), total body clearance (CL), and area under the concentration-time curve for the 12-hour exposure (AUC0-12h) were determined. Patient interviews were conducted to assess the occurrence of adverse events.

RESULTS

Baseline characteristics were comparable between both groups. The C0, Cmin, Cmax, Tmax, CL, and AUC0-12h values were not significantly different after multiple doses of MMF capsule or MMF dispersible tablet (P > 0.05). The median values of AUC0-12h were 43.98 and 41.95 mcg·h/mL for MMF capsule and MMF dispersible tablet, respectively. Interindividual variability in Cmax, Cmin, and C0 were considerable in both groups. No serious adverse events were reported by patients or found on analysis of laboratory tests.

CONCLUSIONS

PK parameters of the 2 MPA drugs were comparable in early renal transplant patients in this study. The 2 formulations were well tolerated in Chinese kidney transplant patients.

Pharmacokinetics of Mycophenolate Mofetil and Development of Limited Sampling Strategy in Early Kidney Transplant Recipients

The mycophenolate mofetil (MMF) dose management for optimization of post-transplant treatment especially the early postoperative phase has been well recognized. MMF is a pro-drug of mycophenolic acid (MPA) and is widely used in Chinese renal transplant patients. Until now, the pharmacokinetic (PK) characteristics and model for the area under the concentration–time curve for the 12-h (h) of exposure (AUC_0-12h) of MPA (MPA-AUC_0-12h) estimation were lacking for the new formulation of MMF dispersible tablet in renal transplant patients. The aims of the study were to investigate the PK characteristics of MMF dispersible tablet by detecting the active metabolite of MPA and to establish an accuracy and precision equation for calculating MPA-AUC_0-12h by limited sampling strategy (LSS) in Chinese kidney transplant patients. A total of 60 postoperative kidney transplant recipients were given a multiple-dose of MMF dispersible tablet twice daily combination with tacrolimus (Tac) and steroids. On the 5th day post-transplantation, blood specimens were collected before drug administration and up to 12 h after MMF dispersible tablet administration. Non-compartmental PK analysis was used to determine the data obtained from individual patients. Multivariate stepwise regression analysis was used to develop models for predicting MPA-AUC_0-12h. The 3- and 4-point sampling models using 2 h, 4 h, 8 h and 1 h, 2 h, 4 h and 8 h, respectively, allowed accurate estimation of MPA-AUC_0-12h. PK parameters of MMF dispersible tablet were obtained and the 4-point LSS is the best model for accurate and precise estimation of MPA-AUC_0-12h.

Evaluation of Mycophenolate Mofetil and Low-Dose Steroid Combined Therapy in Moderately Severe Henoch-Schönlein Purpura Nephritis

Background

The most appropriate management of Henoch-Schönlein Purpura (HSP) nephritis with nephrotic-range proteinuria remains uncertain. The aim of this study was to evaluate the clinical therapeutic effects of mycophenolate mofetil and low-dose steroid in Henoch-Schönlein purpura nephritis (HSPN) with nephrotic-range proteinuria and pathological classification less than IV in children.

Material/Methods

The clinical effects of MMF and low-dose steroid therapy were studied in children with Henoch-Schönlein purpura nephritis manifested with nephrotic-range proteinuria, normal kidney function, and <50% crescents or sclerosing lesions on renal biopsy. We enrolled 32 boys and 29 girls with nephrotic-range proteinuria, normal kidney function, and pathological classification less than IV on renal biopsy. We treated 41 cases (67.2%) with mycophenolate mofetil and low-dose prednisone combined therapy and 20 cases (32.8%) were treated with full-dose prednisone alone.

Results

Short-term response was significantly different between 2 groups (χ²=4.371, P=0.037), while no significant difference was found in long-term prognosis (χ²=0.419, P=0.522) after follow-up. The ROC curve showed that the most appropriate cutoff value was 30.67 μg·h/ml for MPA-AUC and the area under the ROC curve was 0.731, with 85.2% sensitivity and 64.3% specificity.

