Therapeutic monitoring of mycophenolate mofetil

Exploring the Impact of Pharmaceutical Excipient PEG400 on the Pharmacokinetics of Mycophenolic Acid Through In Vitro and In Vivo Experiments

Mycophenolic acid (MPA) is a commonly used immunosuppressant. In the human body, MPA is metabolized into mycophenolic acid 7-O-glucuronide (MPAG) and mycophenolic acid acyl-glucuronide (AcMPAG) mainly through liver glucuronidation, which involves UDP-glucuronosyltransferase (UGTs) and transfer proteins. Research has indicated that the pharmaceutical excipient PEG400 can impact drug processes in the body, potentially affecting the pharmacokinetics of MPA. Due to the narrow therapeutic window of MPA, combination therapy is often used, and PEG400 is widely used in pharmaceutical preparations. Therefore, investigating the pharmacokinetic influence of PEG400 on MPA could offer valuable insights for optimizing MPA's clinical use. In this study, we examined the impact of a single oral dose of PEG400 on the blood levels of MPA in rats through pharmacokinetic analysis. We also investigated the distribution of MPA in various tissues using mass spectrometry imaging. We explored the potential mechanism by which PEG400 affects the metabolism of MPA using hepatic and intestinal microsomes and the Caco-2 cellular transporter model. Our findings reveal that the overall plasma concentrations of MPA were elevated in rats following the co-administration of PEG400, with the AUC0-t of MPA and its metabolite MPAG increasing by 45.53% and 29.44%, respectively. Mass spectrometry imaging showed increased MPA content in tissues after PEG400 administration, with significant differences in the metabolites observed across different tissues. Microsomal and transport experiments showed that PEG400 accelerated the metabolism of MPA, promoted the uptake of MPA, and inhibited efflux. In conclusion, PEG400 alters the in vivo metabolism of MPA, potentially through the modulation of metabolic enzymes and transport.

Population pharmacokinetic analysis identifies an absorption process model for mycophenolic acid in patients with renal transplant

The pharmacokinetics (PKs) of mycophenolic acid (MPA) exhibit considerable complexity and large variability. We developed a population pharmacokinetic (popPK) model to predict the complex PK of MPA by examining an absorption model. Forty-two patients who had undergone renal transplantation were included in this study. popPK analysis, incorporating several absorption models, was performed using the nonlinear mixed-effects modeling program NONMEM. The MPA area under the concentration-time curve at 0-12 h (AUC0-12) was simulated using the final model to calculate the recommended dose. The PK of MPA was adequately described using a two-compartment model incorporating sequential zero- and first-order absorption with lag time. Total body weight, renal function (RF), and posttransplantation day (PTD) were included as covariates affecting MPA PK. The final model estimates were 7.56, 11.6 L/h, 104.0 L, 17.3 L/h, 169.0 L, 0.0453, 0.283, and 1.95 h for apparent nonrenal clearance, apparent renal clearance, apparent central volume of distribution, apparent intercompartmental clearance, apparent peripheral volume of distribution, absorption half-life, lag time, and duration of zero-order absorption, respectively. Simulation results showed that a dose regimen of 500-1000 mg twice daily is recommended during the early posttransplantation period. However, dose reduction could be required with increased PTD and decreased RF. The complex PK of MPA was explained using an absorption model. The developed popPK model can provide useful information regarding individual dosing regimens based on PTD and RF.

Quantification of Mycophenolic Acid in Plasma by High Performance Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Mycophenolate mofetil (MMF) and sodium mycophenolate are commonly prescribed immunosuppressive drugs for patients who have undergone solid organ transplant. Therapeutic drug monitoring (TDM) of these drugs is performed by assessing mycophenolic acid (MPA) in plasma. Due to the large inter-individual variability and narrow therapeutic range, the precise determination of systemic MPA concentration carries great clinical significance. We present a rapid, sensitive, specific, and robust liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantitation of MPA in plasma. A Waters Xevo TQ-S Micro mass spectrometer coupled to a Water's Acquity liquid chromatography system was used in positive electrospray ionization (ESI) mode. MPA quantitation was achieved using multiple reaction monitoring (MRM). Mycophenolic acid carboxybutoxy ether (MPAC) was employed as an internal standard. The method is linear from 0.25 to 40.00 mg/L, has intra-assay (N = 24) imprecision of 2.7% at 1.57 mg/L and 3.9% at 4.61 mg/L and inter-assay (N = 20 days) imprecision of 4.0% at 1.62 mg/L and 5.6% at 4.68 mg/L.

Pharmacokinetics and tolerability of multiple-day oral dosing of mycophenolate mofetil in healthy horses

BACKGROUND

Additional efficacious immunomodulatory treatment is needed for the management of immune-mediated disease in horses. Mycophenolate mofetil (MMF) is an immunosuppressive drug that warrants assessment as a viable therapeutic agent for horses.

HYPOTHESIS/OBJECTIVES

To evaluate the pharmacokinetics (PK) of multiple-day oral dosing of MMF in healthy horses and to determine the tolerability of this dosing regimen.

ANIMALS

Six healthy Standardbred mares.

METHODS

Horses received MMF 10 mg/kg PO q12h for 7 days in the fed state. Serial sampling was performed over 12 hours on Days 1 and 7 with trough samples collected every 24 hours, immediately before morning drug administration. Noncompartmental PK analyses were performed to determine primary PK parameters, followed by calculation of geometric means and coefficients of variation. A CBC, serum biochemical profile, physical examination, and fecal scoring were used to assess dose tolerability.

RESULTS

Seven days of treatment resulted in a mycophenolic acid (MPA) area under the curve (AUC0-12 ) of 12 594 h × ng/mL (8567-19 488 h × ng/mL) and terminal half-life (T1/2 ) of 11.3 hours (7.5-15.9 hours), yielding minor metabolite accumulation in all horses treated. Salmonellosis was detected in the feces of 2 horses by Day 7, and all horses developed myelosuppression, hyperbilirubinemia, hyporexia, decreased gastrointestinal motility, and decreased fecal output by the seventh day of treatment.

CONCLUSION AND CLINICAL IMPORTANCE

Administration of MMF at 10 mg/kg PO q12h resulted in hematologic and clinical toxicity within 1 week of treatment. A decreased MMF dose, frequency, or both is needed to avoid colic. Drug monitoring should include frequent hemograms, serum biochemical profiles, and strict biosecurity protocols.

The application of organ-on-chip models for the prediction of human pharmacokinetic profiles during drug development

Organ-on-chip (OoC) technology has led to in vitro models with many new possibilities compared to conventional in vitro and in vivo models. In this review, the potential of OoC models to improve the prediction of human oral bioavailability and intrinsic clearance is discussed, with a focus on the functionality of the models and the application in current drug development practice. Multi-OoC models demonstrating the application for pharmacokinetic (PK) studies are summarized and existing challenges are identified. Physiological parameters for a minimal viable platform of a multi-OoC model to study PK are provided, together with PK specific read-outs and recommendations for relevant reference compounds to validate the model. Finally, the translation to in vivo PK profiles is discussed, which will be required to routinely apply OoC models during drug development.

Development and application of a thin-film molecularly imprinted polymer for the measurement of mycophenolic acid in human plasma

BACKGROUND

Mycophenolic acid (MPA) is used to suppress the immune response following organ transplantation; however, complex pharmacokinetic behavior and a large interpersonal variability necessitate therapeutic drug monitoring. To overcome the limitations of current sample preparation techniques, we present a novel thin-film molecularly imprinted polymer (TF-MIP) extraction device as part of a simple, sensitive, and fast method for analysis of MPA from human plasma.

