Total and free mycophenolic acid and its 7-O-glucuronide metabolite in Chinese adult renal transplant patients: pharmacokinetics and application of limited sampling strategies

Limited sampling strategy to predict free mycophenolic acid area under the concentration-time curve in paediatric patients with nephrotic syndrome

In paediatric patients, there is no data on the recommended area under the concentration-time curve from 0 to 12 h (AUC_0-12 ) for free mycophenolic acid (fMPA), which is the active form of the drug, responsible for the pharmacological effect. We decided to establish the limited sampling strategy (LSS) for fMPA for its use in MPA therapeutic monitoring in children with nephrotic syndrome treated with mycophenolate mofetil (MMF). This study included 23 children (aged 11 ± 4 years) from whom eight blood samples were collected within 12 h after MMF administration. The fMPA was determined using the high-performance liquid chromatography with fluorescence detection method. LSSs were estimated with the use of R software and bootstrap procedure. The best model was chosen based on a number of profiles with AUC predicted within ± 20% of AUC_0-12 (good guess), r² , mean prediction error (%MPE) of ±10% and mean absolute error (%MAE) of less than 25%. The fMPA AUC_0-12 was 0.1669 ± 0.0697 μg h/mL and the free fraction was within 0.16%-0.81%. In total, there were 92 equations developed of which five fulfilled the acceptance criteria for %MPE, %MAE, good guess >80% and r²  > 0.900. These equations consisted of three time points: model 1 (C₁ , C₂ , C₆ ), model 2 (C₁ , C₃ , C₆ ), model 3 (C₁ , C₄ , C₆ ), model 5 (C₀ , C₁ , C₂ ), and model 6 (C₁ , C₂ , C₉ ). Although blood sampling up to 9 h after MMF dosing is impractical, it is crucial to include C₆ or C₉ in LSS to assess fMPA AUC_pred correctly. The most practical fMPA LSS, which fulfilled the acceptance criteria in the estimation group, was fMPA AUC_pred  = 0.040 + 2.220 × C₀  + 1.130 × C₁  + 1.742 × C₂ . Further studies should define the recommended fMPA AUC_0-12 value in children with nephrotic syndrome.

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.

Effect of Meal Timings and Meal Content on the AUC0-12h of Mycophenolic Acid: A Simulation Study

Meal timings and content related to gallbladder emptying in the enterohepatic circulation are important for explaining the high variability in mycophenolic acid exposure. The limited sampling strategy (LSS) was established to estimate the area under the plasma concentration-time curve from time 0 to 12 hours (AUC_0-12h ) of mycophenolic acid in therapeutic drug monitoring. The aim of this study is to investigate the effect of meal timings and content on the AUC_0-12h of mycophenolic acid and to assess the influence of meals on LSS. A mycophenolic acid pharmacokinetic model with a mechanism-based enterohepatic circulation process was employed to perform simulations under various assumed meal scenarios. The simulations were compared to evaluate the effect of meal timings and meal content on mycophenolic acid AUC_0-12h . Monte Carlo simulations were performed using the meal parameter with the greatest impact on mycophenolic acid AUC_0-12h as a variable. The corresponding LSS equations were established, and the predictive performance was assessed. Both the meal timings and meal content affected the mycophenolic acid AUC_0-12h , and the postdose fasting period had the greatest impact. The predictive performance of the LSS is sensitive to the postdose fasting period. Therefore, meal timings may improve the estimation of mycophenolic acid AUC_0-12h and the efficacy of therapeutic drug monitoring.

Significant Correlations between p-Cresol Sulfate and Mycophenolic Acid Plasma Concentrations in Adult Kidney Transplant Recipients

BACKGROUND AND OBJECTIVES

Mycophenolic acid (MPA) is a commonly prescribed life-long immunosuppressant for kidney transplant recipients. The frequently observed large variations in MPA plasma exposure may lead to severe adverse outcomes; therefore, characterizations of contributing factors can potentially improve the precision dosing of MPA. Our group recently reported the potent inhibitory effects of p-cresol (a protein-bound uremic toxin that can be accumulated in kidney transplant patients) on the hepatic metabolism of MPA in human in vitro models. Based on these data, the hypothesis for this clinical investigation was that a direct correlation between p-cresol and MPA plasma exposure should be evident in adult kidney transplant recipients.

METHODS

Using a prospective and observational approach, adult kidney transplant recipients within the first year after transplant on oral mycophenolate mofetil (with tacrolimus ± prednisone) were screened for recruitment. The exclusion criteria were cold ischemia time > 30 h, malignancy, pregnancy, severe renal dysfunction (i.e., estimated glomerular filtration rate, eGFR, < 10 mL/min/1.73 m²), active graft rejection, or MPA intolerance. Patients' demographic and biochemistry data were collected. Total and free plasma concentrations of MPA, MPA glucuronide (MPAG), and total p-cresol sulfate (the predominant, quantifiable form of p-cresol in the plasma) were quantified using validated assays. Correlational and categorical analyses were performed using GraphPad Prism.