Conclusions

Mycophenolate mofetil and low-dose prednisone combined therapy is a reasonable treatment choice which can promote the remission of proteinuria without increasing obvious adverse reactions in pediatric HSPN with nephrotic state and pathological classification less than grade IV. MPA-AUC more than 30 μg·h/ml was an appropriate value for MMF in the combined therapy with MMF and steroid for treating children with HSPN.

Development and validation of limited sampling strategy equation for mycophenolate mofetil in children with systemic lupus erythematosus

The aim of this study was to establish a limited sample strategy (LSS) to predict the mycophenolic acid (MPA) area under the curve (AUC)_(0-12) in children with systemic lupus erythematosus (SLE). Three months after initiation of mycophenolate mofetil (MMF) 26 children with SLE presented for therapeutic drug monitoring of MPA. On the day of the test, 10 specimens were collected, analyzed, and MPA AUC_(0-12) was calculated. Using step-wise regression analysis, LSS equations were developed. Using bootstrap validation, the predictive performance was calculated. The measured mean (standard deviation) for the trough concentration and AUC_(0-12) were 2.55 (1.57) μg/ml and 62.6 (21.67) mg.h/L, respectively. The range of trough concentrations and AUC_(0-12) were 0.7-5.54 μg/ml and 22.1-104.8 mg.h/L, respectively. The interindividual variability (%CV) for dose normalized AUC_(0-12) and dose normalized C_trough was 46.5% and 61.1%, respectively. The correlation between the concentrations at the different time points and MPA AUC_(0-12) ranged from 0.05 (1.5 h) to 0.56 (4 h). Two LSS equations that included 4 or 5 time points up to 3 h were developed and validated. The 4 point LSS had a correlation (R²) of 0.88 and the 5 point LSS an R² of 0.87. With respect to the 4 point and 5 point MPA LSS AUC_(0-12), the bias was 1.92% and 1.96%, respectively, and the imprecision was 11.24% and 11.28%, respectively. A 4 point LSS which concludes within 3 h after the administration of the MMF dose was developed and validated, to determine the MPA AUC_(0-12) in children with SLE.

How accurate and precise are limited sampling strategies in estimating exposure to mycophenolic acid in people with autoimmune disease?

Mycophenolic acid (MPA) is a potent immunosuppressant agent, which is increasingly being used in the treatment of patients with various autoimmune diseases. Dosing to achieve a specific target MPA area under the concentration-time curve from 0 to 12 h post-dose (AUC12) is likely to lead to better treatment outcomes in patients with autoimmune disease than a standard fixed-dose strategy. This review summarizes the available published data around concentration monitoring strategies for MPA in patients with autoimmune disease and examines the accuracy and precision of methods reported to date using limited concentration-time points to estimate MPA AUC12. A total of 13 studies were identified that assessed the correlation between single time points and MPA AUC12 and/or examined the predictive performance of limited sampling strategies in estimating MPA AUC12. The majority of studies investigated mycophenolate mofetil (MMF) rather than the enteric-coated mycophenolate sodium (EC-MPS) formulation of MPA. Correlations between MPA trough concentrations and MPA AUC12 estimated by full concentration-time profiling ranged from 0.13 to 0.94 across ten studies, with the highest associations (r (2) = 0.90-0.94) observed in lupus nephritis patients. Correlations were generally higher in autoimmune disease patients compared with renal allograft recipients and higher after MMF compared with EC-MPS intake. Four studies investigated use of a limited sampling strategy to predict MPA AUC12 determined by full concentration-time profiling. Three studies used a limited sampling strategy consisting of a maximum combination of three sampling time points with the latest sample drawn 3-6 h after MMF intake, whereas the remaining study tested all combinations of sampling times. MPA AUC12 was best predicted when three samples were taken at pre-dose and at 1 and 3 h post-dose with a mean bias and imprecision of 0.8 and 22.6 % for multiple linear regression analysis and of -5.5 and 23.0 % for maximum a posteriori (MAP) Bayesian analysis. Although mean bias was less when data were analysed using multiple linear regression, MAP Bayesian analysis is preferable because of its flexibility with respect to sample timing. Estimation of MPA AUC12 following EC-MPS administration using a limited sampling strategy with samples drawn within 3 h post-dose resulted in biased and imprecise results, likely due to a longer time to reach a peak MPA concentration (t max) with this formulation and more variable pharmacokinetic profiles. Inclusion of later sampling time points that capture enterohepatic recirculation and t max improved the predictive performance of strategies to predict EC-MPS exposure. Given the considerable pharmacokinetic variability associated with mycophenolate therapy, limited sampling strategies may potentially help in individualizing patient dosing. However, a compromise needs to be made between the predictive performance of the strategy and its clinical feasibility. An opportunity exists to combine research efforts globally to create an open-source database for MPA (AUC, concentrations and outcomes) that can be used and prospectively evaluated for AUC target-controlled dosing of MPA in autoimmune diseases.

