Enteric-Coated Mycophenolate Sodium Provides Higher Mycophenolic Acid Predose Levels Compared With Mycophenolate Mofetil: Implications for Therapeutic Drug Monitoring

Model-informed precision dosing: State of the art and future perspectives

Model-informed precision dosing (MIPD) stands as a significant development in personalized medicine to tailor drug dosing to individual patient characteristics. MIPD moves beyond traditional therapeutic drug monitoring (TDM) by integrating mathematical predictions of dosing, and considering patient-specific factors (patient characteristics, drug measurements) as well as different sources of variability. For this purpose, rigorous model qualification is required for the application of MIPD in patients. This review delves into new methods in model selection and validation, also highlighting the role of machine learning in improving MIPD, the utilization of biosensors for real-time monitoring, as well as the potential of models integrating biomarkers for efficacy or toxicity for precision dosing. The clinical evidence of TDM and MIPD is discussed for various medical fields including infection medicine, oncology, transplant medicine, and inflammatory bowel diseases, thereby underscoring the role of pharmacokinetics/pharmacodynamics and specific biomarkers. Further research, particularly randomized clinical trials, is warranted to corroborate the value of MIPD in enhancing patient outcomes and advancing personalized medicine.

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.

Therapeutic drug monitoring of immunosuppressive drugs in hepatology and gastroenterology

Immunosuppressive drugs have been key to the success of liver transplantation and are essential components of the treatment of inflammatory bowel disease (IBD) and autoimmune hepatitis (AIH). For many but not all immunosuppressants, therapeutic drug monitoring (TDM) is recommended to guide therapy. In this article, the rationale and evidence for TDM of tacrolimus, mycophenolic acid, the mammalian target of rapamycin inhibitors, and azathioprine in liver transplantation, IBD, and AIH is reviewed. New developments, including algorithm-based/computer-assisted immunosuppressant dosing, measurement of immunosuppressants in alternative matrices for whole blood, and pharmacodynamic monitoring of these agents is discussed. It is expected that these novel techniques will be incorporate into the standard TDM in the next few years.

Model-informed precision dosing to optimise immunosuppressive therapy in renal transplantation

Immunosuppressive therapy is pivotal for sustained allograft and patient survival after renal transplantation. However, optimally balanced immunosuppressive therapy is challenged by between-patient and within-patient pharmacokinetic (PK) variability. This could warrant the application of personalised dosing strategies to optimise individual patient outcomes. Pharmacometrics, the science that investigates the xenobiotic-biotic interplay using computer-aided mathematical modelling, provides options to describe and quantify this PK variability and enables identification of patient characteristics affecting immunosuppressant PK and treatment outcomes. Here, we review and critically appraise the available pharmacometric model-informed dosing solutions for the typical immunosuppressants in modern renal transplantation, to guide their initial and subsequent dosing.

Personalized Therapy for Mycophenolate: Consensus Report by the International Association of Therapeutic Drug Monitoring and Clinical Toxicology

ABSTRACT

When mycophenolic acid (MPA) was originally marketed for immunosuppressive therapy, fixed doses were recommended by the manufacturer. Awareness of the potential for a more personalized dosing has led to development of methods to estimate MPA area under the curve based on the measurement of drug concentrations in only a few samples. This approach is feasible in the clinical routine and has proven successful in terms of correlation with outcome. However, the search for superior correlates has continued, and numerous studies in search of biomarkers that could better predict the perfect dosage for the individual patient have been published. As it was considered timely for an updated and comprehensive presentation of consensus on the status for personalized treatment with MPA, this report was prepared following an initiative from members of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology (IATDMCT). Topics included are the criteria for analytics, methods to estimate exposure including pharmacometrics, the potential influence of pharmacogenetics, development of biomarkers, and the practical aspects of implementation of target concentration intervention. For selected topics with sufficient evidence, such as the application of limited sampling strategies for MPA area under the curve, graded recommendations on target ranges are presented. To provide a comprehensive review, this report also includes updates on the status of potential biomarkers including those which may be promising but with a low level of evidence. In view of the fact that there are very few new immunosuppressive drugs under development for the transplant field, it is likely that MPA will continue to be prescribed on a large scale in the upcoming years. Discontinuation of therapy due to adverse effects is relatively common, increasing the risk for late rejections, which may contribute to graft loss. Therefore, the continued search for innovative methods to better personalize MPA dosage is warranted.