METHODS

Mycophenolic acid is extracted from plasma using a tailor-made TF-MIP that is subsequently desorbed into an organic solvent system compatible with mass spectrometry. The MIP yielded higher recovery of MPA relative to a corresponding non-imprinted polymer. The method allows for the determination of MPA in 45 min including analysis time and can be scaled for high throughput to process as many as 96 samples per hour.

RESULTS

The method gave an LOD of 0.3 ng mL^-1 and was linear from 5 to 250 ng mL^-1 . Patient plasma samples (35 μL) were diluted using charcoal-stripped pooled plasma to a final extraction volume of 700 μL; when MPA in patient plasma is high, this ratio can easily be adjusted to ensure samples are within the method linear range. Intra- and inter-day variability were 13.8% and 4.3% (at 15 ng mL^-1 ) and 13.5% and 11.0% (at 85 ng mL^-1 ), respectively (n = 3); inter-device variability was 9.6% (n = 10).

CONCLUSIONS

Low inter-device variability makes these devices suitable for single use in a clinical setting, and the fast and robust method is suitable for therapeutic drug monitoring, where throughput and time-to-result are critical.

Bronchiectasis in children following kidney transplantation in New Zealand

AIM

Bronchiectasis is an acquired chronic respiratory condition with a relatively high incidence in New Zealand children. Bronchiectasis following kidney transplant has been reported internationally. This study aimed to identify the incidence rate of bronchiectasis following paediatric kidney transplantation. Secondary aims were to assess the impact on kidney allograft function and identify risk factors that might prompt earlier diagnosis.

METHODS

Case control study of children who developed bronchiectasis following kidney transplant in New Zealand. All children who were transplanted during the 16-year period from 2001 to 2016 were included. Each identified case was matched with two controls (children who did not develop bronchiectasis and received a kidney transplant within the closest time period to their matched case). Data were collected on baseline demographics, clinical variables, immunosuppression and allograft function.

RESULTS

Of 95 children who had a kidney transplant during the specified time period, eight (8.4%) developed bronchiectasis at a median of 4 years post-transplant. The mean incidence rate of bronchiectasis was 526 cases per 100 000 paediatric kidney transplant population per year. The majority of children were Māori or Pasifika ethnicity and lived in areas of greater socio-economic deprivation. Immunosuppression burden and allograft function were not significantly different between groups.

CONCLUSIONS

The incidence rate of bronchiectasis following paediatric kidney transplantation is substantially higher than the baseline paediatric incidence rate in New Zealand. A high index of suspicion for bronchiectasis and prompt investigation of children post kidney transplantation with a history of recurrent lower respiratory tract infection or chronic cough are advised.

Low dose rabbit antithymocyte globulin is non-inferior to higher dose in low-risk pediatric kidney transplant recipients

BACKGROUND

Currently, there is no consensus among pediatric kidney transplant centers regarding the use and regimen for immunosuppressive induction therapy.

METHODS

In this single center, retrospective cohort study, pediatric kidney transplant recipients transplanted between 1 May 2013 and 1 May 2018 with rabbit antithymocyte globulin (rATG) induction were included. We stratified patients based on immunological risk, with high risk defined as those with repeat transplant, preformed donor specific antibody, current panel-reactive antibodies > 20%, 0 antigen match and/or African-American heritage. Outcome of interest was the incidence of biopsy proven acute rejection by 1 year.

RESULTS

A total of 166 patients met inclusion criteria. Age of patients was 12 years (11 mo-21 y), (median, range), 21.5% received a living donor transplant and 50.6% were female. Low-immunologic-risk patients were divided into 2 groups, those who received the lower cumulative rATG dose of ≤ 3.5 mg/kg (n = 52) versus the higher cumulative dose of > 3.5 mg/kg (n = 47). The median total dose in the lower dose group was 3.1 (IQR 0.3) and 4.4 (IQR 0.8) in the higher dose group, P < 0.001. Rejection rate did not differ significantly between the 2 treatment groups (7/52 vs. 6/47). None in the lower dose group developed BK nephropathy versus 3 in the higher dose group. Graft loss due to BK nephropathy occurred in 1 patient in the higher dose group. Graft loss in the whole cohort at 12 months was a rare event (n = 1) with 99.5% graft survival and 100% patient survival.

CONCLUSIONS

Reduced rATG dosing (≤ 3.5 mg/kg) when compared to higher dosing (> 3.5 mg/kg) is safe and effective in low-risk pediatric kidney transplant recipients without increasing risk of rejection. A higher resolution version of the Graphical abstract is available as Supplementary information.

Sustained suppression of enterohepatic circulation of mycophenolic acid by antimicrobial-associated diarrhea in a kidney transplant recipient with Crohn's disease: A case report

Mycophenolic acid (MPA) undergoes enterohepatic circulation. A kidney transplant patient on mycophenolate mofetil was treated with tazobactam/piperacillin for pyelonephritis, and developed antimicrobial-associated diarrhea. Consequently, the MPA trough level decreased by approximately 90%. Furthermore, it took approximately a month for the MPA level to normalize even after diarrhea had resolved.

Population Pharmacokinetics of Mycophenolic Acid in Renal Transplant Patients: A Comparison of the Early and Stable Posttransplant Stages

Mycophenolic acid (MPA) is an antimetabolic immunosuppressive drug widely used in solid organ transplantation and autoimmune diseases. Pharmacokinetics (PK) of MPA demonstrates high inter- and intra-variability. The aim of this study was to compare the population PK properties of MPA in adult renal transplant patients in the early and stable post-transplant stages and to simulate an optimal dosing regimen for patients at different stages. A total of 51 patients in the early post-transplant period (1 week after surgery) and 48 patients in the stable state (5.5–10 years after surgery) were included in the study. In the two-compartment population PK model, CL/F (23.36 L/h vs. 10.25 L/h) and V/F (78.07 vs. 16.24 L) were significantly different between the two stages. The dose-adjusted area under the concentration time curve (AUC_ss,12h/dose) for patients in the early stage were significantly lower than those for patients in the stable state (40.83 ± 22.26 mg h/L vs. 77.86 ± 21.34 mg h/L; p < 0.001). According to Monte Carlo simulations, patients with 1.0–1.5 g of mycophenolate mofetil twice daily in the early phase and 0.50–0.75 g twice daily in the stable phase had a high probability of achieving an AUC_ss,12h of 30–60 mg h/L. In addition, limited sampling strategies showed that two 4-point models (C0-C1-C2-C4 and C1-C2-C3-C6) performed well in predicting MPA exposure by both Bayesian estimate and regression equation and could be applied in clinical practice to assist therapeutic drug monitoring of MPA.

No Influence of Everolimus on Mycophenolic Acid Area Under the Concentration-Time Curve: Limited Sampling Strategy for Mycophenolic Acid in Japanese Kidney Transplant Recipients Treated With Tacrolimus, Mycophenolate Mofetil, Steroid, and Everolimus

BACKGROUND

Despite a growing need for everolimus (EVR) to reduce calcineurin inhibitor toxicity in kidney transplantation (KTx), the influence of EVR on the pharmacokinetics of mycophenolic acid (MPA), a mycophenolate mofetil (MMF) active metabolite, is obscure, and no suitable limited sampling strategy (LSS) for MPA when EVR is concomitantly present exists. We aimed to investigate the influence of EVR on MPA pharmacokinetics in KTx.

MATERIALS AND METHODS

This study complied with all principles of the Declaration of Helsinki. Twenty patients were initially administered tacrolimus, MMF, and methylprednisolone and then received EVR 4 months after KTx. Approximately 4 weeks before and after EVR administration, the estimated value of the area under the concentration-time curve for MPA from 0 to 12 hours (MPA-AUC0-12) was calculated using MPA blood concentration just before and 1, 2, 4, and 6 hours after MMF administration. We compared several MPA pharmacokinetics parameters before and after EVR addition and determined the best estimation equation for LSS of MPA-AUC0-12.

