Pharmacokinetics and target attainment of mycophenolate in pediatric renal transplant patients

Liquid chromatography-tandem mass spectrometry method for mycophenolic acid and its glucuronide determination in saliva samples from children with nephrotic syndrome

BACKGROUND

Saliva sampling is one of the methods of therapeutic drug monitoring for mycophenolic acid (MPA) and its metabolite, mycophenolic acid glucuronide (MPAG). The study describes the liquid chromatography tandem mass spectrometry (LC-MS/MS) method developed for saliva MPA and MPAG determination in children with nephrotic syndrome.

METHODS

The mobile phase consisted of methanol and water at gradient flow, both with 0.1% formic acid. Firstly, 100 µL of saliva was evaporated at 45 °C for 2 h to dryness, secondly, it was reconstituted in the mobile phase, and finally 10 µL was injected into the LC-MS/MS system. Saliva from ten children with nephrotic syndrome treated with mycophenolate mofetil was collected with Salivette®.

RESULTS

For MPA and MPAG, within the 2-500 ng/mL range, the method was selective, specific, accurate and precise within-run and between-run. No carry-over and matrix effects were observed. Stability tests showed that MPA and MPAG were stable in saliva samples if stored for 2 h at room temperature, 18 h at 4 °C, and at least 5 months at - 80 °C as well as after three freeze-thaw cycles, in a dry extract for 16 h at 4 °C, and for 8 h at 15 °C in the autosampler. The analytes were not adsorbed onto Salivette® cotton swabs. For concentrations above 500 ng/mL, the samples may be diluted twofold. In children, saliva MPA and MPAG were within the ranges of 4.6-531.8 ng/mL and 10.7-183.7 ng/mL, respectively.

CONCLUSIONS

The evaluated LC-MS/MS method has met the validation requirements for saliva MPA and MPAG determination in children with nephrotic syndrome. Further studies are needed to explore plasma-saliva correlations and assess their potential contribution to MPA monitoring.

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.

Noninvasive testing for mycophenolate exposure in children with renal transplant using urinary metabolomics

BACKGROUND

Despite the common use of mycophenolate in pediatric renal transplantation, lack of effective therapeuic drug monitoring increases uncertainty over optimal drug exposure and risk for adverse reactions. This study aims to develop a novel urine test to estimate MPA exposure based using metabolomics.

METHODS

Urine samples obtained on the same day of MPA pharmacokinetic testing from two prospective cohorts of pediatric kidney transplant recipients were assayed for 133 unique metabolites by mass spectrometry. Partial least squares (PLS) discriminate analysis was used to develop a top 10 urinary metabolite classifier that estimates MPA exposure. An independent cohort was used to test pharmacodynamic validity for allograft inflammation (urinary CXCL10 levels) and eGFR ratio (12mo/1mo eGFR) at 1 year.

RESULTS

Fifty-two urine samples from separate children (36.5% female, 12.0 ± 5.3 years at transplant) were evaluated at 1.6 ± 2.5 years post-transplant. Using all detected metabolites (n = 90), the classifier exhibited strong association with MPA AUC by principal component regression (r = 0.56, p < .001) and PLS (r = 0.75, p < .001). A practical classifier (top 10 metabolites; r = 0.64, p < .001) retained similar accuracy after cross-validation (LOOCV; r = 0.52, p < .001). When applied to an independent cohort (n = 97 patients, 1053 samples), estimated mean MPA exposure over Year 1 was inversely associated with mean urinary CXCL10:Cr (r = -0.28, 95% CI -0.45, -0.08) and exhibited a trend for association with eGFR ratio (r = 0.35, p = .07), over the same time period.

CONCLUSIONS

This urinary metabolite classifier can estimate MPA exposure and correlates with allograft inflammation. Future studies with larger samples are required to validate and evaluate its clinical application.

Noncompartmental pharmacokinetics of three intravenous mycophenolate mofetil concentrations in healthy Standardbred mares

BACKGROUND

Mycophenolate mofetil (MMF) is the prodrug of mycophenolic acid (MPA) which acts as an immunosuppressive agent. During the biotransformation of MMF to MPA, additional metabolites including MPA phenol glucuronide (MPAG), MPA acyl glucuronide (AcMPAG) and MPA phenol glucoside (MPG) are formed.

OBJECTIVE

To define the noncompartmental pharmacokinetic (PK) parameters of three single doses of intravenous (i.v.) MMF and its downstream metabolites in healthy horses.

