Mycophenolic Acid Concentrations Research Articles

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.

Population pharmacokinetics of mycophenolic acid in adult kidney transplant patients under prednisone and tacrolimus regimen

Mycophenolate mofetil (MMF) is typically used in combination with prednisone and tacrolimus to avoid graft rejection in kidney transplant patients. The aim of this study was to develop and validate a population pharmacokinetic model of mycophenolic acid (MPA) in kidney transplant patients to investigate the influence of clinical and genetic covariates and to propose a dosage regimen based on the final model. Adult kidney transplant patients (>18 years old) receiving combination of MMF, prednisone and tacrolimus regimen were included. The population pharmacokinetic model was built using a two-compartment model and First Order Conditional Estimation method with Interaction (FOCEI though NONMEM v.7.4.). A total of 343 MPA concentrations at steady state from 77 kidney transplant patients were included in the analysis. MPA CL/F, V1/F, Q/F, V2/F, and Ka were 12.4 L/h, 45.6 L, 29.9 L/h, 658 L, and 1.67 h−1, respectively. It was found that CL/F increases with serum creatinine and uric acid levels and V1/F is modified by blood urea nitrogen and the UGT1A9 genotype. In the final model the interindividual variabilities associated to CL/F and V1/F were 56.5% and 105.8%, respectively. The residual variability was 41.8%. Evaluation by bootstrapping showed that the final model was stable. The predictive performance was evaluated by goodness-of-fit plots and visual predictive check. Dosage regimens for MMF were proposed based on the final model and would be appropriate for a prospective evaluation. In conclusion, it was built a population pharmacokinetic model for MPA in kidney transplant patients, which include clinical and genetic covariates.

Assessment of Mycophenolic Acid Levels on Biopsy Proven Rejection and Adverse Effects in Pediatric Heart Transplant Recipients

Therapeutic ranges of Mycophenolic Acid (MPA) concentrations have not been established in pediatric heart transplant recipients. There are limited data supporting are under the concentration-time curve (AUC) in adult heart transplant on outcomes such as rejection, but AUC monitoring may be not be feasible in clinical practice. The purpose of our study is to evaluate the relationship between mycophenolic acid (MPA) trough levels and incidence of biopsy proven rejection and adverse effects in pediatric heart transplant patients. A single-center retrospective chart review was performed on patients receiving heart transplant between Jan 2011 and Dec 2015. Patients included for analysis were ≤18 years at transplant and received maintenance immunosuppression with tacrolimus, mycophenolate, and a corticosteroid. Endomyocardial biopsy grades up to one-year post transplant and simultaneous MPA levels were recorded. Patients with acute cellular rejection scores of 2R or 3R or immunopathologic evidence of antibody mediated rejection were considered as biopsy proven acute rejection (BPAR). Leukopenia, gastrointestinal side effects, and mycophenolate dose decreases were also recorded. A total of 47 patients were included in the final analysis. There were no significant differences in baseline demographics between patients who had BPAR and those who did not. Overall 24% of patients had at least 1 incidence of BPAR after heart transplant. The mean MPA trough levels between the group of patients with rejection (2.4 ug/mL +/- 1.62) and those without rejection (2.46 ug/mL +/- 1.74) was not significantly different (p=0.38). Mean MPA trough levels also were also not consistent when examining rejection by time from transplant. Only examining by individual MPA trough levels on biopsy days did we observe a significantly lower MPA trough 1.6 ug/mL +/- 1.05 in those with rejection versus those without 2.5 ug/mL +/- 1.69 (p=0.02). The mean MPA level associated with a dose decrease due to an adverse effect between these two groups was not significant. MPA trough levels may have a relationship with incidence of biopsy proven rejection or with incidence of adverse events within one-year post transplant in this population. Controlled prospective studies with are warranted to further evaluate this potential relationship.