RESULTS

Although MPA-C6 per dose (MPA-C6/D) significantly decreased after EVR addition (from 3.4 [±2.2] ng/mL/g to 2.5 [±0.9] ng/mL/g), MPA-C0/D, -C1/D, -C2/D, -C4/D, and MPA-AUC0-12/D showed no significant change. MPA-AUC0-12/D did not correlate with EVR-AUC0-12/D. The best estimation equation for LSS of MPA-AUC0-12 by 2 time points was [(2.94 × C2) + (5.09 × C4) + 5.32] (R² = 0.73) and [(5.70 × C0) + (1.39 × C1) + 22.45] (R² = 0.72) before and after EVR addition, respectively.

CONCLUSIONS

EVR can be safely combined with MMF after KTx once our results have been reevaluated.

Immunomodulatory treatment of interstitial lung disease

Interstitial lung diseases (ILDs) other than idiopathic pulmonary fibrosis (IPF) have an array of immunomodulatory treatment options compared with IPF, due to their inflammatory component. However, there is a relative paucity of guidance on the management of this heterogeneous group of diseases. In ILDs other than IPF, immunosuppression is the cornerstone of therapy, with varying levels of evidence for different immunomodulatory agents and for each specific ILD. Classification of ILDs is important for guiding treatment decisions. Immunomodulatory agents mainly include corticosteroids, mycophenolate mofetil (MMF), azathioprine, methotrexate, cyclophosphamide and rituximab. In this review, the available evidence for single agents in the most common ILDs is first discussed. We then reviewed practical therapeutic approaches in connective tissue disease-related ILD and interstitial pneumonia with autoimmune features, scleroderma-related ILD, vasculitis and dermatomyositis with hypoxemic respiratory failure, idiopathic non-specific interstitial pneumonia, hypersensitivity pneumonitis sarcoidosis, fibrosing organizing pneumonia and eosinophilic pneumonia. The treatment of acute exacerbations of ILD is also discussed. Therapy augmentation in ILD is dictated by the recognition of progression of disease. Criteria for the evaluation of progression of disease are then discussed. Finally, specific protocol and measures to increase patients' safety are reviewed as well, including general monitoring and serologic surveillance, Pneumocystis jirovecii prophylaxis, patients' education, genetic testing for azathioprine, MMF serum levels and cyclophosphamide administration protocols. Immunomodulatory therapies are largely successful in the management of ILDs and can be safely managed with the application of specific protocols, precautions and monitoring.

New insights into the microbiome in kidney transplantation

PURPOSE OF REVIEW

Research in the past decade has revealed important implications for the microbiome in human health. Studies have defined a distinct gut microbiota in kidney transplant recipients and have recently linked the microbiota to infectious complications, similar to the allogeneic stem cell transplant population.

RECENT FINDINGS

In this review, we focus on the metabolism of immunosuppressive medications by the gut microbiota and on the urinary microbiome in the setting of infectious and immunological complications. We highlight seminal studies showing the role of specific gut microbiota in the direct metabolism of tacrolimus into a lesser effective immunosuppressant as well as the role of the gut microbiota in the metabolism of mycophenolic acid (MPA) glucuronide. We describe distinct urinary microbiota patterns in kidney transplant recipients with interstitial fibrosis tubular atrophy, chronic allograft nephropathy, tolerance, and bacterial and viral complications.

SUMMARY

The microbiota has important implications for immunosuppressive medications and immunological outcomes in kidney transplant recipients. Further research is needed to better delineate the impact of the metabolism of tacrolimus and MPA by gut bacteria and the role of the urine microbiota in the development of immunological and infectious complications.

Precision Medicine: Towards Individualized Dosing in Pediatric Rheumatology

Despite an increase in the number of available therapeutics, many children with rheumatic disease continue to experience active inflammatory disease and treatment failure. One reason for treatment failure is the lack of dosing paradigms to account for the wide between-patient variability in drug pharmacokinetics because of developmental changes or genetic polymorphisms that effect drug absorption, distribution, metabolism, and elimination. This review highlights several strategies to optimize dosing for biologic and nonbiologic disease-modifying antirheumatic drugs, including therapeutic drug monitoring, pharmacogenomics, and the use of pharmacokinetic/pharmacodynamic modeling.

Antiproliferatives and Transplantation

Antiproliferative agents include Mycophenolic acid and Azathioprine (which is less commonly used unless in certain conditions). They were initially identified for use in autoimmune and cancer research due to their role in disruption of cellular replication. They have now become the cornerstone of antirejection maintenance therapy in solid organ transplant. In this chapter we will describe the major times that lead to discovery, mechanisms of action, side effects, use during pregnancy and the major clinical trials.

Acute Mycophenolate Mofetil Overdose Managed Conservatively

Mycophenolate mofetil (MMF) is an immunosuppressant drug widely used in post-transplant patients and the treatment of various inflammatory conditions. It is considered a relatively safe drug with minimal adverse effects. We managed an acute overdose of 19 grams (g) of MMF with a suicidal intention in a 17-year-old female with no significant past medical history. Apart from episodes of mild headaches, she did not develop other symptoms, laboratory abnormalities, or complications.

A Limited Sampling Strategy for Therapeutic Drug Monitoring of Mycophenolate Mofetil for Prophylaxis of Acute Graft-Versus-Host Disease in Allogeneic Stem Cell Transplantation

A universally accepted strategy for therapeutic drug monitoring (TDM) of mycophenolate mofetil (MMF) in the prevention of acute graft-versus-host disease (aGVHD) in allogenic hematopoietic stem cell transplantation (alloHSCT) does not exist. We explored the feasibility of developing a limited sampling strategy (LSS) for TDM of MMF in this setting. Patients undergoing alloHSCT received standard MMF-cyclosporine prophylaxis, with MMF administered twice daily (BD) for matched transplant recipients or thrice daily (TID) in haploidentical transplantation. Intensive blood sampling was carried out on day 7 and area under the concentration–time curve (AUC) of mycophenolic acid (MPA), the active metabolite, was estimated using noncompartmental analysis. The ability of MPA exposure defined by AUC_0-12 to discriminate between responders (patients who did not develop GVHD) and nonresponders (patients who developed GVHD) was determined by receiver operating characteristic curve analysis. Patients were divided into training and validation sets within BD and TID groups. Mathematical equations were developed from the training set to predict AUC_0-12 from an abbreviated AUC involving a limited number of sampling points. The equations were validated in the validation set by comparing the MPA AUC_0-12 predicted from LSS with the observed AUC_0-12. It was observed that patients with AUC_0-12 ≤18.99 mg*h/L had a higher risk of developing aGVHD [odds ratio (OR) = 2.63 (1.17 to 5.87), P = 0.06]. The benefit was more in matched transplant recipients [OR = 3.5 (1.30 to 9.49), P = 0.05] as compared to haploindentical transplant [OR = 2.8 (0.49 to 15.91), P = NS]. Using the mathematical equations, the observed AUC_0-12 was predicted with 92.31% accuracy in the BD subset and 100% accuracy in the TID subset for a combined accuracy of 94.76%. A set of just three samples that constituted the abbreviated AUC_1-4 was used to develop the predictive models. The LSS could be employed for the therapeutic monitoring of MMF particularly in patients undergoing matched hematopoietic stem cell transplantation.