ANIMALS

Six healthy Standardbred mares.

MATERIALS AND METHODS

Generic MMF (Par Pharmaceuticals; Chestnut Ridge, NY, USA) was reconstituted and administered as a single i.v. bolus at 1.0 mg/kg, 5.0 mg/kg and 10.0 mg/kg with an eight day washout between treatments. Blood samples were collected immediately before MMF administration and over 24 h. A liquid chromatography-tandem mass spectrometry assay was developed following FDA guidance to determine plasma MMF, MPA, MPAG, AcMPAG and MPG concentrations. Plasma concentrations were analysed independently, followed by calculation of geometric mean and coefficient of variation.

RESULTS

Noncompartmental PK parameters were determined for MMF and all metabolites at all doses. MMF was rapidly converted to MPA in all horses. Each incremental dose of MMF resulted in increases in C_max and AUC_inf _obs for MPA and the three additional metabolites. Within the 10-fold dose range, the increase in C_max and AUC_inf _obs for MMF and its metabolites was nonlinear.

CONCLUSIONS AND CLINICAL RELEVANCE

Horses biotransform MMF into MPA, MPAG, AcMPAG and MPG via the glucuronidation and glucosidation clearance pathways. Equine reference PK profiles for MPA and the metabolites, MPAG, AcMPAG and MPG were established.

Pharmacokinetics of free and total mycophenolic acid in paediatric and adult renal transplant recipients: Exploratory analysis of the effects of clinical factors and gene variants

Clinical and genetic influencing factors on free fraction of mycophenolic acid (MPA) have rarely been discussed. The present study investigated whether the clinical and genetic factors could explain the variability in the pharmacokinetics of free MPA (fMPA) and total MPA (tMPA) in Chinese paediatric and adult renal transplant recipients. Twenty-eight paediatric and 31 adult patients were enrolled, and the concentrations of tMPA and fMPA were determined at 0 h (predose) and 0.5, 1, 1.5, 2, 4, 5, 8, 9, 10 and 12 h after mycophenolate mofetil administration. Genetic polymorphisms of UGTs (rs671448, rs1042597, rs2741049, rs62298861, rs7439366, rs12233719) and ABCC2 (rs717620) were simultaneously determined. The clinical and genetic data were analysed and reported. tMPA and fMPA concentrations adjusted for dose per body weight were consistently higher in adults than in paediatric patients. In the paediatric group, only albumin and time after transplantation correlated significantly with the MPA-free fraction variation, which could explain 32.4% of the variability. Besides, ABCC2 polymorphism, albumin and time after transplantation correlated significantly with the MPA-free fraction variation in adults, which could explain 56.9% of the variability. The influencing factors in the paediatric group are different from those in adults, which may be due to age-related transporter expression.

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.

Pharmacokinetics of mycophenolate mofetil following single-dose intravenous and single- and multiple-dose oral administration and clinicopathologic effects of mycophenolate mofetil following long-term oral administration in healthy horses

OBJECTIVE

To characterize the pharmacokinetics of mycophenolate mofetil (MMF) following single-dose IV or PO administration, characterize the pharmacokinetics of MMF following long-term PO administration, and describe the clinicopathologic effects of long-term MMF administration in horses.

ANIMALS

12 healthy adult horses.

PROCEDURES

In phase 1, 6 horses received a single IV (2.5 mg/kg) or PO (5 mg/kg) dose of MMF in a randomized balanced crossover assessment (≥ 2-week interval between administrations). In phase 2, 6 other horses received MMF for 60 days (5 mg/kg, PO, q 24 h for 30 days and then 5 mg/kg, PO, q 48 h for an additional 30 days).

RESULTS

Following IV (single-dose) or PO (single- or multiple-dose) administration, MMF was rapidly converted to mycophenolic acid. For single-dose PO administration, mean ± SD maximum plasma mycophenolic acid concentration was 1,778.3 ± 441.5 ng/mL at 0.71 ± 0.29 hours. For single-dose IV administration, mean systemic clearance and volume of distribution at steady state were 0.689 ± 0.194 L/h/kg and 1.57 ± 0.626 L/kg, respectively. Following single doses, mean terminal half-life was 3.99 ± 0.865 hours for IV administration and 4.02 ± 1.01 hours for PO administration. The accumulation index following long-term PO administration was 1.0 ± 0.002, and the terminal half-life was 4.59 ± 1.25 hours following the final dose on day 60. None of the horses developed abnormal clinical signs or had any consistently abnormal clinicopathologic findings.