RESULTS

Forty patients (11 females) were included: donor type (living/deceased: 20/20), induction regimen (basiliximab/thymoglobulin/basiliximab followed by thymoglobulin: 35/3/2), post-transplant time (74 ± 60 days, mean ± standard deviation), age (53.7 ± 12.4 years), bodyweight (79.8 ± 18.5 kg), eGFR (51.9 ± 18.0 mL/min/1.73 m²), serum albumin (3.6 ± 0.5 g/dL), prednisone dose (18.5 ± 13.2 mg, n = 33), and tacrolimus trough concentration (9.4 ± 2.4 µg/L). Based on Spearman analysis, significant control correlations supporting the validity of our dataset were observed between total MPA trough concentration (C₀) and total MPAG C₀ (correlation coefficient [R] = 0.39), ratio of total MPAG C₀-to-total MPA C₀ and post-transplant time (R = - 0.56), total MPAG C₀ and eGFR (R = - 0.35), and p-cresol sulfate concentration and eGFR (R = - 0.70). Our primary analysis indicated the novel observation that total MPA C₀ (R = 0.39), daily dose-normalized total MPA C₀ (R = 0.32), and bodyweight-normalized total MPA C₀ (R = 0.32) were significantly correlated with plasma p-cresol sulfate concentrations. Consistently, patients categorized with elevated p-cresol sulfate concentrations (i.e., ≥ median of 3.2 µg/mL) also exhibited increased total MPA C₀ (by 57 % vs those below median), daily dose-normalized total MPA C₀ (by 89 %), and bodyweight-normalized total MPA C₀ (by 62 %). Our secondary analyses with MPA metabolites, unbound concentrations, free fractions, and MPA metabolite ratios supported additional potential interacting mechanisms.

CONCLUSION

We have identified a novel, positive association between p-cresol sulfate exposure and total MPA C₀ in adult kidney transplant recipients, which is supported by published mechanistic in vitro data. Our findings confirm a potential role of p-cresol as a significant clinical variable affecting the pharmacokinetics of MPA. These data also provide the justifications for conducting subsequent full-scale pharmacokinetic-pharmacodynamic studies to further characterize the cause-effect relationships of this interaction, which could also rule out potential confounding variables not adequately controlled in this correlational study.

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.

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.

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 (AUC_pred) in 24 children with nephrotic syndrome, for whom we previously determined MPA and fMPA concentrations, and compare the results with the determined AUC (AUC_total). 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.

Limited Sampling Strategy for Estimation of Mycophenolic Acid Exposure in Adult Chinese Heart Transplant Recipients

Background: With the increasing use of mycophenolic acid (MPA) formulations in organ transplantation, the need for personalized immunosuppressive therapy has become well recognized based on therapeutic drug monitoring (TDM) for avoidance of drug-related toxicity while maintaining efficacy. Few studies have assessed area under the 12 h concentration-time curve of MPA (MPA-AUC_0–12h) in heart transplant recipients who received mycophenolate mofetil (MMF) dispersible tablets (MMFdt). The aim of the study was to investigate the pharmacokinetics (PK) of MMFdt combined with tacrolimus and further to develop a practical method for estimation of MPA-AUC_0–12h using a limited sampling strategy (LSS).

Methods: A prospective study in a single center was performed in patients who continuously administrated with MMFdt or MMF capsule (MMFc) for at least 7 days after cardiac transplantation from 2018 to 2020. A total of 48 Chinese adult heart transplant recipients were enrolled. Blood samples were collected before and 0.5, 1, 1.5, 2, 4, 6, 8, 10 and 12 h after MMF administration. The validated high-performance liquid chromatography combined with tandem mass spectrometry method was used to measure MPA concentrations. Non-compartmental pharmacokinetic (PK) analysis was applied to calculate the data obtained from individual recipients by WinNonlin. LSS models were developed for MPA-AUC_0–12h prediction with multivariate stepwise regression analysis.

Results: A large inter-individual variability was observed in AUC_0–12h, T_max, C_max, MRT_0–12h, t_1/2 and CL/F after multiple dosing of MMFdt. However, no significant differences were observed between main PK parameters of MMFdt and MMFc. The best estimation of MPA-AUC_0–12h was achieved with four points: MPA-AUC_0–12h = 8.424 + 0.781 × C_0.5 + 1.263 × C₂ + 1.660 × C₄ + 3.022 × C₆ (R² = 0.844). The mean prediction error (MPE) and mean absolute prediction error (MAPE) of MPA-AUC_0–12h were 2.09 ± 14.05% and 11.17 ± 8.52%, respectively. Both internal and external validations showed good applicability for four-point LSS equation.

Conclusion: The results provide strong evidence for the use of LSS model other than a single time-point concentration of MPA when performing TDM. A four-point LSS equation using the concentrations at 0.5, 2, 4, 6 h is recommended to estimate MPA-AUC_0–12h during early period after transplantation in Chinese adult heart transplant recipients receiving MMFdt or MMFc. However, proper internal and external validations with more patients should be conducted in the future.

