Population pharmacokinetics of mycophenolic acid in pediatric patients with juvenile dermatomyositis and optimization of limited sampling strategy

Bioequivalue of two mycophenolate sodium enteric-coated tablets and the drug monitoring based on limited sampling strategy: A single-center, randomized, open-label, three-period, reference-replicated, crossover study

OBJECTIVE

A mycophenolate sodium enteric-coated tablet has shown a satisfying anti-rejection effect in patients receiving solid organ transplantation. The current study evaluated the bioequivalence between the test (Ruiyirong®) vs. reference (Myfortic®) formulations by exploring equations for predicting their area under the concentration-time curve (AUC) using a limited sampling strategy in healthy subjects.

METHODS

Forty-eight healthy Chinese subjects were randomized into three administration sequences (test-reference-reference, reference-reference-test, and reference-test-reference) to receive the Ruiyirong or Myfortic treatment on days 1, 8, and 15.

RESULTS

The 90% confidential interval (CI) of the geometric mean ratios (test/reference) of maximum plasma concentration (Cmax), the AUC from time 0 to the last timepoint (AUC0-t), and the AUC from 0 to infinity (AUC0-∞) was 92.90%-110.57%, 96.91%- 101.80%, and 96.71%-101.84%, respectively. All these values fell into the bioequivalence criteria of 80.00%-125.00% (based on the criteria of the Food and Drug Administration). The adverse events were 10.4% in Ruiyirong test group and 14.6% in Myfortic reference group. Eight equations for estimating the AUC of the Ruiyirong test and Myfortic reference formulations were evaluated; most of them worked well with the R-value >0.8. Among the four chosen equations, the intragroup verification exhibited a high agreement with the R-value ranging from 0.857 to 0.971 and with the low predictive error (PE > 5% with absolute PE > 15%). Meanwhile, the intergroup verification indicated a high inter-agreement with the R-value ranging from 0.896 to 0.974 (all P < 0.001).

CONCLUSION

The Ruiyirong test vs. Myfortic reference formulations meet the bioequivalent criteria and are well tolerated. The further linear regression analysis explores eight equations predicting the AUC value and the chosen four equations for the Ruiyirong test and Mayfortic reference formulations are interchangeable.

Significant Effects of Renal Function on Mycophenolic Acid Total Clearance in Pediatric Kidney Transplant Recipients with Population Pharmacokinetic Modeling

BACKGROUND AND OBJECTIVES

Mycophenolic acid (MPA) is an immunosuppressant commonly prescribed in pediatric kidney transplantation to prevent graft rejection. Large variabilities in MPA plasma exposures have been observed in this population, which could result in severe adverse effects. The majority of the MPA pharmacokinetic data have been reported in adult populations, whereas information in pediatric patients is still very limited. The objective of this study was to establish a novel, nonlinear mixed-effects model for MPA and investigate the clinical variables affecting MPA population pharmacokinetics in pediatric kidney transplant recipients.

METHODS

Data were collected retrospectively from pediatric kidney transplant patients (≤ 18 years when MPA concentrations were initially collected; on oral administration of mycophenolate mofetil) in Calgary, Alberta, Canada. Nonlinear mixed-effect modeling was conducted using stochastic approximation expectation-maximization in Monolix 2021R2 (Lixoft SAS, France) to determine population pharmacokinetic estimates, interindividual variabilities, and interoccasional variabilities. Covariate models were constructed using the Model Proposal function in Monolix in conjunction with a systematic stepwise inclusion/elimination protocol. The best model was selected based on objective function values, relative standard errors, goodness-of-fit plots, prediction-corrected visual predictive checks, and numerical predictive checks.

RESULTS

A total of 50 pediatric kidney transplant patients (25 female) with 219 MPA plasma concentration-time profiles were included. The average age (± standard deviation) and posttransplant time for the sample population were 12.8 ± 4.8 years and 762 ± 1160 days, respectively. The majority of study subjects (i.e., > 85% based on all occasions) were co-administered tacrolimus. A two-compartment, first-order absorption with lag time and linear elimination structural model with lognormal distributed proportional residual errors best described the MPA concentration-time data. The absorption rate constant (2.52 h-1 or 0.042 min-1), lag time (0.166 h or 9.96 min), volumes of distributions of the central (22.8 L) and peripheral (216 L) compartments, and intercompartment clearance (17.6 L h-1 or 0.293 L min-1) were consistent with literature values; whereas total MPA clearance (0.72 L h-1 or 0.012 L min-1) was relatively reduced, likely due to the general lack of cyclosporine interactions and the stabilized graft functions from significantly longer posttransplant time in our sample population. Of the clinical variables tested, only estimated glomerular filtration rate (eGFR) was identified a significant covariate affecting total MPA clearance with a positive, exponential relationship. The final population pharmacokinetic model was successfully evaluated/validated using a variety of complementary methods.

CONCLUSION

We have successfully constructed and validated a novel population pharmacokinetic model of MPA in pediatric kidney transplant patients. A positive, nonlinear relationship between eGFR and total MPA clearance identified in our model is likely attributed to multiple concurrent mechanisms, which warrant further systematic investigations.

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.

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.