Gut microbiota profiles and fecal beta-glucuronidase activity in kidney transplant recipients with and without post-transplant diarrhea

Post-transplant diarrhea is a common complication after solid organ transplantation and is frequently attributed to the widely prescribed immunosuppressant mycophenolate mofetil (MMF). Given recent work identifying the relationship between MMF toxicity and gut bacterial β-glucuronidase activity, we evaluated the relationship between gut microbiota composition, fecal β-glucuronidase activity, and post-transplant diarrhea. We recruited 97 kidney transplant recipients and profiled the gut microbiota in 273 fecal specimens using 16S rRNA gene sequencing. We further characterized fecal β-glucuronidase activity in a subset of this cohort. Kidney transplant recipients with post-transplant diarrhea had decreased gut microbial diversity and decreased relative gut abundances of 12 genera when compared to those without post-transplant diarrhea (adjusted p value < .15, Wilcoxon rank sum test). Among the kidney transplant recipients with post-transplant diarrhea, those with higher fecal β-glucuronidase activity had a more prolonged course of diarrhea (≥7 days) compared to patients with lower fecal β-glucuronidase activity (91% vs 40%, p = .02, Fisher's exact test). Our data reveal post-transplant diarrhea as a complex phenomenon with decreased gut microbial diversity and commensal gut organisms. This study further links commensal bacterial metabolism with an important clinical outcome measure, suggesting fecal β-glucuronidase activity could be a novel biomarker for gastrointestinal-related MMF toxicity.

The use of mycophenolate mofetil area under the curve

PURPOSE OF REVIEW

Although mycophenolate mofetil (MMF) has been used successfully to treat a myriad of autoimmune diseases, its complex pharmacokinetics make it difficult to determine the true drug exposure for an individual patient. This review summarizes the body of literature focused on the gold standard measurement of the area under the curve (AUC) of mycophenolic acid (MPA), the active metabolite of MMF.

RECENT FINDINGS

Fixed dosing of MMF leads to highly variable drug exposure. Retrospective series have reported improved clinical outcomes when a minimum AUC value from 0 to 12 h (AUC0-12h) ≥30 mg h/l is achieved. MPA levels are affected by various drug interactions, hypoalbuminemia, and renal insufficiency and the measurement of free rather than total MPA levels is prudent in some situations. A limited number of studies employing prospective dose adjustment of MMF based on AUC0-12h measurements have yielded mixed results.

SUMMARY

Given the wide range of MPA AUC encountered in autoimmune diseases, dose adjustments of MMF based on AUC rather than fixed dosing of MMF should be considered in both clinical practice and clinical trials. Limited sampling strategies have been proposed to improve clinical feasibility of measurements, but a standard is yet to be defined.

The impact of omeprazole on mycophenolate pharmacokinetics in kidney transplant recipients

BACKGROUND

The absorption rates of mycophenolate mofetil (MMF) and enteric-coated mycophenolate sodium (EC-MPS) may be influenced by the concomitant use of omeprazole.

METHODS

One hundred kidney transplant patients were recruited during their outpatient visits, including 50 on MMF and 50 on EC-MPS. At the clinic, a predose mycophenolic acid (MPA) sample (C0) was collected; subsequently, the participants received the proton-pump inhibitor omeprazole along with either MMF or EC-MPS. Two more blood samples were collected at 1.5 and 3.5 hours and used to estimate an area under the curve (AUC) from zero to 12 hours [AUC (0-12)].

RESULTS

The mean number of months after transplant was 92 months. The median AUC (0-12) and C0 results were 62.2 mg·h/L and 2.0 mg/L for the MMF group and 71.9 mg·h/L and 1.8 mg/L for the EC-MPS group (P = 0.160 and 0.225, respectively). Interestingly, 54% of the MMF group and 62% of the EC-MPS group showed AUCs above the target values. The correlation between MPA C0 and the predicted AUC was poor in both groups.

CONCLUSION

Omeprazole can be safely co-administered with either MMF or EC-MPS, as it did not compromise the MPA exposure. Unexpectedly, however, a high percentage of patients presented MPA AUCs exceeding the target value, highlighting the importance of periodically assessing MPA level.

Lack of concordance between EMIT assay and LC-MS/MS for Therapeutic Drug Monitoring of Mycophenolic Acid: Potential increased risk for graft rejection?

Therapeutic drug monitoring (TDM) of immunosuppressive drugs is crucial in organ-transplanted patients to prevent rejection or toxic effects due to inadequate dosage. Mycophenolic acid (MPA) is a commonly used immunosuppressant in this setting. Nowadays, MPA concentrations are monitored by Enzyme Multiplied Immunoassay Technology (EMIT), and Liquid Chromatography (LC)-based techniques, particularly coupled to Tandem Mass Spectrometry (LC-MS/MS). This study evaluates the concordance between TDM results for MPA obtained through CE-IVD EMIT and LC-MS/MS assays in plasma samples. LC-MS/MS quantification was based on a commercial kit and the analytical performance in terms of accuracy was tested through external proficiency tests and inter-laboratory comparison with a home-made HPLC-UV method. Both these evaluations confirmed the reliability of the LC-MS/MS method (1.6 % and 9.0 % of bias, respectively). Conversely, the comparison between EMIT and LC-MS/MS showed overestimation by EMIT of 33.5 %. This bias resulted concentration-dependent, ranging from 46.4 % in the concentration range of 1-2 mg/L, to 21.4 % over 4 mg/L. Considering the theoretical clinical impact of this overestimation, a fraction comprised between 12.4 % and 31.4 % of samples which resulted over three different minimum effective concentration values by EMIT (no indication for dose adjustment) had discordant indications by LC-MS/MS (dose adjustment needed). Concluding, this study highlights a clinically relevant systematic overestimation of MPA concentration by EMIT, supporting the switch to LC-MS/MS techniques for TDM purpose. However, further prospective studies are needed in order to evaluate the clinical impact of switching the TDM activity from EMIT to LC-MS/MS in a larger cohort in a long period.

Recent advances in the management of non-infectious posterior uveitis

PURPOSE

To review the current regimens and novel therapeutic modalities in various stages of research and development for the management of non-infectious posterior uveitis (NIPU).

METHODS

We performed a thorough review of current literature using PubMed, Google Scholar and Clinicaltrials.gov to identify the published literature about the available therapeutics and novel drugs/therapies in different stages of clinical trials.

RESULTS

The current management regimen for non-infectious posterior uveitis includes corticosteroids, immunomodulatory therapies and anti-metabolites. However, NIPU requires long-term management for efficacious remission of the disease and to prevent disease relapse. Long-term safety issues associated with steroids have led to efforts to develop novel therapeutic agents including biological response modulators and immunosuppressants. The current therapeutic agents in various stages of development include calcineurin inhibitors, biologic response modifiers and a more a comprehensive modalities like ocular gene therapy as well as novel drug delivery mechanisms for higher bioavailability to the target tissues, with minimal systemic effects.

CONCLUSION

Novel efficacious therapeutic modalities under development will help overcome the challenges associated with the traditional therapeutic agents.

Pharmacodynamic assessment of mycophenolic acid in resting and activated target cell population during the first year after renal transplantation

Aims

To explore the pharmacodynamics of mycophenolic acid (MPA) through inosine monophosphate dehydrogenase (IMPDH) capacity measurement and purine levels in peripheral blood mononuclear cells (PBMC) longitudinally during the first year after renal transplantation (TX).

Methods

PBMC were isolated from renal recipients 0–4 days prior to and 6–9 days, 5–7 weeks and 1 year after TX (before and 1.5 hours after dose). IMPDH capacity and purine (guanine and adenine) levels were measured in stimulated and nonstimulated PBMC.