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

OBJECTIVES

The population pharmacokinetic (popPK) characteristics of total mycophenolic acid (tMPA) have been investigated in various ethnic populations. However, investigations of popPK of unbound MPA (uMPA) are few. Thus, a popPK analysis was performed to: (1) characterize the PK of uMPA and tMPA and its 7-O-mycophenolic acid glucuronide (MPAG) metabolite in kidney transplant patients cotreated with cyclosporine (CsA), and (2) identify the clinically significant covariates that explain variability in the dose-exposure relationship.

METHODS

A total of 740 uMPA, 741 tMPA, and 734 total MPAG (tMPAG) concentration-time data from 58 Chinese kidney transplant patients receiving MPA in combination with CsA were analyzed using NONMEM® software with the stochastic approximation expectation maximization (SAEM) followed by the important sampling (IMP) method. The influence of covariates was tested using a stepwise procedure.

RESULTS

The PK of uMPA and unbound MPAG (uMPAG) were characterized by a two- and one-compartment model with first-order elimination, respectively. A linear protein binding model was used to link uMPA and tMPA. Apparent clearance (CL/F) and central volume of distribution (VC/F) of uMPA (CLuMPA/F and VCuMPA/F, respectively) and protein binding rate constant (k B) were estimated to be 851 L/h [relative standard error (RSE), 7.1%], 718 L (18.5%) and 53.4/h (2.3%), respectively. For uMPAG, the population values (RSE) of CL/F (CLuMPAG) and VC/F (VCuMPAG/F) were 5.71 L/h (4.4%) and 29.9 L (7.7%), respectively. Between-subject variability (BSVs) on CLuMPA/F, VCuMPA/F, CLuMPAG/F, and VCuMPAG/F were 51.0, 80.0, 31.8 and 48.4%, respectively, whereas residual unexplained variability (RUVs) for uMPA, tMPA, and uMPAG were 47.0, 45.9, and 22.0%, respectively. Significant relationships were found between k B and serum albumin (ALB) and between CLuMPAG/F and glomerular filtration rate (GFR). Additionally, model-based simulation showed that changes in ALB concentrations substantially affected tMPA but not uMPA exposure.

CONCLUSIONS

The established model adequately described the popPK characteristics of the uMPA, tMPA, and MPAG. The estimated CLuMPA/F and unbound fraction of MPA (FUMPA) in Chinese kidney transplant recipients cotreated with CsA were comparable to those published previously in Caucasians. We recommend monitoring uMPA instead of tMPA to optimize mycophenolate mofetil (MMF) dosing for patients with lower ALB levels.

Optimization and application of an HPLC method for quantification of inosine-5'-monophosphate dehydrogenase activity as a pharmacodynamic biomarker of mycophenolic acid in Chinese renal transplant patients

BACKGROUND

The immunosuppressive agent mycophenolic acid (MPA) is a non-competitive, reversible inhibitor of inosine-5'-monophosphate dehydrogenase (IMPDH). Thus, IMPDH activity can serve as a potential pharmacodynamic biomarker to optimize dosing of MPA.

METHODS

Peripheral blood mononuclear cells were isolated from 2 mL blood samples and an in vitro enzymatic reaction was subsequently performed for 120 min. To determine IMPDH activity in Chinese healthy volunteers and renal transplant patients, a high performance liquid chromatography assay was established and validated by subtracting adenosine monophosphate (AMP) from blank samples for eliminating exogenous AMP interference.

RESULTS

The accuracy of our method ranged between -0.8% and 12.5%, and the precision ranged between 0.7% and 6.3%. The mean value of IMPDH activity across 11 healthy volunteers was 46.60 ± 14.28 μmol/s/mol AMP. A negative relationship between MPA concentration and IMPDH activity was observed in four renal transplant patients treated with MPA 13 days post-transplantation, while the inhibitory rate of IMPDH activity ranged from 24% to 42%.

CONCLUSION

A bioanalytical assay for IMPDH quantification was optimized and evaluated. The differences in the pharmacodynamics of MPA between Asians and Caucasians may provide some evidence for dosing differences among ethnicities.

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.

Population pharmacokinetics of mycophenolic acid and its main glucuronide metabolite: a comparison between healthy Chinese and Caucasian subjects receiving mycophenolate mofetil

PURPOSE

Mycophenolate mofetil (MMF), a prodrug of the immunosuppressive agent mycophenolic acid (MPA), is widely used for prophylaxis of solid organ transplant rejection. MPA is primarily metabolized to 7-O-mycophenolic acid glucuronide (MPAG), an inactive metabolite that undergoes enterohepatic recirculation (EHC). This study assessed ethnic differences in the pharmacokinetics (PK) of MPA and MPAG between healthy Chinese and Caucasian subjects using population PK analysis.

METHODS

Data were pooled from 132 healthy subjects (80 Chinese, 52 Caucasians) in eight clinical studies in which MMF was administered in a single oral dose. Population PK analysis was performed using NONMEM®.

