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

The reduced function allele SLCO1B1 c.521T>C is of no practical relevance for the renal graft function over the first post-transplant year in patients treated with mycophenolic acid

OBJECTIVE

It is unclear whether renal transplant recipients treated with mycophenolic acid (MPA) who carry the reduced-function allele at polymorphism SLCO1B1 c.521T>C differ from their wild-type peers regarding renal outcomes and tolerability. We aimed to estimate the effect of this polymorphism on the graft function (estimated glomerular filtration rate, eGFR) over the first 12 post-transplant months in patients on MPA-based maintenance immunosuppression.

METHODS

In a 12-month observational cohort study, consecutive adult patients were repeatedly assessed for eGFR. The SLCO1B1 c.521C>T variant allele carriers (exposed) and wild-type subjects (controls) were balanced on a range of demographic, medical, and genetic variables at baseline, and eGFR trajectory was estimated with further adjustment for time-varying covariates. A subset of patients were assessed for exposure to MPA 5-7 days after the transplantation.

RESULTS

The adjusted eGFR slopes from day 1 to day 28 (daily), and from day 28 to day 365 (monthly) were practically identical in exposed (n = 86) and control (n = 168) patients [geometric means ratios (GMR) = 0.99, 95% confidence interval (CI) = 0.92-1.06 and GMR = 0.98, 0.94-1.01, respectively]. The rates of adverse renal outcomes and possible MPA-related adverse effects were low, and similar in exposed and controls [rate ratios (RR) = 0.94, 0.49-1.84 and RR = 1.08, 0.74-1.58, respectively]. The pharmacokinetic analysis did not signal meaningful differences regarding exposure to MPA, overall (exposed n = 23, control n = 45), if cotreated with cyclosporine (n = 17 vs. n = 26) or with tacrolimus (n = 8 vs. n = 17).

CONCLUSIONS

In patients treated with MPA, variant allele SLCO1B1 c.521T>C appears of no practical relevance regarding the 12-month renal graft function, MPA safety and exposure to MPA at early steady-state.

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

BACKGROUND

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.

METHODS

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.

RESULTS

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%).

CONCLUSIONS

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.

Inosine monophosphate dehydrogenase type 2 polymorphism IMPDH2 3757T>C (rs11706052) and 12-month evolution of the graft function in renal transplant recipients on mycophenolate-based immunosuppression

Variant allele at the inosine monophosphate dehydrogenase type 2 polymorphism IMPDH2 3757T>C has been associated with increased enzyme activity and reduced susceptibility to mycophenolic acid (MPA) in vitro. It has been suggested associated with an increased risk of acute rejection in renal transplant recipients on MPA-based immunosuppression, but not unambiguously. We assessed one-year evolution of the estimated glomerular filtration rate (eGFR) in transplanted variant allele carriers and wild-type subjects, while controlling for a number of demographic, pharmacogenetic, (co)morbidity, and treatment baseline and time-varying covariates. The eGFR slopes to day 28 (GMR = 1.01, 95% CI 0.93-1.09), and between days 28 and 365 (GMR = 1.01, 95% CI 0.99-1.02) were practically identical in 52 variant carriers and 202 wild-type controls. The estimates (95%CIs) remained within the limits of ±20% difference even after adjustment for a strong hypothetical effect of unmeasured confounders. Polymorphism IMPDH2 3757T>C does not affect the renal graft function over the 1st year after transplantation.

Mycophenolate mofetil increases the risk of diarrhea in allogeneic hematopoietic stem cell transplantation recipients

OBJECTIVES

Mycophenolate mofetil (MMF) was reported to be a main cause of diarrhea following organ transplantation. However, research on MMF-induced diarrhea following allogeneic hematopoietic stem cell transplantation (allo-HSCT) is currently insufficient. This retrospective study examined the incidence of MMF-induced diarrhea among allo-HSCT recipients.

METHODS

Recipients were divided according to the receipt of MMF and the appearance of diarrhea. The differences in clinical information, MMF usage and trough concentrations, and the occurrence of diarrhea from the first day of conditioning treatment to 100 days after transplantation were analyzed.

RESULTS

In total, 32.9% of the recipients reported diarrhea. The incidence rate of diarrhea was higher in the MMF group than in the non-MMF group (40.0% vs. 16.7%). MMF-induced diarrhea usually occurred within 9 days of MMF initiation and persisted for 7.27 ± 3.54 days. The average body weight, MMF daily dose, and MMF trough concentration were higher in patients with diarrhea.