Results

Twenty‐nine patients completed the follow‐up period, of whom 24 received MPA. In stimulated PBMC, the IMPDH capacity (pmol 10⁻⁶ cells min⁻¹) was median (interquartile range) 127 (95.8–147) before TX and thereafter 44.9 (19.2–93.2) predose and 12.1 (4.64–23.6) 1.5 hours postdose across study days after TX. The corresponding IMPDH capacity in nonstimulated PBMC was 5.71 (3.79–6.93), 3.35 (2.31–5.62) and 2.71 (1.38–4.08), respectively. Predose IMPDH capacity in nonstimulated PBMC increased with time, reaching pre‐TX values at 1 year. In stimulated PBMC, both purines were reduced before (median 39% reduction across days after TX) and after (69% reduction) dose compared to before TX. No alteration in the purine levels was observed in nonstimulated PBMC. Patients needing dose reductions during the first year had lower pre‐dose IMPDH capacity in nonstimulated PBMC (1.87 vs 3.00 pmol 10⁻⁶ cells min⁻¹, P = .049) at 6–9 days.

Conclusion

The inhibitory effect of MPA was stronger in stimulated PBMC. Nonstimulated PBMC became less sensitive to MPA during the first year after TX. Early IMPDH capacity appeared to be predictive of dose reductions.

Impact of SLCO1B3 polymorphisms on clinical outcomes in lung allograft recipients receiving mycophenolic acid

Single-nucleotide polymorphisms (SNPs) in genes involved in mycophenolic acid (MPA) metabolism have been shown to contribute to variable MPA exposure, but their clinical effects are unclear. We aimed to determine if SNPs in key genes in MPA metabolism affect outcomes after lung transplantation. We performed a retrospective cohort study of 275 lung transplant recipients, 228 receiving mycophenolic acid and a control group of 47 receiving azathioprine. Six SNPs known to regulate MPA exposure from the SLCO, UGT and MRP2 families were genotyped. Primary outcome was 1-year survival. Secondary outcomes were 3-year survival, nonminimal (≥A2 or B2) acute rejection, and chronic lung allograft dysfunction (CLAD). Statistical analyses included time-to-event Kaplan-Meier with log-rank test and Cox regression modeling. We found that SLCO1B3 SNPs rs4149117 and rs7311358 were associated with decreased 1-year survival [rs7311358 HR 7.76 (1.37-44.04), p = 0.021; rs4149117 HR 7.28 (1.27-41.78), p = 0.026], increased risk for nonminimal acute rejection [rs4149117 TT334/T334G: OR 2.01 (1.06-3.81), p = 0.031; rs7311358 GG699/G699A: OR 2.18 (1.13-4.21) p = 0.019] and lower survival through 3 years for MPA patients but not for azathioprine patients. MPA carriers of either SLCO1B3 SNP had shorter survival after CLAD diagnosis (rs4149117 p = 0.048, rs7311358 p = 0.023). For the MPA patients, Cox regression modeling demonstrated that both SNPs remained independent risk factors for death. We conclude that hypofunctional SNPs in the SLCO1B3 gene are associated with an increased risk for acute rejection and allograft failure in lung transplant recipients treated with MPA.

The utility of trough mycophenolic acid levels for the management of lupus nephritis

Background

Monitoring of mycophenolic acid (MPA) levels may be useful for effective mycophenolate mofetil (MMF) dosing. However, whether commonly obtained trough levels are an acceptable method of surveillance remains debatable. We hypothesized that trough levels of MPA would be a poor predictor of area under the curve (AUC) for MPA.

Methods

A total of 51 patients with lupus nephritis who were on MMF 1500 mg twice a day and had a 4-h AUC done were included in this study. MPA levels were measured prior to (C0) and at 1 (C1), 2 (C2) and 4 (C4) h, followed by 1500 mg of MMF. The MPA AUC values were calculated using the linear trapezoidal rule. Regression analysis was used to examine the relationship between the MPA trough and AUC. Differences in the MPA trough and AUC between different clinical and demographic categories were compared using t-tests.

Results

When grouped by tertiles there was significant overlap in MPA, AUC 0-4 and MPA trough in all tertiles. Although there was a statistically significant correlation between MPA trough levels and AUC, this association was weak and accounted for only 30% of the variability in MPA trough levels. This relationship might be even more unreliable in men than women. The use of angiotensin-converting enzyme inhibitors or angiotensin receptor blockers was associated with increased MPA trough levels and AUC at 0-4 h (AUC0-4).

Conclusion

Trough levels of MPA do not show a strong correlation with AUC. In clinical situations where MPA levels are essential to guide therapy, an AUC0-4 would be a better indicator of the adequacy of treatment.

Optimizing Mycophenolic Acid Exposure in Kidney Transplant Recipients: Time for Target Concentration Intervention

The immunosuppressive agent mycophenolate is used extensively in kidney transplantation, yet dosing strategy applied varies markedly from fixed dosing ("one-dose-fits-all"), to mycophenolic acid (MPA) trough concentration monitoring, to dose optimization to an MPA exposure target (as area under the concentration-time curve [MPA AUC0-12]). This relates in part to inconsistent results in prospective trials of concentration-controlled dosing (CCD). In this review, the totality of evidence supporting mycophenolate CCD is examined: pharmacological characteristics, observational data linking exposure to efficacy and toxicities, and randomized controlled trials of CCD, with attention to dose optimization method and exposure achieved. Fixed dosing of mycophenolate consistently leads to underexposure associated with rejection, as well as overexposure associated with toxicities. When CCD is driven by pharmacokinetic calculation to a target concentration (target concentration intervention), MPA exposure is successfully controlled and clinical benefits are seen. There remains a need for consensus on practical aspects of mycophenolate target concentration intervention in contemporary tacrolimus-containing regimens and future research to define maintenance phase exposure targets. However, given ongoing consequences of both overimmunosuppression and underimmunosuppression in kidney transplantation, impacting short- and long-term outcomes, these should be a priority. The imprecise "one-dose-fits-all" approach should be replaced by the clinically proven MPA target concentration strategy.

Adverse effects of mycophenolic acid in renal transplant recipients: gender differences

Background Mycophenolic acid is widely used immunosuppressive drug, associated with adverse effects which increase patient morbidity and decrease medication adherence. Objective To evaluate the adverse effects in renal transplant recipients under mycophenolate treatment with respect to gender. Setting University Clinical Centre of Nis, Clinic of Nephrology, Serbia. Method This research included 96 renal transplant recipients, who received immunosuppressive regimen, based on tacrolimus or cyclosporin A, prednisone and mycophenolic acid. The high-performance liquid chromatography method combined with protein precipitation was used for the analysis of mycophelate concentration in human plasma. Drug concentration and dose-adjusted concentration were determined with respect to the patients' gender. An adverse effect scoring system developed by nephrologists within the University of Buffalo Nephrology/Transplant Program was used to monitor adverse effects of therapy. Main outcome measure Individual and scores of adverse effects in relation to the dosing regimen and gender. Results Results showed statistically lower dose and concentrations in men compared to the women in our investigation group. Also, female patients demonstrated higher mean scores (cumulative and subscores) within the same dosing regimens of mycophenolic acid. The gastrointestinal score was significantly higher in women who received a dose greater than 720 mg compared to men (0.20 ± 0.12 vs 0.12 ± 0.12). Women demonstrated higher individual adverse effects such as diarrhea and skin changes (41.7 vs 17.0; p = 0.038 and 62.5 vs 30.2; p = 0.037, respectively). Conclusions The results of our research showed that recipients' gender may play an important role in pharmacokinetic profile of mycophenolic acid, suggesting that women had higher concentration of mycophenolic acid and more serious side effects.