RESULTS

The PK of MPA and MPAG were best described by a five-chain compartment model, including a gallbladder compartment for EHC and a transit absorption model. Ethnicity was significantly correlated with the apparent clearance (CL/F) and volume of distribution (V/F) of MPAG but not those of MPA. Weight was identified as a covariate and was correlated with the PK of MPA and MPAG. MPA CL/F was 11.5 L/h for a 70-kg healthy subject, and the MPAG CL/F values were 1.36 and 1.90 L/h for 70-kg Chinese and Caucasian individuals, respectively. Internal and external evaluation indicated model validity.

CONCLUSIONS

This is the first population PK analysis to evaluate ethnic differences in the PK of MPA and MPAG in healthy Chinese and Caucasian subjects. No differences were observed in the PK of MPA between healthy Chinese and Caucasian subjects. Although, the MPAG CL/F was approximately 40 % higher in Caucasians, this finding may not be clinically relevant.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Pharmacokinetics of free mycophenolic acid and limited sampling strategy for the estimation of area under the curve in liver transplant patients

Mycophenolate Mofetil (MMF) is widely used in preventing acute rejection in liver transplantation. Only free MPA (fMPA) can exert the pharmacological effect. In this study, we aimed to develop the new model which could be best fit to predict the fMPA area under the plasma concentration-time curve (AUC) by limited sampling strategy (LSS) in Chinese liver transplant patients. Fifty patients received MMF with the combination of tacrolimus. Free MPA concentrations were determined around day 7. Optimal subset regression analysis was used to establish the models for estimated fMPA AUC(0-12h). Three excellent better models were validated by Bootstrap analysis. Twenty-four models including four blood time point samplings were established. For the selected four models, 100% were successful and were not significantly different from the original dataset by Bootstrap analysis. The best model for prediction of fMPA AUC(0-12h) was by using C(1h), C(2h), C(4h) and C(6h). This model showed the minimal mean prediction error and the minimal mean absolute prediction error. In conclusion, the models for estimation of the fMPA AUC(0-12h) were established in liver transplant recipients and the best model for prediction of fMPA AUC was: estimated fMPA AUC=34.2+1.12C(1h)+1.29C(2h)+2.28C(4h)+3.95C(6h).

Limited sampling strategy models for estimating the AUC of gliclazide in Chinese healthy volunteers

The aim of this work is to reduce the cost of required sampling for the estimation of the area under the gliclazide plasma concentration versus time curve within 60 h (AUC0-60t ). The limited sampling strategy (LSS) models were established and validated by the multiple regression model within 4 or fewer gliclazide concentration values. Absolute prediction error (APE), root of mean square error (RMSE) and visual prediction check were used as criterion. The results of Jack-Knife validation showed that 10 (25.0 %) of the 40 LSS based on the regression analysis were not within an APE of 15 % using one concentration-time point. 90.2, 91.5 and 92.4 % of the 40 LSS models were capable of prediction using 2, 3 and 4 points, respectively. Limited sampling strategies were developed and validated for estimating AUC0-60t of gliclazide. This study indicates that the implementation of an 80 mg dosage regimen enabled accurate predictions of AUC0-60t by the LSS model. This study shows that 12, 6, 4, 2 h after administration are the key sampling times. The combination of (12, 2 h), (12, 8, 2 h) or (12, 8, 4, 2 h) can be chosen as sampling hours for predicting AUC0-60t in practical application according to requirement.

Cyclosporine alters correlation between free and total mycophenolic acid in kidney transplant recipients in the initial phase

WHAT IS KNOWN AND OBJECTIVE

The factors affecting the pharmacokinetics of free mycophenolic acid (MPA) and its phenolic glucuronide (MPAG) are still unclear. The aim of this study was to evaluate the influence of cyclosporine on the pharmacokinetics of free MPA and MPAG.

METHODS

Seventy-seven kidney transplant recipients (23 were in an initial phase and 54 in a stable phase; 41 were treated with cyclosporine and 36 with tacrolimus) were enrolled. Free and total MPA and MPAG were determined using HPLC. The correlations between free and total predose concentrations (C(0) ) of MPA or MPAG were evaluated separately in patients receiving calcineurin inhibitor medications.

RESULTS AND DISCUSSION

Serum concentration of albumin was lower in the initial phase than in the stable phase. A higher ratio of free MPAG C(0) to free MPA C(0) was observed in cyclosporine-treated than tacrolimus-treated kidney transplant recipients. Free MPA C(0) correlated weakly with total MPA C(0) in kidney transplant recipients treated with cyclosporine in the initial phase (ρ= 0·53, P = 0·06).

WHAT IS NEW AND CONCLUSION

Cyclosporine increased the ratio of free MPAG C(0) to free MPA C(0) and varied the free fraction of MPA in the hypoalbuminaemic kidney transplant recipients in the initial phase.

Development and validation of limited sampling strategies for tacrolimus and mycophenolate in steroid-free renal transplant regimens

PURPOSE

1) To develop and validate limited sampling strategies (LSSs) for tacrolimus (TAC) and mycophenolic acid (MPA) in renal transplant recipients not receiving corticosteroids; and 2) to evaluate predictive performance of published LSSs (for steroid-based regimens) in a steroid-free population.