PETINIA法による血中ミコフェノール酸測定試薬の基準測定法LC-MS/MS法との比較

PETINIA法による血中ミコフェノール酸測定試薬の基準測定法LC-MS/MS法との比較

Development and validation of an ultra-performance liquid chromatography mass spectrometry/mass spectrometry method for simultaneous quantification of total and free mycophenolic acid and its metabolites in human plasma.

A reliable method has been validated using ultra-performance liquid chromatography mass spectrometry (MS)/MS for simultaneous evaluation of human plasma concentration of mycophenolic acid (MPA) and its major metabolites both total and free form. All analytes were extracted from plasma by simple protein precipitation procedure with methanol. Samples for determination of their free form concentration require a preanalytic spin through an ultrafiltration system. The chromatographic separation was completed using C18column at 0.3 ml/min with a gradient condition. Method validation was performed as the United State Food and Drug Administration guidelines for bio-analytical methods concerning precision, accuracy, linearity, selectivity, recovery, and matrix effect. Linearity was obtained over concentration of 0.05–4, 0.5–60, and 0.025–3 μg/ml for total MPA, mycophenolic acid glucuronide (MPAG) and mycophenolic acid acyl-glucuronide (AcMPAG), respectively. The linearity of the method for free form of analytes was confirmed in the range of 10–500, 125–10,000, and 0.5–300 ng/ml for MPA, MPAG, and AcMPAG, respectively. The intra- and interday accuracy ranged from 85.73%–102.01% for total form, and 87.23%–111.89% for free form, and the precisions of all analytes were lower than 15%. The mean recoveries of the analytes ranged from 85.54% to 94.76% and the matrix factor ranged from 0.88–1.06. The developed method is rapid, sensitive and convenient for pharmacokinetic study or therapeutic drug monitoring in patients after oral administration of enteric-coated mycophenolate sodium or mycophenolate mofetil.

Mycophenolic Acid and Its Pharmacokinetic Drug-Drug Interactions in Humans: Review of the Evidence and Clinical Implications.

Mycophenolic acid (MPA) is an immunosuppressive agent commonly prescribed during posttransplant periods for the prevention of acute and chronic rejection following organ transplantation. Compelling evidence has demonstrated a pivotal role of the exposure level of MPA in determining the rate of allograft rejection as well as the incidence of adverse outcomes, such as gastrointestinal complaints and myelosuppression. Because MPA has wide interindividual pharmacokinetic (PK) variability, the importance of maintaining the MPA concentration levels within its therapeutic range is clear. In addition, due to its complex PKs, MPA is prone to inadvertently develop PK drug-drug interactions (DDIs) with many agents, some of which are commonly used in organ transplant recipients. Failure to acknowledge such clinically significant PK DDIs between MPA and other coadministered drugs could potentially lead to devastating outcomes, ie, the occurrence of acute and chronic allograft rejection or the development of severe adverse events. The rationale to avoid concomitant use of certain drugs with MPA has been established; however, there is a lack of comprehensive literature to guide clinicians and medical professionals on the recognition and monitoring of potential PK DDIs when MPA is prescribed. In this article we comprehensively review, summarize, and discuss previous clinical studies that investigated the impact of coadministered drugs on the PK of MPA, with a major focus on the PK DDIs between MPA and commonly coadministered drugs.

Salting-out liquid–liquid microextraction to the determination of mycophenolic acid in plasma samples

This study aimed to develop a determination method of mycophenolic acid (MPA) in biological samples using salting-out liquid–liquid microextraction from human plasma samples based on the formation of a fluorescent complex with terbium ion and its application in quantification of the MPA in clinical samples. MPA extracted from plasma samples by salting-out liquid–liquid microextraction after protein precipitation by acetonitrile. Then, the fluorescence intensity was measured at 545 nm using an excitation wavelength of 347 nm after optimization of extraction parameters. Under the optimum conditions for the developed method, it provided a linear range between 0.5 and 5.0 µg/mL with a correlation coefficient (R2) of 0.998, and then, the validation was performed according to the FDA guideline and the developed method could quantify MPA concentration in real plasma samples. The results showed that linearity, accuracy, and precision of the developed analysis method were suitable for the determination of the MPA in plasma samples.