Pharmacokinetic Drug-Drug Interactions Between Letermovir and the Immunosuppressants Cyclosporine, Tacrolimus, Sirolimus, and Mycophenolate Mofetil

Letermovir (AIC246, MK-8228) is a human cytomegalovirus terminase inhibitor indicated for the prophylaxis of cytomegalovirus infection and disease in allogeneic hematopoietic stem cell transplant recipients that is also being investigated for use in other transplant settings. Many transplant patients receive immunosuppressant drugs, of which several have narrow therapeutic ranges. There is a potential for the coadministration of letermovir with these agents, and any potential effect on their pharmacokinetics (PK) must be understood. Five phase 1 trials were conducted in 73 healthy female participants to evaluate the effect of letermovir on the PK of cyclosporine, tacrolimus, sirolimus, and mycophenolic acid (active metabolite of mycophenolate mofetil [MMF]), as well as the effect of cyclosporine and MMF on letermovir PK. Safety and tolerability were also assessed. Coadministration of letermovir with cyclosporine, tacrolimus, and sirolimus resulted in 1.7-, 2.4-, and 3.4-fold increases in area under the plasma concentration-time curve and 1.1-, 1.6-, and 2.8-fold increases in maximum plasma concentration, respectively, of the immunosuppressants. Coadministration of letermovir and MMF had no meaningful effect on the PK of mycophenolic acid. Coadministration with cyclosporine increased letermovir area under the plasma concentration-time curve by 2.1-fold and maximum plasma concentration by 1.5-fold, while coadministration with MMF did not meaningfully affect the PK of letermovir. Given the increased exposures of cyclosporine, tacrolimus, and sirolimus, frequent monitoring of concentrations should be performed during administration and at discontinuation of letermovir, with dose adjustment as needed. These data support the reduction in clinical dosage of letermovir (to 240 mg) upon coadministration with cyclosporine.

RELATE: Relationship of limited sampling strategy and adverse effects of mycophenolate mofetil in pediatric renal transplant patients

MMF, a prodrug converted to the active form MPA, is an immunosuppressant used to prevent rejection in solid organ transplant recipients. MPA exposure, defined by AUC, can be estimated using limited sampling strategies (LSS). The relationship between MPA AUC and clinical outcomes has not been studied in pediatrics. The objectives were to describe the relationship of MPA AUC (estimated via LSS) with adverse effects and rates of rejection, and to compare clinical outcomes between different MPA monitoring practices. Descriptive statistics were used to summarize demographics, adverse effects, and rejection. Thirty-three patients (91 trough concentrations and 12 LSS sets) aged 2-20 years old were included. The estimated median MPA AUCs (David-Neto and Filler) were higher for those who did not have any adverse effects reported (65.85 and 85.05 mg*h/L, respectively) compared to those who had an adverse effect (60.75 and 54.2 mg*h/L, respectively). The median trough concentration when no adverse effects occurred was comparable to when adverse effects occurred. The median MPA AUC at which rejection occurred was lower than in those without rejection. The median trough concentration at which rejection occurred was higher than those without rejection (3.1 mg/L compared to 1.9 mg/L). The occurrence of adverse effects or rejection was not shown to be related to measured MPA trough or AUC outside of the target therapeutic range. The value of MPA concentration monitoring remains unclear; therefore, the practice of monitoring MPA AUC by LSS or trough concentrations should be reconsidered.

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.

Causes of Hemoptysis in Renal Transplant Patients

OBJECTIVES

Hemoptysis is a symptom that can be caused by airway disease, pulmonary parenchymal disease, or pulmonary vascular disease, or it can be idiopathic. Infection is the most common cause of hemoptysis, accounting for 60% to 70% of cases. Hemoptysis is also an initial symptom of diffuse alveolar hemorrhage syndrome, although it may be absent at presentation in one-third of patients. Diffuse alveolar hemorrhage is characterized by disruption of the alveolar-capillary basement membranes because of either injury or inflammation of the arterioles, venules, or capillaries, resulting in bleeding in alveolar spaces. To date, no study in the literature has investigated the cause of hemoptysis in renal transplant patients. In this retrospective study, we aimed to investigate the causes of hemoptysis in renal recipients.

MATERIALS AND METHODS

The data included in this study were obtained from 352 renal transplant patients who were consulted by the pulmonology department regarding hemoptysis between 2011 and 2017 at Baskent University. Patient medical records were reviewed for demographic, clinical, radiographic, bronchoscopic features, and microbiology data. Immunosuppressive drugs and clinical outcome data were also noted.

RESULTS

This study included 352 renal transplant patients (139 male patients with mean age of 34.9 ± 7 years and 113 female patients with mean age of 31.1 ± 5 years). Hemoptysis was detected in 17 patients (4.8%),with 3 (0.85%) having massive hemoptysis as a result of diffuse alveolar hemorrhage syndrome. Fourteen of our patient group (4%) had pneumonia, and Aspergillus species was detected in 5 patients (1.4%). The only reason for diffuse alveolar hemorrhage was immunosuppressive agents, including sirolimus and mycophenolate mofetil.

CONCLUSIONS

Hemoptysis is an important respiratory symptom in renal transplant patients. Although community- or hospital-acquired pneumonia may result in hemoptysis, drug-induced diffuse alveolar hemorrhage and Aspergillus infection should be considered for causes in renal transplant patients.

Fatal visceral disseminated varicella zoster infection during initial remission induction therapy in a patient with lupus nephritis and rheumatoid arthritis-possible association with mycophenolate mofetil and high-dose glucocorticoid therapy: a case report

BACKGROUND

Visceral disseminated varicella zoster viral (VZV) infection is a rare but severe complication with a high mortality rate in immunosuppressed individuals, and an increased susceptibility to VZV has been reported in kidney transplant recipients who are treated with mycophenolate mofetil (MMF). In Japan, MMF is currently approved for patients with lupus nephritis (LN) and data to indicate its optimal dosage are still insufficient.

CASE PRESENTATION

A 46-year-old Japanese woman with rheumatoid arthritis was diagnosed as having systemic lupus erythematosus (SLE) and LN class III (A/C). Although initial remission-induction therapy with prednisolone and tacrolimus was started, her serum creatinine level and urinary protein excretion were elevated. Methylprednisolone pulse therapy was added, and tacrolimus was switched to MMF. Two months after admission when she was taking 40 mg of PSL and 1500 mg of MMF daily, she suddenly developed upper abdominal pain and multiple skin blisters, and disseminated visceral VZV infection was diagnosed. Laboratory examinations demonstrated rapid exacerbation of severe acute liver failure and coagulation abnormalities despite immediate multidisciplinary treatment, and she died of hemorrhagic shock 7 days after the onset of abdominal pain. A serum sample collected at the time of admission revealed that she had recursive VZV infection.

CONCLUSIONS

MMF together with high-dose glucocorticoid therapy may increase the risk of VZV infection in Asian patients with SLE. Accumulation of evidence for parameters of safety, such as the area under the blood concentration-time curve of mycophenolic acid, should be urgently considered in order to establish a safer protocol for remission induction therapy in Asian patients with LN.

Increased Exposure of Tacrolimus by Co-administered Mycophenolate Mofetil: Population Pharmacokinetic Analysis in Healthy Volunteers

The objective of the study was to investigate the pharmacokinetic drug-drug interactions between tacrolimus (TAC) and mycophenolate mofetil (MMF) in healthy Korean male volunteers. Seventeen volunteers participated in a three-period, single-dose, and fixed sequence study. They sequentially received MMF, TAC, and the combination. Concentrations of TAC, mycophenolic acid (MPA), and its metabolites MPA 7-O-glucuronide and MPA acyl glucuronide were measured. The variants of CYP3A4, CYP3A5, SLCO1B1, SLCO1B3, ABCC2, UGT1A9, and UGT2B7 were genotyped. Drug interaction was evaluated with a non-compartmental analysis and population pharmacokinetic modelling to quantify the interaction effect. A total of 1,082 concentrations of those analytes were analysed. AUC_0-inf of TAC increased by 22.1% (322.4 ± 174.1 to 393.6 ± 121.7 ng·h/mL; P < 0.05) when co-administered with MMF, whereas the pharmacokinetic parameters of MPA and its metabolites were not changed by TAC. Apparent clearance (CL/F) of TAC was 17.8 L/h [relative standard error (RSE) 11%] or 13.8 L/h (RSE 11%) without or with MMF, respectively. Interaction was explained by the exponential model. The CYP3A5 genotype was the only significant covariate. The population estimate of CL/F of TAC was 1.48-fold (RSE 16%) in CYP3A5 expressers when compared to nonexpressers. CL/F of TAC was decreased when co-administered with MMF in these subjects.