METHODS

On administration of steady-state morning TAC and mycophenolate mofetil doses, 12-hour serial blood samples from 28 stable renal transplant recipients were collected and measured by validated high-performance liquid chromatography methods and area under the curve (AUC) by trapezoidal rule. TAC LSSs were developed and validated by multiple regression analysis by a two-group method (index n = 18; validation n = 10) and MPA LSSs by the jackknife method (n = 28). Potential LSSs were those with r ≥ .8 (TAC) or r ≥ 0.7 (MPA) and < 3 time points within 2 hours (TAC) or 4 hours (MPA) postdose. Predictive performance was calculated and other published TAC and MPA LSSs tested using preset criteria for bias and precision of within ± 15%.

RESULTS

For TAC, three three-concentration, one two-concentration, and one one-concentration model met preset criteria. The best equations were: TAC AUC = 10.338 + 7.739C0 + 3.589C2 (r = 0.956, bias = -3.4%, precision = 4.7%) and TAC AUC = 29.479 + 5.016C2 (r = 0.862, bias = 3.2%, precision = 9.7%). For MPA, only one model was identified: MPA AUC = 9.328 + 1.311C1 + 1.455C2 + 2.901C4 (r = 0.838, bias = -3.8%, precision = 14.9%). One published TAC (and no MPA) LSS in renal transplant recipients on steroid-based regimens met criteria.

CONCLUSIONS

To the authors' knowledge, these LSSs are the first to be developed and validated in steroid-free renal transplant recipients and can be used to accurately predict TAC and MPA AUCs for steroid-free regimens. Because the commonly used MPA LSS is based on a steroid regimen and not predictive for steroid-free patients, the newly derived MPA LSS is being applied at the authors' institution. Other renal transplant centers may also wish to validate this equation in their own patients.

Establishment of high-performance liquid chromatography and enzyme multiplied immunoassay technology methods for determination of free mycophenolic acid and its application in Chinese liver transplant recipients

The objective of this study is to investigate the correlation between methods of high-performance liquid chromatography (HPLC) and enzyme multiplied immunoassay technology (EMIT) for determination of total mycophenolic acid (tMPA) and free (fMPA) concentration and to study pharmacokinetics of fMPA in Chinese liver transplant recipients. An HPLC method with fluorometric detection and an EMIT assay were established to determine fMPA in plasma ultrafiltrates. Pharmacokinetic parameters of tMPA and fMPA in 51 patients were estimated. The calibration range of fMPA was 0.0025 to 1.0 μg/mL for the HPLC method and 0.0050 to 0.50 μg/mL for the EMIT method. Mean recovery of the two methods was 98.0% and 97.1%, respectively. The intraday and interday coefficient of variations were 0.93% to 3.1% and 1.6% to 2.9% for HPLC and 4.51% to 15.8% and 5.83% to 19.5% for EMIT, respectively. The relationship of the two methods was EMIT = 1.074 × HPLC + 0.582 (r2 = 0.918, n = 470, P < 0.05) for tMPA and EMIT = 1.068 × HPLC + 0.004 (r2 = 0.945, n = 297, P < 0.05) for fMPA. There was a positive mean bias of EMIT for tMPA (27.0%) and fMPA (23.3%). The AUC0-12 of tMPA and fMPA obtained by HPLC in 51 patients was 34.7 ± 11.1 and 0.72 ± 0.38 μg·h/mL, respectively. The free fraction of MPA was 1.60 ± 1.21% (Median:1.36%, interquartile: 0.72, 2.22), [corrected] which was significantly correlated with 7-O-glucuronide conjugate of MPA AUC0-12 (r2 = 0.705, P < 0.001), albumin (r2 = -0.529, P < 0.001), and the clearance of creatinine (r2 = -0.417, r2 = 0.005). Both HPLC and EMIT assay are suitable for the determination of fMPA. A considerable interindividual variability exists in pharmacokinetics of fMPA among Chinese liver transplant recipients. 7-O-Glucuronide conjugate of MPA and albumin concentrations are two factors correlated to fMPA variance.

Bioequivalence and pharmacokinetic comparison of two mycophenolate mofetil formulations in healthy Chinese male volunteers: an open-label, randomized-sequence, single-dose, two-way crossover study

BACKGROUND

Mycophenolate mofetil (MMF) is an ester prodrug of mycophenolic acid (MPA), so clinical studies measure the circulating plasma MPA concentration instead of MMF. MPA is extensively glucuronidated by several uridine diphosphate glycosyltransferases into an inactive 7-O-glucuronide and a pharmacologically active acylglucuronide. Considering the effect of racial differences and genetic factors on the pharmacokinetic (PK) properties of drugs, it is necessary to study them in Chinese populations.

OBJECTIVES

The aim of this study was to compare the clinical bioequivalence and PK properties of a test (dispersible tablets) and reference (capsules) formulation of MMF 1.0 g in healthy Chinese volunteers. We also established a validated HPLC method for the determination and quantification of MPA in human plasma. The study was required to obtain Chinese regulatory approval for the test formulation.