Plasmapheresis Reduces Mycophenolic Acid Concentration: A Study of Full AUC0-12 in Kidney Transplant Recipients.

Background: Mycophenolic acid (MPA), a crucial immunosuppressive drug, and plasmapheresis, an effective immunoreduction method, are simultaneously used for the management of various immune-related diseases, including kidney transplantation. While plasmapheresis has been proven efficient in removing many substances from the blood, its effect on MPA plasma levels remains unestablished. Objectives: To evaluate the full pharmacokinetics of MPA by measuring the area under the time–concentration curve (AUC0–12), which is the best indicator for MPA treatment monitoring after each plasmapheresis session, and to compare the AUC0–12 measurements on the day with and on the day without plasmapheresis. Methods: A cross-sectional study was conducted in kidney transplantation recipients who were taking a twice-daily oral dose of mycophenolate mofetil (MMF, Cellcept®) and undergoing plasmapheresis at King Chulalongkorn Memorial Hospital, Bangkok, Thailand, during January 2018 and January 2019. The MPA levels were measured by an enzymatic method (Roche diagnostic®) 0, 1/2, 1, 2, 3, 4, 6, 8, and 12 h after MMF administration, for AUC0–12 calculation on the day with and on the day without plasmapheresis sessions. Plasmapheresis was started within 4 h after administering the oral morning dose of MMF. Our primary outcome was the difference of AUC0–12 between the day with and the day without plasmapheresis. Results: Forty complete AUC measurements included 20 measurements on the plasmapheresis day and other 20 measurements on the day without plasmapheresis in six kidney transplant patients. The mean age of the patients was 56.2 ± 20.7 years. All patients had received 1000 mg/day of MMF for at least 72 h before undergoing 3.5 ± 1.2 plasmapheresis sessions. The mean AUC on the day with plasmapheresis was lower than that on the day without plasmapheresis (28.22 ± 8.21 vs. 36.79 ± 10.29 mg × h/L, p = 0.001), and the percentage of AUC reduction was 19.49 ± 24.83%. This was mainly the result of a decrease in AUC0–4 of MPA (23.96 ± 28.12% reduction). Conclusions: Plasmapheresis significantly reduces the level of full AUC0–12 of MPA. The present study is the first to measure the full AUC0–12 in MPA-treated patients undergoing plasmapheresis. Our study suggests that a supplementary dose of MPA is necessary for patients undergoing plasmapheresis.

The pharmacokinetics of mycophenolic acid in rats with orotic acid induced nonalcoholic fatty liver disease.

Post-transplantation nonalcoholic fatty liver disease (NAFLD) is common in liver transplant recipients. Changes in the expression levels and activities of drug-metabolizing enzymes and drug transporters have been reported in patients with NAFLD and relevant rodent models. Here, we evaluated whether the pharmacokinetics of mycophenolic acid (MPA), an immunosuppressant, would be altered in rats with NAFLD. NAFLD was induced by feeding a diet containing 1% (w/w) orotic acid for 20 days. The extent of hepatic glucuronidation of MPA to a major metabolite, mycophenolic acid-7-O-glucuronide (MPAG), did not differ between rats with NAFLD and controls. The expression levels of hepatic multidrug resistance-associated protein 2, responsible for biliary excretion of MPAG, were comparable in rats with NAFLD and controls; the biliary excretion of MPAG was also similar in the two groups. Compared with control rats, rats with NAFLD did not exhibit significant changes in the areas under the plasma concentration - time curves of MPA or MPAG after intravenous (5 mg/kg) or oral (10 mg/kg) administration of MPA. However, delayed oral absorption of MPA was observed in rats with NAFLD compared with controls; the MPA and MPAG peak plasma concentrations fell significantly and the times to achieve them were prolonged following oral administration of MPA.