CONCLUSION

MMF increased the risk of diarrhea in allo-HSCT recipients, and the risk was related to the MMF dose and trough concentration. The difference in onset time could be a basis for identifying the cause of diarrhea in allo-HSCT recipients.

Influence of Calcineurin Inhibitors and Genetic Polymorphism of Transporters on Enterohepatic Circulation and Exposure of Mycophenolic Acid in Chinese Adult Renal Allograft Recipients

There is significant enterohepatic circulation (EHC) during the disposition of mycophenolic acid (MPA). The aim of this study was to elucidate factors influencing the EHC of MPA in Chinese adult renal allograft recipients. After 2 weeks of therapy with mycophenolate mofetil or enteric-coated mycophenolate sodium, blood samples were collected from 125 patients at 0 to 12 hours post-administration and MPA concentrations were determined. The influence of calcineurin inhibitors (CNIs) and genetic polymorphisms on MPA exposure and EHC was studied. The Shapley additive explanations method was used to estimate the impact of various factors on the area under the plasma drug concentration-time curve (AUC_0-12h ) for MPA. An extreme gradient boosting (XGboost) machine learning-based model was established to predict AUC_0-12h . Results showed that the dose-normalized AUC_6-12h (dn-AUC_6-12h ) of MPA was significantly lower in patients co-administered with cyclosporine (CsA) than in patients co-administered with tacrolimus (TAC) (P < .05). For patients co-administered with TAC, patients with ABCC2 C-24T CC or SLCO1B1 T521C TT genotypes had significantly higher values of dn-AUC_6-12h (P < .05). Patients with SLCO1B3 334T/699G alleles had significantly lower dn-AUC_6-12h values than homozygotes (P < .05). By introducing body weight, age, and EHC-related factors, including co-administered CNIs and genetic polymorphism of drug transporters, as covariates in the XGboost machine learning model, the prediction performance of AUC_0-12h for MPA in Chinese adult renal allograft recipients can be improved.

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

BACKGROUND

For 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.

METHODS

The 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.

RESULTS

The 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.

CONCLUSIONS

The 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.

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.

Population pharmacokinetics and limited sampling strategy for therapeutic drug monitoring of mycophenolate mofetil in Japanese patients with lupus nephritis

BACKGROUND

Mycophenolate mofetil (MMF), a prodrug of the immunosuppressive agent mycophenolic acid (MPA), is difficult to administer because of the pharmacokinetic complexity of MPA. Although dosage adjustment according to the 12-h area under the concentration-time curve (AUC_0-12) is thought to be desirable, multiple blood samplings for AUC calculation may pose a clinical challenge. A limited sampling strategy (LSS) would provide a solution; however, little is known about MPA pharmacokinetics in lupus nephritis patients, especially in those with Asian backgrounds, or few, if any, LSSs are reported for them.

METHODS

Thirty-four adult Japanese patients receiving MMF for lupus nephritis were examined retrospectively. MPA pharmacokinetics were investigated, and a PPK model was developed using Phoenix® NLME™ software. Single and double blood sampling strategies from Bayesian estimation using the PPK model and from multiple linear regression were compared. Tolerability was also evaluated.

RESULTS

In the pharmacokinetic analysis, renal function and serum albumin had significant effects on dose-normalized AUC_0-12; and serum albumin, concomitant proton pump inhibitor (PPI) and iron/magnesium oxide did on dose-normalized maximum concentration. As a PPK model, a two-compartment model was developed with a transit absorption model and first-order elimination, in which creatinine clearance and serum albumin were covariates for MPA clearance. The double sampling strategy at 1 and 4 h by multiple linear regression showed the best agreement with the observed AUC_0-12 (r² = 0.885). Of the single sampling strategies, the one at 6 h by Bayesian estimation performed best (r² = 0.769). The tolerability evaluation showed that correlations were suggested for gastrointestinal involvement.

CONCLUSIONS

The present study developed the first PPK model of MPA for Japanese lupus nephritis patients. As for LSSs, a double sampling strategy at 1 and 4 h by multiple linear regression would work best; when only a single blood sampling is allowed, a strategy at 6 h by Bayesian estimation using the PPK model developed in this study would be best. The LSSs good enough for clinical use may facilitate safer, more effective, and individualized therapy.