METHODS

This open-label, randomized-sequence, single-dose, 2-way crossover study was conducted at the First Hospital of Nanjing Medical University, Nanjing, China. Eligible subjects were healthy male volunteers who were randomly assigned at a 1:1 ratio to receive a single 1.0-g dose of the test or reference formulation, followed by a 1-week washout period and administration of the alternate formulation. The plasma concentration of MPA, which is the active metabolite of MMF, was determined using a validated HPLC method. For analysis of PK properties, blood samples were collected at 0, 10, 20, 30, and 45 minutes, and 1, 1.5, 3, 5, 8, 11, 18, 36, and 48 hour(s). The PK parameters, including C(max), T(max), t((1/2)), AUC(0-48), and AUC(0-infinity), were determined from the plasma concentrations of the 2 formulations by noncompartmental analysis. Tolerability was assessed at baseline (be- fore administration) and at 30 minutes and 1, 5, 18, and 48 hours after administration by monitoring vital signs. Laboratory tests (hematology, blood biochemistry, hepatic function, and urinalysis) were performed for the identification of adverse events (AEs) (eg, leukopenia, thrombocytopenia, anemia). Patient interviews were conducted to assess the occurrence of AEs such as diarrhea, abdominal pain, nausea, vomiting, and secondary infections. The formulations were considered to meet the regulatory requirements of bioequivalence if the log-transformed ratios of C(max) and AUC were within the predetermined equivalence range (80%-125%) as established by the US Food and Drug Administration (FDA).

RESULTS

Eighteen healthy Chinese male volunteers (mean [range] age, 23.5 [22-30] years; weight, 63.3 [56-68] kg; height, 171 [165-184] cm) were enrolled and completed the study. The main PK parameters of the MMF test and reference formulations were as follows: mean (SD) T(max), 0.68 (0.21) and 0.81 (0.18) hour, respectively; C(max), 25.58 (4.79) and 26.47 (3.67) mg/L; AUC(0-48), 59.19 (9.23) and 58.32 (9.28) mg/L/h; t((1/2)), 15.12 (3.17) and 16.04 (4.22) hours; AUC(0-infinity)), 63.28 (10.23) and 62.41 (10.28) mg/L/h. The mean (SD) relative bioavailability was 101.5% (10.3%). No statistically significant differences were found based on ANOVA. The ratios of C(max) (0.97) and AUC (1.01) for the test and reference formulations were within the FDA bioequivalence definition intervals of 80% to 125%. No AEs were reported by subjects or found on analysis of vital signs or laboratory tests.

CONCLUSIONS

In this study in healthy Chinese male volunteers, results from the PK analysis suggested that a single dose of the test and reference formulations of MMF 1.0 g met the regulatory requirements of bioequivalence, based on the FDA regulatory definition (rate and extent of absorption). Both formulations were well tolerated.

Limited sampling strategies for mycophenolic acid in solid organ transplantation: a systematic review

BACKGROUND

Mycophenolic acid (MPA) is the active metabolite of mycophenolate mofetil, a widely used immunosuppressant. Numerous studies have developed limited sampling strategies (LSSs) to predict MPA AUC in solid organ transplant recipients.

OBJECTIVES

To systematically review and assess quality of literature pertaining to MPA LSSs, evaluate clinical implications and provide suggestions for future research.

METHODS

Literature searches of MEDLINE (1966 - May 2009) and EMBASE (1980 - May 2009) for English articles in solid organ transplantation, along with manual review of article references were conducted. Included articles were categorized according to criteria adapted from levels of evidence of the US Preventative Services Task Force.

RESULTS

Of a total of 29 studies identified, 20 were in kidney, 4 in heart, 4 in liver and 1 in lung transplantation and 7 were in pediatrics. A total of 14 studies were deemed to be Level I evidence studies, 3 were Level II-1, 1 was Level II-2 and 11 were Level III.

CONCLUSIONS

Although various LSSs that are well correlated to MPA AUC while being relatively unbiased and precise to predict MPA AUC have been developed, further research is needed to determine validity of these LSSs in a variety of patient populations and to determine if these LSSs improve patient outcomes.

Limited sampling strategies for predicting area under the concentration-time curve of mycophenolic acid in islet transplant recipients

BACKGROUND

Mycophenolate mofetil is widely used in islet transplant recipients and its active metabolite, mycophenolic acid (MPA), exhibits wide pharmacokinetic variability. However, to our knowledge, no limited sampling strategy (LSS) exists for monitoring MPA in this subpopulation.

OBJECTIVE

To define optimal LSSs for MPA monitoring and to test their predictive performance in islet transplant recipients.