A Protocol for the Pharmacokinetics of Enteric Coated Mycophenolate Sodium in Lupus Nephritis (POEMSLUN): an open-label, randomised controlled trial

INTRODUCTION

Mycophenolate sodium, an enteric-coated tablet (EC-MPS), is as effective and safe as mycophenolate mofetil (MMF) in preventing transplant rejection. EC-MPS and MMF improve the outcome of severe lupus nephritis (LN) and have fewer side effects than pulsed intravenous cyclophosphamide. Blood concentrations of mycophenolic acid (MPA), the active metabolite of EC-MPS, vary between participants despite fixed dosing. Interpatient variability has been studied in transplantation, but not well documented in LN. The relationship between MPA concentration and its clinical effect on LN has not been described.

METHODS AND ANALYSIS

This is a prospective, open-label, randomised controlled trial. -32 participants with LN who meet the inclusion and exclusion criteria will be randomised into two groups: one receiving a fixed dose of EC-MPS and the second, a dosing regimen that is titrated with therapeutic drug monitoring. Included participants will have blood sampled over a period of 8-12 h on three different occasions. Pharmacokinetic parameters will be calculated using non-compartmental methods.

ETHICS AND DISSEMINATION

The Human Research and Ethics Committee of the Royal Brisbane Women's Hospital have approved this study. The study is registered with Australian and New Zealand Clinical Trials Registry-ACTRN12611000798965 We planned to present the de-identified information at conferences and publish the results in medical journals.

TRIAL REGISTRATION

ACTRN12611000798965.

Limited sampling strategy of mycophenolic acid in adult kidney transplant recipients: influence of the post-transplant period and the pharmacokinetic profile

We aimed to develop an accurate and convenient LSS for predicting MPA-AUC(0-12 hours) in Tunisian adult kidney transplant recipients whose immunosuppressive regimen consisted of MMF and tacrolimus combination with regards to the post-transplant period and the pharmacokinetic profile. Each pharmacokinetic profile consisted of eight blood samples collected during the 12-hour dosing interval. The AUC(0-12 hours) was calculated according to the linear trapezoidal rule. The MPA concentrations at each sampling time were correlated by a linear regression analysis with the measured AUC(0-12). We analyzed all the developed models for their ability to estimate the MPA-AUC(0-12 hours). The best multilinear regression model for predicting the full MPA-AUC(0-12 hours) was found to be the combination of C1, C4, and C6. All the best correlated models and the most convenient ones were verified to be also applicable before 5 months after transplantation and thereafter. These models were also verified to be applicable for patients having or not the second peak in their pharmacokinetic profiles. For practical reasons we recommend a LSS using C0, C1, and C4 that provides a reasonable MPA-AUC(0-12 hours) estimation.

Omeprazole limited sampling strategies to predict area under the concentration-time curve ratios: implications for cytochrome P450 2C19 and 3A phenotyping

PURPOSE

To develop a limited sampling strategy (LSS) to predict area under the concentration-time curve (AUC) ratios of omeprazole (AUC(OPZ)) to its metabolites 5-hydroxyomeprazole (AUC(5OH)) and omeprazole sulfone (AUC(SUL)) as phenotyping parameters for cytochrome P450 (CYP) 2C19 and 3A.