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.

Population Pharmacokinetics of Enteric-Coated Mycophenolate Sodium in Children after Renal Transplantation and Initial Dosage Recommendation Based on Body Surface Area

Objective

Enteric-coated mycophenolate sodium (EC-MPS) is widely used in renal transplant recipients. There is a lack of study on the pharmacokinetics of this drug in children. This study is aimed at developing a population pharmacokinetic model of mycophenolic acid in children who were treated with EC-MPS after renal transplantation and to recommend initial dosage.

Methods

Pediatric patients who had undergone renal transplantation and received EC-MPS were included. Data on demographic characteristics, biochemical tests, blood routine examinations, mycophenolic acid plasma concentrations, dosing amount and frequency of EC-MPS, and coadministered medications were retrospective collected from June 2018 to August 2019. Nonlinear mixed effect modeling methods were adopted to develop a population pharmacokinetic model with the data above. Additional data from September 2019 to July 2020 were used to validate the model. Simulations under different dosage regimen were conducted to evaluate the percentage of target attainment (PTA, AUC_0-12h 30–60 mg·h/L).

Results

A total of 96 pediatric patients aged at 13.3 (range 4.3–18.0) years were included in the modeling group. Data from 32 patients aged at 13.0 (range 3.6–18.3) years were used to validate the model. A one-compartment model with a double extravascular absorption was developed. Body surface area (BSA) was added as a covariate. Simulations showed that for different dosing regimens, the highest percentage of target attainment is around 50%. The best dosing regimen is 180 mg every 48 hours for patients with BSA of 0.22–0.46 m², 180 mg every 24 hours with BSA of 0.47–0.67 m², 180 mg every 24 hours with BSA of 0.68–0.96 m², 360 mg every 24 hours with BSA of 0.97–1.18 m², 540 mg every 24 hours with BSA of 1.19–1.58 m², and 360 mg every 12 hours with BSA of 1.59–2.03 m².

Conclusion

BSA could affect the area under curve of mycophenolic acid with the administration of EC-MPS. Considering the inflexibility of the dosage form, future development of smaller amount per tablet suitable for younger children with BSA < 1.19 m² is warranted.

The Efficacy and Safety of Mizoribine versus Mycophenolate Mofetil for the Treatment of Renal Transplantation: A Systematic Review and Meta-Analysis

Background

Mizoribine (MZR) is widely used in Asia due to its high safety and low cost, and comparative studies of its safety and efficacy with the first-line drug mycophenolate mofetil (MMF) have been carried out. This paper aimed to compare the efficacy and safety of MZR and MMF in immunosuppressive therapy of renal transplantation by meta-analysis.

Methods

We searched randomized controlled trials (RCTs) comparing MZR versus MMF for renal transplantation in PubMed, Excerpta Medica Database (EMBASE), Cochrane Library, Web of Science, WanFang Database, China National Knowledge Infrastructure (CNKI), and Chinese Biomedical Database (CBM). Articles were assessed for their risk of bias using the Cochrane Collaboration. Forest plots and funnel plots were also performed on the included articles.

Results

A total of twelve studies with 1103 patients were selected in the analysis. No significant difference were observed between the MZR group and the MMF group for the rate of acute rejection (RR = 1.50, 95% CI 1.11 to 2.01, P = 0.008), patient survival (RR = 1.01, 95% CI 0.99 to 1.03, P = 0.56), graft survival (RR = 1.02, 95% CI 1.00 to 1.04, P = 0.12), leucopenia (RR = 0.69, 95% CI 0.44 to 1.10, P = 0.12), and liver damage (RR = 0.72, 95% CI 0.46 to 1.13, P = 0.15). The MZR group was associated with a lower risk of gastrointestinal disorder (RR = 0.28, 95% CI 0.13 to 0.62, P = 0.002) and cytomegalovirus infection (RR = 0.59, 95% CI 0.42 to 0.84, P = 0.003) but had a higher risk of hyperuricemia (RR 1.79, 95% CI 1.17 to 2.75, P = 0.007). No significant publication bias was observed among included studies. Discussion. MZR is similar to MMF in efficacy, and in terms of safety, MZR has a lower risk of gastrointestinal disorder and cytomegalovirus infection but a higher risk of hyperuricemia.

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.