CONCLUSIONS AND CLINICAL RELEVANCE

Further investigation of the clinical efficacy of long-term MMF treatment of horses with autoimmune diseases is warranted.

The Application of Inosine 5'-Monophosphate Dehydrogenase Activity Determination in Peripheral Blood Mononuclear Cells for Monitoring Mycophenolate Mofetil Therapy in Children with Nephrotic Syndrome

In pediatric nephrotic syndrome, recommended mycophenolic acid (MPA) pharmacokinetics are higher than those for transplant recipients. In MPA therapeutic monitoring, inosine-5'-monophosphate dehydrogenase (IMPDH) activity may be useful. We modified the method established for renal transplant recipients and determined IMPDH activity in peripheral blood mononuclear cells (PBMCs) from healthy volunteers and children (4-16 years) with nephrotic syndrome treated with mycophenolate mofetil (MMF). From children, four blood samples were collected, and MPA concentrations were also determined. IMPDH activity was calculated using xanthosine monophosphate (XMP) normalized with adenosine monophosphate (AMP), both determined with the HPLC-UV method. The modified method was accurate, precise, and linear for AMP and XMP within 0.50-50.0 μmoL/L. Mean IMPDH activity in volunteers was 45.97 ± 6.24 µmoL·s^-1·moL^-1 AMP, whereas for children, the values were variable and amounted to 39.23 ± 27.40 µmoL·s^-1·moL^-1 AMP and 17.97 ± 15.24 µmoL·s^-1·moL^-1 AMP before the next MMF dose and 1 h afterward, respectively. The modified method may be applied to IMPDH activity determination in children with nephrotic syndrome treated with MMF. IMPDH activity should be determined after one thawing of PBMCs due to the change in AMP and XMP concentrations after subsequent thawing. For children, the lowest IMPDH activity was observed concomitantly with the highest MPA concentration.

Limited sampling strategy to predict mycophenolic acid area under the curve in pediatric patients with nephrotic syndrome: a retrospective cohort study

PURPOSE

Limited sampling strategy (LSS) is a precise and relatively convenient therapeutic drug monitoring method. We evaluated LSSs for mycophenolic acid (MPA) in children with nephrotic syndrome treated with mycophenolic mofetil (MMF) and validated the LSSs using two different approaches.

METHODS

We measured MPA plasma concentrations in 31 children using HPLC-UV method and received 37 MPA pharmacokinetic profiles (0-12 h). For six children, MPA profiles were estimated twice after two MMF doses. LSSs were developed using multilinear regression with STATISTICA and R software and validated using validation group and bootstrap method, respectively.

RESULTS

The best three time point equations included C₁, C₃, C₆ (good guess 83%, bias - 2.78%; 95% confidence interval (CI) - 9.85-0.46); C₁, C₂, C₆ (good guess 72%, bias 0.72%; 95% CI - 5.33-7.69); and C₁, C₂, C₄ (good guess 72%, bias 2.05%; 95% CI - 4.92-13.01) for STATISTICA software. For R software, the best equations consisted of C₁, C₃, C₆ (good guess 92%, bias - 2.69%; 95% CI - 27.18-33.75); C₀, C₁, C₃ (good guess 84%, bias - 2.11%; 95% CI - 24.19-22.29); and C₀, C₁, C₂ (good guess 84%, bias - 0.48%; 95% CI - 30.77-54.07). During validation, better results were obtained for R evaluations, i.e., bootstrap method.

CONCLUSIONS

The most useful equations included C₀, C₁, C₃ and C₀, C₁, C₂ time points; however, the most precise included C₁, C₃, C₆ time points because of MPA enterohepatic recirculation. Better results were obtained for bootstrap validation due to greater number of patients. Validated LSS should be used only in the population for which it was developed. As there is growing evidence that underexposure of MPA is associated with insufficient treatment response, we recommend the introduction of therapeutic drug monitoring for MPA in children with nephrotic syndrome.