Pharmacokinetics of mycophenolate sodium co-administered with tacrolimus in the first year after renal transplantation

We assessed the relations between MPA, free MPA (fMPA) and MPA glucuronide (MPAG) pharmacokinetics and the clinical condition of renal transplant recipients treated with EC-MPS and tacrolimus (Tac) in the first post-transplant year. In 18 adult patients blood samples were collected up to 12 h after EC-MPS oral administration. EC-MPS metabolites' plasma concentrations were determined using validated HPLC methods. All patients reached MPA area under the time-concentration curve (AUC0-12) above 30 µg h/mL. Most of the MPA, fMPA and all MPAG concentrations correlated significantly with respective AUC0-12 values. Some fMPA and all MPAG pharmacokinetic parameters correlated negatively with creatinine clearance and positively with creatinine concentration, whereas no such correlation was observed for MPA. Lower hemoglobin concentrations were observed in patients with higher MPA or fMPA C 0. The significant correlations between MPA C 3 as well as MPA C 4 and MPA AUC0-4 and MPA AUC0-12 may be of importance in further studies including larger number of patients in regard to establishing LSS. In patients treated with EC-MPS and Tac, monitoring MPA C 0 may be important, as too high MPA C 0 may contribute to anemia onset. In EC-MPS treated patients, MPAG concentration is related to renal function as MPAG pharmacokinetics were higher in patients with renal impairment.

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.

Development and validation of limited sampling strategies for the estimation of mycophenolic acid area under the curve in adult kidney and liver transplant recipients receiving concomitant enteric-coated mycophenolate sodium and tacrolimus

BACKGROUND

Mycophenolic acid (MPA) is widely used in solid organ transplantation. MPA absorption from enteric-coated mycophenolate sodium (EC-MPS) is delayed, which results in a delayed enterohepatic recirculation and subsequently higher and more variable MPA 12-hour trough concentration and tmax values. Therefore, MPA trough level monitoring cannot be used to monitor MPA exposure in patients who are given EC-MPS. The aim of the study was to develop and validate a limited sampling strategy (LSS) for accurate prediction of the 12-hour area under the concentration-time curve (AUC0-12h) for MPA in patients who receive concomitant EC-MPS and Tacrolimus (Prograf or Advagraf) within 196 months posttransplantation. According to our knowledge, the LSS for MPA AUC estimation using high-performance liquid chromatography to determine MPA concentrations in plasma samples of kidney and liver transplant patients receiving EC-MPS and Tacrolimus (Advagraf) has not been previously evaluated.

METHODS

Seventy-four renal and liver transplant patients receiving EC-MPS and concomitant tacrolimus (either Prograf or Advagraf) provided a total of 74 pharmacokinetic profiles. MPA concentrations were measured using a validated high-performance liquid chromatography method for 9 plasma samples collected at predose and at 0.5, 1, 2, 3, 4, 6, 9, and 12 hours after the morning dose of EC-MPS after an overnight fast. LSS were developed and validated by stepwise multiple regression analysis with the use of a 2-group method (test, n = 37; and validation, n = 37).

RESULTS

The 3 and 4 time point equations using C1h, C3h, C9h and C1h, C2h, C3h, C6h, respectively, were found to be superior to all other models tested. When these LSS models were tested in the validation group, the results were acceptable [for 3 time points equation: r = 0.824, percentage of prediction error: 6.32 ± 25.75, 95% confidence interval (CI): -40.71 to 79.76; percentage of absolute prediction error: 27.45 ± 29.89, 95% CI: 0.04-199.92, predictive performance, 71% of estimated AUCs comprised within 85%-115% of the measured full MPA AUC, natural logarithmic residuals (ln) mean ± SD: -0.03 ± 0.24; for 4 time points equation: r = 0.898, percentage of prediction error: 3.32 ± 18.26, 95% CI: -49.35 to 51.06; percentage of absolute prediction error: 14.05 ± 11.89, 95% CI 0.13-49.86, percentage of predictive performance, 83% of estimated AUCs comprised within 85%-115% of the measured full MPA AUC, natural logarithmic residuals (ln) mean ± SD: -0.01 ± 0.19].

CONCLUSIONS

LSS equations using concentrations at 1, 3, and 9 hours or 1, 2, 3, and 6 hours time points provided the most reliable and accurate estimations of the MPA AUC in stable renal and liver transplant recipients treated with EC-MPS and tacrolimus. Further studies on independent groups of patients are required to confirm clinical utility of the presented LSS models.