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.

Pharmacokinetic Variability of Mycophenolic Acid in Pediatric and Adult Patients With Hematopoietic Stem Cell Transplantation

The aim of this study was to evaluate the pharmacokinetic variations of mycophenolic acid (MPA), the active metabolite of mycophenolate mofetil (MMF), in both pediatric and adult patients following hematopoietic stem cell transplantation (HSCT). Twenty pediatric patients with a median age of 3 years (range 0.2-12 years) and 13 adult patients with a median age of 54 years (range 18-63 years) were enrolled. Blood samples were collected on days 0, 7, 14, 21, and 30 after allogeneic HSCT. Total and free (unbound) MPA as well as MPA 7-O-glucuronide (MPAG) were quantified using a validated LC-MS/MS assay. The plasma protein binding of MPA and MPAG did not change significantly in pediatric patients over the 1-month sampling period post-HSCT. However, it increased in adult patients from day 7 to day 30 post-HSCT, from 97.3 ± 0.8% to 98.3 ± 0.6% for MPA (P < .05), and 74.6 ± 9.4% to 82.9 ± 8.1% for MPAG (P < .05). The plasma protein binding of MPA was significantly higher in males compared to females in both pediatric (98.3 ± 1.1% vs 97.4 ± 1.1%) and adult (98.1 ± 0.7% vs 97.4 ± 1.2%) patients (P < .05). The MPAG/MPA ratios on a milligram-per-kilogram dose basis in adult patients were significantly higher than those in pediatric patients (4.3 ± 3.4 vs 2.4 ± 2.6; P < .05). Time-dependent plasma protein binding and age-related differences in MPA metabolism at least in part impact the reported large intra- and interindividual variability in MPA pharmacokinetics. These patient and pharmacologic factors, if incorporated into MMF regimen design and modification, may contribute to the rational dose selection of MMF in HSCT patients.

Clinical Pharmacokinetics of Mycophenolic Acid in Hematopoietic Stem Cell Transplantation Recipients

Mycophenolate mofetil (MMF), an ester prodrug of mycophenolic acid (MPA), is widely used as a maintenance immunosuppressive regimen in solid organ transplant patients. It is increasingly used for the prophylaxis and treatment of graft-versus-host disease (GVHD) in hematopoietic stem cell transplantation (HSCT) patients. MPA displays extensive binding to serum albumin and glucuronidation to the inactive MPA-7-O-glucuronide (MPAG). Here, we review and discuss the pertinent information regarding the clinical pharmacokinetics of MPA in HSCT patients. The pharmacokinetics of MPA are altered in HSCT patients with lower oral bioavailability, shorter half-life and higher clearance than those in healthy volunteers and renal transplant recipients. Moreover, clearance may be increased in young pediatric patients. The optimal MMF dosing and preferred targets are still under investigation in HSCT patients due to the substantial intra- and inter-individual pharmacokinetic variability of MPA and broad range of transplants (malignant vs. nonmalignant, related vs. unrelated donor, and human leukocyte antigen mismatch). The complex pharmacokinetics of MPA have partly hampered the efficient use of MMF, and pharmacokinetic studies in HSCT patients have been limited in size and mostly inconclusive. Future research should be multi-institutional and focus on developing clinical decisions with adequate statistical power to improve clinical care of HSCT recipients.

Usefulness of limited sampling strategy for mycophenolic acid area under the curve considering postoperative days in living-donor renal transplant recipients with concomitant prolonged-release tacrolimus

Background

The optimal dose of mycophenolate mofetil (MMF) in renal transplant patients has been recommended to be decided on the basis of area under the concentration-time curve (AUC_0-12) of mycophenolic acid (MPA). Although meta-analysis has revealed that postoperative day (POD) is an influencing factor in MPA pharmacokinetics, there are no reports regarding a limited sampling strategy (LSS) for MPA AUC in consideration of POD. The aim of this study was to construct of an LSS considering POD that appropriately expresses the MPA AUC following renal transplantation and evaluation of the usefulness.

Methods

Serum concentration–time profiles (measured AUC_0-12) comprising nine sampling points over 12 h were analyzed in 36 living-donor renal transplant recipients after MMF administration with concomitant once-daily prolonged-release tacrolimus. Two LSSs were developed by stepwise multiple regression analysis (Method A: not classified by PODs; Method B: classified by PODs into POD < 31 and POD ≥ 31). Each LSS comprised four blood-sampling points within 6 h after MMF administration. Precision and reliability were verified by using root-mean-square error (RMSE), correlation coefficient (R²), and coefficient of determination (q²) by using leave-one-out cross-validation. The absolute values of the difference between measured and estimated AUCs (delta AUC) were compared for both estimating equations.

Results

One-hundred samples obtained from 36 recipients for AUC_0-12 comprised POD < 31 (n = 39) and POD ≥ 31 (n = 61). Estimation of AUC_0-12 by Method B resulted in better accuracy and reliability (Method A: RMSE = 5.5, R² = 0.85, q² = 0.83; Method B: POD < 31: RMSE = 5.5, R² = 0.86, q² = 0.83; POD ≥ 31: RMSE = 3.9, R² = 0.92, q² = 0.89) and significantly lower median delta AUC compared with that by Method A (delta AUC: 2.6 (0.0–11.6) v.s. 3.9 (0.1–18.1), p = 0.032).

Conclusion

These results suggest that LSS, classified as POD < 31 or POD > 31, would provide more accurate and reliable estimation of MPA AUC_0-12 in Japanese living-donor renal transplant patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s40780-017-0086-7) contains supplementary material, which is available to authorized users.

Unusual Case of Acute Lung Injury in a Renal Allograft Recipient

A renal allograft recipient developed cough with hemoptysis on the 1^st postoperative day. A chest X-ray was performed which was suggestive of fluid overload. His fluid was restricted and diuretics were added. On the same day, his pulmonary infiltrates worsened and a computed tomography (CT) of the chest was carried out, which was suggestive of the right lower lobe consolidation and left pleural effusion. He underwent a bronchoscopy and the lavage was sent for cultures, which did not grow any infective organism. Besides routine antibiotics, treatment for possible cytomegalovirus, fungal infections, and pneumocystis infection was instituted. Noninvasive ventilation was started on day 8. A repeat CT of the chest on the postoperative day 8 showed further worsening of the pulmonary infiltrates. As all the initial cultures and serology were negative, a possibility of interstitial pneumonitis was considered. Mycophenolate sodium was considered as a possible cause of the lung infiltrates and was withdrawn. The patient showed progressive improvement. His antibiotics were withdrawn. He was discharged on day 14. A repeat CT 4 weeks post transplant showed significant improvement in his pulmonary pathology. The acute lung injury was considered to be a drug reaction secondary to mycophenolate sodium. In a renal allograft recipient with persistent pulmonary infiltrates, interstitial involvement secondary to drugs should be considered if the patient does not improve with the standard treatment measures.