METHODS

After written informed consent was obtained and upon administration of a steady-state morning mycophenolate mofetil dose, blood samples were collected at 0, 0.3, 0.6, 1, 1.5, 2, 3, 4, 6, 8, 10, and 12 hours from 16 stable islet transplant recipients. MPA concentrations were measured by a validated high-performance liquid chromatography method with ultraviolet detection and pharmacokinetic parameters analyzed by noncompartmental modeling. All 16 patients' profiles were used to develop the LSSs via multiple regression analysis. Potential LSSs were restricted to ones having R(2) 0.90 or greater and 3 or fewer time points within the first 4 hours postdose. Resulting equations were validated for their predictive performance using the jackknife method, with acceptable criteria for bias and precision preset to within +/-15%. In addition, 14 published LSSs (in the renal transplant population) were tested in our islet transplant patients.

RESULTS

Five LSSs met preset criteria and had conventional sampling times: AUC = 1.783 + 1.248C1 + 0.888C2 + 8.027C4 (R2 = 0.98, bias = -3.09%, precision = 9.53%) AUC = 2.778 + 1.413C1 + 0.963C3 + 7.511C4 (R2 = 0.97, bias = -3.22%, precision = 11.02%) AUC = 1.448 + 1.239C1 + 0.271C1.5 + 9.108 C4 (R2 = 0.96, bias = -1.90%, precision = 11.46) AUC = 1.410 - 0.259C0 + 1.443C1 + 9.622C4 (R2 = 0.96, bias = -2.68%, precision = 11.53%) AUC = 1.547 + 1.417C1 + 9.448C4 (R2 = 0.96, bias = -2.46%, precision = 11.14%) where AUC = area under the concentration-time curve. None of the other published LSSs in the renal transplant population met the preset criteria for bias and precision.

CONCLUSIONS

To our knowledge, these are the first precise and accurate LSSs for predicting MPA AUC developed specifically for islet transplant recipients. The LSS that we recommend is the one utilizing 2 concentrations: AUC = 1.547 + 1.417C1 + 9.448C4. This equation is convenient and clinically feasible. Other islet transplant centers may wish to validate our equation in their population or use our template as a guide to develop accurate and precise LSSs specific to their patient population.

Pharmacokinetic role of protein binding of mycophenolic acid and its glucuronide metabolite in renal transplant recipients

Mycophenolic acid (MPA), the active compound of mycophenolate mofetil (MMF), is used to prevent graft rejection in renal transplant recipients. MPA is glucuronidated to the metabolite MPAG, which exhibits enterohepatic recirculation (EHC). MPA binds for 97% and MPAG binds for 82% to plasma proteins. Low plasma albumin concentrations, impaired renal function and coadministration of cyclosporine have been reported to be associated with increased clearance of MPA. The aim of the study was to develop a population pharmacokinetic model describing the relationship between MMF dose and total MPA (tMPA), unbound MPA (fMPA), total MPAG (tMPAG) and unbound MPAG (fMPAG). In this model the correlation between pharmacokinetic parameters and renal function, plasma albumin concentrations and cotreatment with cyclosporine was quantified. tMPA, fMPA, tMPAG and fMPAG concentration-time profiles of renal transplant recipients cotreated with cyclosporine (n = 48) and tacrolimus (n = 45) were analyzed using NONMEM. A 2- and 1-compartment model were used to describe the pharmacokinetics of fMPA and fMPAG. The central compartments of fMPA and fMPAG were connected with an albumin compartment allowing competitive binding (bMPA and bMPAG). tMPA and tMPAG were modeled as the sum of the bound and unbound concentrations. EHC was modeled by transport of fMPAG to a separate gallbladder compartment. This transport was decreased in case of cyclosporine cotreatment (P < 0.001). In the model, clearance of fMPAG decreased when creatinine clearance (CrCL) was reduced (P < 0.001), and albumin concentration was correlated with the maximum number of binding sites available for MPA and MPAG (P < 0.001). In patients with impaired renal function cotreated with cyclosporine the model adequately described that increasing fMPAG concentrations decreased tMPA AUC due to displacement of MPA from its binding sites. The accumulated MPAG could also be reconverted to MPA by the EHC, which caused increased tMPA AUC in patients cotreated with tacrolimus. Changes in CrCL had hardly any effect on fMPA exposure. A decrease in plasma albumin concentration from 0.6 to 0.4 mmol/l resulted in ca. 38% reduction of tMPA AUC, whereas no reduction in fMPA AUC was seen. In conclusion, a pharmacokinetic model has been developed which describes the relationship between dose and both total and free MPA exposure. The model adequately describes the influence of renal function, plasma albumin and cyclosporine co-medication on MPA exposure. Changes in protein binding due to altered renal function or plasma albumin concentrations influence tMPA exposure, whereas fMPA exposure is hardly affected.