Pharmacology and toxicology of mycophenolate in organ transplant recipients: an update

This review aims to provide an update of the literature on the pharmacology and toxicology of mycophenolate in solid organ transplant recipients. Mycophenolate is now the antimetabolite of choice in immunosuppressant regimens in transplant recipients. The active drug moiety mycophenolic acid (MPA) is available as an ester pro-drug and an enteric-coated sodium salt. MPA is a competitive, selective and reversible inhibitor of inosine-5'-monophosphate dehydrogenase (IMPDH), an important rate-limiting enzyme in purine synthesis. MPA suppresses T and B lymphocyte proliferation; it also decreases expression of glycoproteins and adhesion molecules responsible for recruiting monocytes and lymphocytes to sites of inflammation and graft rejection; and may destroy activated lymphocytes by induction of a necrotic signal. Improved long-term allograft survival has been demonstrated for MPA and may be due to inhibition of monocyte chemoattractant protein 1 or fibroblast proliferation. Recent research also suggested a differential effect of mycophenolate on the regulatory T cell/helper T cell balance which could potentially encourage immune tolerance. Lower exposure to calcineurin inhibitors (renal sparing) appears to be possible with concomitant use of MPA in renal transplant recipients without undue risk of rejection. MPA displays large between- and within-subject pharmacokinetic variability. At least three studies have now reported that MPA exhibits nonlinear pharmacokinetics, with bioavailability decreasing significantly with increasing doses, perhaps due to saturable absorption processes or saturable enterohepatic recirculation. The role of therapeutic drug monitoring (TDM) is still controversial and the ability of routine MPA TDM to improve long-term graft survival and patient outcomes is largely unknown. MPA monitoring may be more important in high-immunological recipients, those on calcineurin-inhibitor-sparing regimens and in whom unexpected rejection or infections have occurred. The majority of pharmacodynamic data on MPA has been obtained in patients receiving MMF therapy in the first year after kidney transplantation. Low MPA area under the concentration time from 0 to 12 h post-dose (AUC0-12) is associated with increased incidence of biopsy-proven acute rejection although AUC0-12 optimal cut-off values vary across study populations. IMPDH monitoring to identify individuals at increased risk of rejection shows some promise but is still in the experimental stage. A relationship between MPA exposure and adverse events was identified in some but not all studies. Genetic variants within genes involved in MPA metabolism (UGT1A9, UGT1A8, UGT2B7), cellular transportation (SLCOB1, SLCO1B3, ABCC2) and targets (IMPDH) have been reported to effect MPA pharmacokinetics and/or response in some studies; however, larger studies across different ethnic groups that take into account genetic linkage and drug interactions that can alter a patient's phenotype are needed before any clinical recommendations based on patient genotype can be formulated. There is little data on the pharmacology and toxicology of MPA in older and paediatric transplant recipients.

Pharmacokinetics and pharmacodynamics of mycophenolate sodium (EC-MPS) co-administered with cyclosporine in the early-phase post-kidney transplantation

Mycophenolate drug levels are decreased by co-administration of cyclosporine. However, mycophenolate levels may be associated with insufficient immunosuppression. We investigated the pharmacokinetics of 720 mg mycophenolate sodium (EC-MPS) and inosine monophosphate dehydrogenase (IMPDH) activity under co-medication with cyclosporine and steroids within the first 30 d after kidney transplantation (n = 24). Blood samples were drawn at 0, 0.5, 1, 1.5, 2, 3, 4, 6, 8, and 12 h after the morning dose. Plasma concentrations of mycophenolic acid, its glucuronide metabolites (MPAG; AcMPAG), and free MPA were determined using validated HPLC-DAD. IMPDH activity in leukocytes was analyzed chromatographically. Only six of 24 patients had an MPA-AUC(12h) within the putative therapeutic range of 40-60 mg/L·h. MPA clearance was high with 29 L/h. fMPA-AUC(12h) (r = -0.429, p = 0.04) and MPAG-AUC(12h) correlated significantly with the glomerular filtration rate, while total MPA did not. The MPAG-AUC(12h) was about 52-fold higher than the corresponding values for MPA, whereas the AcMPAG-AUC(12h) reached about 20.4% of the respective MPA-AUC(12h.) We found significant correlations between IMPDH inhibition and MPA concentration (r = -0.665; p < 0.0001), fMPA (r = -0.446; p = 0.003), and AcMPAG (r = -0.459; p = 0.002) but not with MPAG. Only 25% of the patients attained the therapeutic range for MPA-AUC under standard EC-MPS dose during the early-phase post-transplantation. We recommend that EC-MPS should be given in higher doses (3 × 720 mg) in the early post-transplant period when co-administered with cyclosporine.