Ex vivo binding of the immunosuppressant mycophenolic acid to dog and cat plasma proteins and the effect of co-incubated dexamethasone and prednisolone

Mycophenolic acid (MPA) has been shown to be promising for the treatment of autoimmune diseases in dogs and cats. In humans, MPA is highly bound to plasma proteins (~97%). It has been recommended to monitor free drug plasma concentrations because the free MPA correlates with its immunosuppressive effect. However, it is unknown if MPA is highly bound to plasma proteins in dogs and cats. The objectives of this study were to determine the extent of plasma protein binding of MPA and evaluate the effect of prednisolone and dexamethasone on the extent of protein binding of MPA in dogs and cats. The extent of plasma protein binding of MPA was determined in plasma collected from clinically healthy adult cats (n = 13) and dogs (n = 14) by combining high-throughput dialysis and ultra-high-liquid chromatography. This study reveals that MPA is highly bound to plasma proteins (>90%) in dogs and cats, mean extent of binding of MPA at 15 μg/ml to plasma proteins being 96% (range, 95%-97%) and 92% (range, 90%-93%) for dogs and cats, respectively. In dog plasma, MPA is primarily bound to albumin. In vitro, prednisolone increased the unbound MPA in dogs (p < .01) but not in cats (p = .07) while dexamethasone had no effect on MPA plasma binding in either species (p > .05). Results of this study provide valuable information for designing future pharmacokinetic and pharmacodynamic studies and also therapeutic monitoring programs for dogs and cats.

Pharmacokinetics of Mycophenolic Acid after Intravenous Administration of Mycophenolate Mofetil to Healthy Cats

Background

Mycophenolate mofetil (MMF), the prodrug of mycophenolic acid (MPA), is becoming increasingly popular as an alternative immunosuppressant in feline medicine. Pharmacokinetic information is not available for cats.

Objective

The purpose of this study was to determine whether MMF is biotransformed into the active metabolite MPA and to evaluate the disposition of MPA after a 2‐hour constant rate intravenous (IV) infusion of MMF in healthy cats.

Animals

Healthy cats (n = 6).

Methods

This was a prospective pilot study. All cats were administered MMF at 20 mg/kg every 12 hours over a 2‐hour constant rate infusion for 1 day. The concentrations of MPA and its derivatives in blood were determined using a validated UHPLC–UV method.

Results

All cats biotransformed MMF into MPA. The mean AUC_0‐14 h ranged from 6 to 50 h*mg/L after IV dosing of MMF. Transient large bowel diarrhea was recorded in 2 of 6 cats after medication administration.

Conclusion and Clinical Importance

The disposition of MPA in plasma was highly variable, which could result in high interindividual variability in the safety and efficacy of treatment with MMF in cats.

Dried Blood Spot sampling in psychiatry: Perspectives for improving therapeutic drug monitoring

Assessment of drug concentrations is indicated to guide dosing of a selected number of drugs used in psychiatry. Conventionally this is done by vena puncture. Novel sampling strategies such as dried blood spot (DBS) sampling have been developed for various drugs, including antipsychotics, antidepressants and mood-stabilizers. DBS sampling is typically performed by means of a finger prick. This method allows for remote sampling, which means that patients are not required to travel to a health care facility. The number of DBS assays for drugs used in psychiatry has increased over the last decade and includes antidepressants (tricyclic and serotonin and/or norepinephrine reuptake inhibitors), mood stabilizers and first- and second-generation antipsychotics. Available assays often comply with analytical validation criteria but are seldom used in routine clinical care. Little attention has been paid to the clinical validation and implementation processes of home sampling. Ideally, not only medicines but also clinical chemistry parameters should be measured within the same sample. This article reflects on the position of DBS remote sampling in psychiatry and provides insight in the requisites of making such a sampling tool successful.

Cost Evaluation of Dried Blood Spot Home Sampling as Compared to Conventional Sampling for Therapeutic Drug Monitoring in Children

Dried blood spot (DBS) sampling for the purpose of therapeutic drug monitoring can be an attractive alternative for conventional blood sampling, especially in children. This study aimed to compare all costs involved in conventional sampling versus DBS home sampling in two pediatric populations: renal transplant patients and hemato-oncology patients. Total costs were computed from a societal perspective by adding up healthcare cost, patient related costs and costs related to loss of productivity of the caregiver. Switching to DBS home sampling was associated with a cost reduction of 43% for hemato-oncology patients (€277 to €158) and 61% for nephrology patients (€259 to €102) from a societal perspective (total costs) per blood draw. From a healthcare perspective, costs reduced with 7% for hemato-oncology patients and with 21% for nephrology patients. Total savings depend on the number of hospital visits that can be avoided by using home sampling instead of conventional sampling.