LC-MS/MS method for quantitation of mycophenolic acid, mycophenolic acid acyl-glucuronide, and 7-O-mycophenolic acid glucuronide in serum

Mycophenolic acid (MPA) is the active metabolite of the immunosuppressant drug mycophenolate mofetil (MMF), which is commonly prescribed after organ transplantation in conjunction with other immunosuppressants. MMF therapy is monitored to balance therapeutic efficacy with minimizing adverse effects associated with high serum concentrations. A LC-MS/MS method was developed for the quantification of MPA and two additional metabolites, 7-O-mycophenolic acid glucuronide (MPAG) and mycophenolic acid acyl-glucuronide (AcMPAG), in serum using reverse-phase chromatography and multiple reaction monitoring (MRM) in positive electrospray ionization mode. Analytes were chromatographically resolved and the method was linear from 0.5 to 30.0 µg/ml MPA, 4.7 to 300 µg/ml MPAG, and from 0.5 to 30.0 µg/ml AcMPAG. Calibration curves for all analytes had r ≥ 0.990. Intra- and inter-assay imprecision coefficients of variation (CVs) were ≤6.9% and ≤14.5%, respectively. No ion suppression or interferences were observed. The method compared favorably with an unaffiliated reference laboratory. Retrospective data analyses indicate interpatient differences in drug metabolism.

Therapeutic Drug Monitoring of Mycophenolic Acid

Mycophenolic acid (MPA) is an immunosuppressant requiring therapeutic drug monitoring. Although immunoassays are commercially available, there is significant positive bias using this approach when compared to high-performance liquid chromatography or LC combined with mass spectrometry (LC/MS) or tandem mass spectrometry (LC/MS/MS). Positive bias is due to variable cross-reactivity of MPA acyl glucuronide with antibodies traditionally used in immunoassay formats. As can be expected, the magnitude of bias varies considerably. MPA strongly binds albumin and, as a result, disproportionate increases in free MPA occur in patients with uremia, hypoalbuminemia, and hepatic dysfunction. As such, monitoring free MPA poses additional challenges. Because MPA inhibits inosine monophosphate dehydrogenase, monitoring this enzyme may provide an alternative approach.

In Vitro Influence of Mycophenolic Acid on Selected Parameters of Stimulated Peripheral Canine Lymphocytes

Mycophenolic acid (MPA) is an active metabolite of mycophenolate mofetil, a new immunosuppressive drug effective in the treatment of canine autoimmune diseases. The impact of MPA on immunity is ambiguous and its influence on the canine immune system is unknown. The aim of the study was to determine markers of changes in stimulated peripheral canine lymphocytes after treatment with MPA in vitro. Twenty nine healthy dogs were studied. Phenotypic and functional analysis of lymphocytes was performed on peripheral blood mononuclear cells cultured with mitogens and different MPA concentrations– 1 μM (10⁻³ mol/m³), 10 μM or 100 μM. Apoptotic cells were detected by Annexin V and 7-aminoactinomycin D (7-AAD). The expression of antigens (CD3, CD4, CD8, CD21, CD25, forkhead box P3 [FoxP3] and proliferating cell nuclear antigen [PCNA]) was assessed with monoclonal antibodies. The proliferation indices were analyzed in carboxyfluorescein diacetate succinimidyl ester (CFSE)-labeled cells. All analyses were performed using flow cytometry. The influence of MPA on apoptosis was dependent on the mechanism of cell activation and MPA concentration. MPA caused a decrease in the expression of lymphocyte surface antigens, CD3, CD8 and CD25. Its impact on the expression of CD4 and CD21 was negligible. Its negative influence on the expression of FoxP3 was dependent on cell stimulation. MPA inhibited lymphocyte proliferation. In conclusion, MPA inhibited the activity of stimulated canine lymphocytes by blocking lymphocyte activation and proliferation. The influence of MPA on the development of immune tolerance–expansion of Treg cells and lymphocyte apoptosis–was ambiguous and was dependent on the mechanism of cellular activation. The concentration that MPA reaches in the blood may lead to inhibition of the functions of the canine immune system. The applied panel of markers can be used for evaluation of the effects of immunosuppressive compounds in the dog.

Implications of Clinical Mycophenolate Mofetil Dose According to Individual Body Weight in Japanese Renal Transplant Recipients

BACKGROUND

Mycophenolate mofetil (MMF) is generally administered at a fixed dose of 0.5-1.5 g/d without considering individual body weight (BW) in Japanese renal transplant outpatients receiving maintenance therapy. We aimed to investigate the implications of the area under the curve of mycophenolic acid (MPA AUC):MMF dose ratio by individual BW and suggest the index of MMF dose according to individual BW.

METHODS

Forty-three Japanese patients who received a renal transplant ≥6 months before the study were enrolled. Blood samples were collected at 4 time points: at predose, 20 minutes, 1 hour, and 3 hours after MMF administration.

RESULTS

The mean ± standard deviation MMF dose, MPA AUC, and BW of all patients were 581 ± 207 mg/d, 36.2 ± 18.7 μg·h/mL, and 56.3 ± 11.1 kg, respectively. Patients with a lower BW tended to have a higher MPA AUC:MMF dose ratio than patients with a higher BW. There was a significant correlation between the MMF dose:BW ratios and MPA AUC (r(2) = 0.330; P < .01). The rate of MPA AUC between 30 and 60 μg·h/mL with the MMF dose:BW ratio of 10-16 mg/kg was 73.7%.

CONCLUSION

Individual BW seems to affect the MPA AUC:MMF dose ratio; therefore, we need to consider individual BW when deciding on a MMF dose. The MMF dose:BW ratio of 10-16 mg/kg could predict MPA AUC between 30 and 60 μg·h/mL with a probability of approximately 75%. Therefore, it could be a useful index for outpatients, because it is difficult to draw blood frequently from such patients.

Use of Glucuronidated Mycophenolic Acid Levels for Therapeutic Monitoring in Pediatric Lupus Nephritis Patients

BACKGROUND/OBJECTIVES

Mycophenolate mofetil (MMF) is used to treat pediatric-onset lupus nephritis (pLN). Data are equivocal on the use of plasma mycophenolic acid (MPA) levels as a measure of efficacy and predictor of therapeutic outcomes in pLN. Glucuronidated MPA (MPA-G) is an inactive metabolite that is a marker of adequate absorption and normal metabolism of MMF. We evaluated the use of MPA and MPA-G levels in routine care of pLN.

METHODS

This was a retrospective study of pLN patients treated with MMF dosed at 600 mg/m. Clinical renal remission (CR) was defined as proteinuria of less than 500 mg/24 h. Midinterval MPA and MPA-G plasma levels were drawn during routine follow-up, approximately 6 hours after the previous dose of MMF. Steady-state levels of MPA were calculated using pharmacokinetics and compared with routine midinterval plasma MPA levels.

RESULTS

Seventeen pLN patients treated with MMF had MPA and MPA-G levels. Eleven patients were in CR; 6 were not in CR at the time of evaluation and had not responded to MMF after more than 3 months of therapy. The mean MPA level for patients in CR was 3.26 ± 2.02 μg/mL compared with 3.02 ± 1.76 μg/mL for patients not in CR. Three patients in CR did not have detectable levels of MPA. Calculated steady-state levels of MPA did not reflect the observed levels. Glucuronidated MPA levels were therapeutic (44.2 ± 26.7 μg/mL) in patients in CR, but low (29.88 ± 22 μg/mL) in patients not in CR (not statistically significant).

CONCLUSIONS

Midinterval plasma levels of MPA do not reflect predicted steady-state levels in pLN and do not correlate with clinical response. Midinterval plasma levels of MPA-G indicate adequate absorption and may correlate better with clinical pLN activity.