Efficacy and safety of conversion of mycophenolate mofetil to enteric-coated mycophenolate sodium in Mexican renal transplant children

The aim of the study was to evaluate the efficacy and safety of the conversion of MMF to EC-MPS in pediatric renal transplant recipients. We included 12 patients with stable graft function who were receiving MMF treatment. In the first visit, a complete medical examination was performed, which included a GSRS, a nine-point pharmacokinetic profile, samples for renal, liver and hematological tests and evaluation of IMPDH2 gene expression. The patients were transferred to an equimolar dose of EC-MPS. Two wk later, a clinical evaluation and blood collection, as in the first visit were performed. There was no change in serum creatinine, leukocyte count, serum albumin, or transaminase levels, but we found a statistically significant reduction of hemoglobin after conversion (13.2 +/- 1.6 g/dL with MMF vs. 12.5 +/- 1.3 g/dL when receiving EC-MPS). The GSRS total mean score was 16 +/- 12 with MMF vs. 8 +/- 5 with EC-MPA (p < 0.05). There was no statistically significant difference between formulations in the gene expression of IMPDH 2, in the AUC(0-12h) or in C(max). However, peak concentration occurred later with EC-MPS.

Limited sampling strategies drawn within 3 hours postdose poorly predict mycophenolic acid area-under-the-curve after enteric-coated mycophenolate sodium

Previous studies predicted that limited sampling strategies (LSS) for estimation of mycophenolic acid (MPA) area-under-the-curve (AUC(0-12)) after ingestion of enteric-coated mycophenolate sodium (EC-MPS) using a clinically feasible sampling scheme may have poor predictive performance. Failure of LSS was thought to be due to the slow absorption of MPA causing late and variable times of maximum MPA concentration and variable predose concentrations. The aim of this study was to formally test the performance of LSS by developing and validating LSS for estimation of MPA AUC(0-12) after EC-MPS administration. Pharmacokinetic data from 109 renal transplant recipients collected during the maintenance period after transplantation were analysed retrospectively. LSS were developed separately for renal transplant patients who concurrently used cyclosporine (n = 79) and for patients not concurrently treated with cyclosporine (n = 30). Data were split into an index and a validation data set. For clinical feasibility reasons, a LSS could consist of a maximum of 3 sampling time points with the latest sample drawn 2 hours after drug administration. LSS with the latest sample drawn 3 hours after drug administration or even later were also tested. The validation of the developed LSS showed that MPA AUC(0-12) for patients concurrently treated with cyclosporine was best estimated by AUC(0-12) (mg x h x L(-1)) = 36.536 + 1.642 x C0.5 + 0.569 x C1.5 + 0.905 x C2 (r2 = 0.33, bias = -1.0 mg x h x L(-1), precision = 24 mg x h x L(-1)), whereas AUC(0-12) [mg x h x L(-1)] = 19.801 + 1.827 x C0.5 + 1.111 x C1 + 1.429 x C2 was the best AUC(0-12) estimator for patients not cotreated with cyclosporine (r2 = 0.31, bias = 0.4 mg x h x L(-1), precision = 14.5 mg x h x L(-1)). Both LSS showed poor precision and overestimation of AUC(0-12) values below the therapeutic window and underestimation of AUC(0-12) values above the therapeutic window of MPA. Using C3 as latest sampling time point improved the fit slightly, but not satisfactory, with r2 still <0.40 and precision still >14.0 mg x h x L(-1). Estimation of MPA AUC(0-12) with LSS for EC-MPS drawn within 2 or 3 hours postdose in renal transplant recipients in the maintenance period is likely to result in biased and imprecise results.

Adverse drug reaction driven immunosuppressive drug manipulations: a single-center comparison of enteric-coated mycophenolate sodium vs. mycophenolate mofetil

Enteric-coated mycophenolate sodium (MPS) has been developed to help circumvent the upper gastrointestinal side-effects of mycophenolic acid by facilitating drug release in the small intestine. Many questions regarding the side-effect profile of MPS remain. Therefore, the purpose of this study is to review a single-center's experience with mycophenolate mofetil (MMF) and MPS.

METHODS

This retrospective, sequential cohort analysis of de novo renal and pancreas transplants (n = 198) compared MMF 500 mg b.i.d. to MPS 360 mg b.i.d. in conjunction with antibody induction, tacrolimus, and steroids.

RESULTS

There were fewer adverse event driven drug manipulations in the MPS group at 90 d (4% MPS vs. 17% MMF) and 180 d (10% MPS vs. 24% MMF, p = 0.006, log-rank) after transplantation. There was a trend toward fewer GI-related hospital admissions in the MPS arm (7% MPS vs. 13% MMF, p = 0.18). Allograft outcomes including patient survival, graft survival, acute rejection, serum creatinine, and infection were similar.

CONCLUSION

This single-center, sequential cohort study demonstrates that MPS is associated with fewer adverse event driven drug manipulations while maintaining similar safety and allograft outcomes.