Limited sampling strategies for therapeutic drug monitoring of mycophenolate mofetil therapy in patients with autoimmune disease

Mycophenolate mofetil (MMF) is increasingly used for the treatment of autoimmune diseases (AID). In renal transplant recipients, it has been demonstrated that adjustment of the MMF dose according to the area under the plasma concentration versus time curve (AUC) of mycophenolic acid (MPA), the active moiety of MMF, improves clinical outcome. The aim of this study was to develop a maximum a posteriori Bayesian estimator (MAP-BE) to estimate MPA AUC(0-12) in patients with AID using a limited number of samples. The predictive performance of the MAP-BE was compared with a multiple linear regression method. Full MPA concentration versus time curves were available from 38 patients with AID treated with MMF. Nonlinear mixed-effect modeling was used to develop a population pharmacokinetic model. Patients were divided in an index and a validation data set. The pharmacokinetic model derived from the index data set was used to develop several MAP-BEs. The Bayesian estimators were used to predict AUC(0-12) in the validation data set on the basis of a limited number of blood samples. The bias and precision of these predictions were compared with those of limited sampling strategies developed with multiple linear regression. The absorption of MPA was described with 2 first-order processes with a short and a long lag time and a subsequent first-order elimination. The 2-compartment model accounted for the enterohepatic recirculation of MPA as well. Using 1-4 samples, MPA AUC(0-12) was adequately estimated by the MAP-BE. Bias (-5.5%) was not significantly different from zero, and precision was below 27%. The predictive performance of the multiple linear regression method was comparable. In conclusion, MAP-BEs were developed for the estimation of MPA AUC(0-12) in patients with AID. The predictive performance was good and comparable to those of the multiple linear regression method. Due to its flexibility with respect to sample times, the MAP-BE may be preferred over the multiple linear regression method.

Determination of total, free and saliva mycophenolic acid with a LC-MS/MS method: application to pharmacokinetic study in healthy volunteers and renal transplant patients

Mycophenolic acid (MPA) is the active moiety of mycophenoate mofetil (MMF), an ester prodrug widely used as an immunosuppressant. Therapeutic drug monitoring (TDM) of MPA is becoming mandatory for transplant patients received MMF therapy in the routine clinical practice because of large individual variability, dose-related toxicity and the risk of acute rejection. In this study, a rapid, sensitive and selective LC-MS/MS method was developed and validated for the quantitative analysis of total and free MPA in plasma and in saliva that uses one identical liquid chromatographic and mass spectrometric condition. Following protein precipitation for total and saliva MPA, and ultrafiltration for free MPA, chromatographic separation was performed on an Allure PFP Propyl analytical column (100 x 2.1 mm, 5 microm, RESTEK Co., Bellefonte, PA, USA) with 0.1% formic acid in acetonitrile and 0.1% formic acid in water (45:55, v/v) as the mobile phases. The compounds were quantified by positive electrospray ionization tandem mass spectrometry. Selectivity, linearity, accuracy, precision, recovery, matrix effect, and saliva stability were evaluated during method validation. The validated method was applied to a pharmacokinetic study of MPA after an oral administration of a single 1000 mg of MMF to eight healthy male volunteers and 750 mg bid of MMF to nine renal transplant patients.

Population pharmacokinetic modelling for enterohepatic circulation of mycophenolic acid in healthy Chinese and the influence of polymorphisms in UGT1A9

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

Mycophenolic acid (MPA) undergoes enterohepatic circulation (EHC) in the body and several population models have been proposed to describe this process using sparse data. Recent studies in Whites have found that polymorphism in UGT1A9 could partly explain the large interindividual variability associated with the pharmacokinetics of MPA.

WHAT THIS STUDY ADDS

A new population pharmacokinetic model for EHC combining MPA and its main glucuronide metabolite (MPAG) simultaneously was established based on physiological aspects of biliary excretion using intensive sampling data. Pharmacokinetic profiles of MPA and MPAG with the UGT1A9 polymorphism in healthy Chinese were characterized. AIMS To establish a population pharmacokinetic model that describes enterohepatic circulation (EHC) of mycophenolic acid (MPA) based on physiological considerations and to investigate the influence of polymorphisms of UGT1A9 on the pharmacokinetics of MPA.

METHODS

Pharmacokinetic data were obtained from two comparative bioavailability studies of oral mycophenolic mofetil formulations. Nonlinear mixed effects modelling was employed to develop an EHC model including both MPA and its main glucuronide metabolite (MPAG) simultaneously. Demographic characteristics and UGT1A9 polymorphisms were screened as covariates.

RESULTS

In total, 590 MPA and 589 MPAG concentration-time points from 42 healthy male volunteers were employed in this study. The chain compartment model included an intestinal compartment, a gallbladder compartment, a central and a peripheral compartment for MPA and a central compartment for MPAG. The typical population clearance (CL/F) estimates with its relative standard error for MPA and MPAG were 10.2 l h(-1) (5.7%) and 1.38 l h(-1) (6.9%), respectively. The amount of MPA recycled in the body was estimated to be 29.1% of the total amount absorbed. Covariate analysis showed that body weight was positively correlated with CL/F of MPA, intercompartment CL/F of MPA and distribution volume of MPA peripheral compartment. Polymorphisms of UGT1A9 did not show any effect on the pharmacokinetics of MPA and MPAG. The model evaluation tests indicated that the proposed model can describe the pharmacokinetic profiles of MPA and MPAG in healthy Chinese subjects.

CONCLUSIONS

The proposed model may provide a valuable approach for planning future pharmacokinetic-pharmacodynamic studies and for designing proper dosage regimens of MPA.