METHODS

Data were obtained from 37 (4 women) Caucasian, Chinese, and Korean healthy adults from three published studies. The AUC(OPZ), AUC(5OH), and AUC(SUL) were calculated via noncompartmental analysis. Observed AUC(OPZ, OBS)/AUC(5OH, OBS) and AUC(OPZ, OBS)/AUC(SUL, OBS) were determined. Plasma concentrations of omeprazole, 5-hydroxyomeprazole, and omeprazole sulfone at 1, 1.5, 2, 3, 4, 6, and 8 h post-dose were used to generate limited sampling strategy (LSS) models to predict AUC(OPZ,PRE)/AUC(5OH,PRE) and AUC(OPZ,PRE/)AUC(SUL,PRE). Bias and precision were assessed via percentage mean prediction error (%MPE) and percentage mean absolute error (%MAE), with acceptable limits being <15%.

RESULTS

For CYP2C19, the AUC(OPZ,OBS)/AUC(5OH,OBS) was [mean ± standard deviation (SD)] 2.10 ± 1.63. Five LSS models of AUC(OPZ,PRE)/AUC(5OH,PRE) were generated, but none met the bias or precision criteria. Upon stratification by CYP2C19 genotype and ethnicity, a three-timepoint (at 1, 2, and 4 h) LSS model accurately predicted AUC(OPZ)/AUC(5OH) in Caucasian CYP2C19*1/*1 subjects. For CYP3A, AUC(OPZ,OBS)/AUC(SUL,OBS) (mean ± SD) was 1.79 ± 0.67. All LSS models had unacceptable %MAE, even when stratified by CYP2C19 genotype and ethnicity.

CONCLUSIONS

A LSS model to predict AUC(OPZ)/AUC(5OH), and thus CYP2C19 activity, was generated for Caucasian CYP2C19*1/*1 subjects. However, additional model validation is needed prior to general use. LSS models to predict AUC(OPZ)/AUC(SUL), and thus CYP3A activity, were not possible, even upon stratification by CYP2C19 genotype and ethnicity.

A possible simplification for the estimation of area under the curve (AUC₀₋₁₂) of enteric-coated mycophenolate sodium in renal transplant patients receiving tacrolimus

Enteric-coated mycophenolate sodium (EC-MPS) is widely used in renal transplantation. With a delayed absorption profile, it has not been possible to develop limited sampling strategies to estimate area under the curve (mycophenolic acid [MPA] AUC₀₋₁₂), which have limited time points and are completed in 2 hours. We developed and validated simplified strategies to estimate MPA AUC₀₋₁₂ in an Indian renal transplant population prescribed EC-MPS together with prednisolone and tacrolimus. Intensive pharmacokinetic sampling (17 samples each) was performed in 18 patients to measure MPA AUC₀₋₁₂. The profiles at 1 month were used to develop the simplified strategies and those at 5.5 months used for validation. We followed two approaches. In one, the AUC was calculated using the trapezoidal rule with fewer time points followed by an extrapolation. In the second approach, by stepwise multiple regression analysis, models with different time points were identified and linear regression analysis performed. Using the trapezoidal rule, two equations were developed with six time points and sampling to 6 or 8 hours (8hrAUC[₀₋₁₂exp]) after the EC-MPS dose. On validation, the 8hrAUC(₀₋₁₂exp) compared with total measured AUC₀₋₁₂ had a coefficient of correlation (r²) of 0.872 with a bias and precision (95% confidence interval) of 0.54% (-6.07-7.15) and 9.73% (5.37-14.09), respectively. Second, limited sampling strategies were developed with four, five, six, seven, and eight time points and completion within 2 hours, 4 hours, 6 hours, and 8 hours after the EC-MPS dose. On validation, six, seven, and eight time point equations, all with sampling to 8 hours, had an acceptable r with the total measured MPA AUC₀₋₁₂ (0.817-0.927). In the six, seven, and eight time points, the bias (95% confidence interval) was 3.00% (-4.59 to 10.59), 0.29% (-5.4 to 5.97), and -0.72% (-5.34 to 3.89) and the precision (95% confidence interval) was 10.59% (5.06-16.13), 8.33% (4.55-12.1), and 6.92% (3.94-9.90), respectively. Of the eight simplified approaches, inclusion of seven or eight time points improved the accuracy of the predicted AUC compared with the actual and can be advocated based on the priority of the user.