Investigation of the Association Between Total and Free Plasma and Saliva Mycophenolic Acid Concentrations Following Administration of Enteric-Coated Mycophenolate Sodium in Adult Kidney Transplant Recipients.

Mycophenolic acid (MPA) is commonly used following renal transplant. Saliva MPA concentrations may reflect the pharmacologically active form of MPA in plasma. Therapeutic drug monitoring using saliva is convenient and non-invasive. This study examined the correlation between total and free plasma and saliva MPA concentrations following enteric-coated mycophenolate sodium (EC-MS) administration in renal transplant recipients. Total and free plasma and saliva MPA concentrations were measured simultaneously in 20 adult renal transplant recipients 1-2months' post-transplant. Thirteen samples were taken pre-dose and at specified time points up until 12h post-dose. When considering all time points, correlation between total plasma and saliva MPA was r2 = 0.51 and between free plasma and saliva MPA concentrations r2 = 0.41. The correlation between total plasma MPA area under the concentration-time curve (AUC) or free plasma AUC and saliva MPA AUC was r2 = 0.25 and r2 = 0.13, respectively. The correlation between total plasma MPA AUC and total plasma MPA trough (C0) concentrations was r2 = 0.51, and between total plasma MPA AUC and saliva MPA trough concentrations, r2 = 0.03. Measurement of MPA concentration in saliva cannot currently replace plasma measurement for therapeutic drug monitoring of MPA following EC-MS administration. Additional studies are required to examine the relationship between MPA saliva concentrations and patient outcomes.

Limited Sampling Strategy for the Estimation of Mycophenolic Acid and its Acyl Glucuronide Metabolite Area under the Concentration-Time Curve in Japanese Lung Transplant Recipients.

The dose of mycophenolate mofetil (MMF) used to prevent rejection after lung transplantation is often adjusted based on the 12-hour area under the concentration-time curve (AUC0-12) of mycophenolic acid (MPA). A limited sampling strategy (LSS) is useful to define the pharmacokinetic (PK) profiles of MPA and mycophenolic acid acyl glucuronide (AcMPAG). Therefore, this study aimed to design a LSS based on multiple linear regression for estimating the AUC0-12 of MPA and AcMPAG at the minimum blood sampling points in Japanese lung transplant patients with concomitant tacrolimus. Forty-five lung transplantation recipients were enrolled in a PK study of MPA, mycophenolic acid glucuronide (MPAG), and AcMPAG. The plasma MPA, MPAG, and AcMPAG concentrations were determined just before and at 0.5, 1, 2, 4, 8, and 12 hours after dosing. The AUC0-12 of MPA and AcMPAG was calculated using a linear trapezoidal rule from the plasma concentration of each blood sampling time. LSS was used to develop models for estimated AUC in the model group (n = 23) and was evaluated in the validation group (n = 22). The best three time-point equation was 4.04 + 1.64·C1 + 3.08·C4 + 5.17·C8 for MPA, and -0.13 + 3.01·C1 + 3.51·C4 + 5.74·C8 for AcMPAG. The prediction errors (PE) and the absolute prediction errors (APE) were within the clinically acceptable ± 5% and 15% range, respectively (MPA: PE = 2.00%, APE = 11.66%, AcMPAG: PE = 0.98%, APE = 14.69%). The percentage of estimated AUC0-12 within ± 15% of the observed AUC0-12 was 77.27% for MPA and 81.82% for AcMPAG. LSS using three time-point (C1, C4, and C8) provides the most reliable and accurate simultaneous estimation of the AUC0-12 of MPA and AcMPAG in Japanese lung transplant patients.

Pharmacokinetics of mycophenolic acid and its effect on CD4+ and CD8+ T cells after oral administration of mycophenolate mofetil to healthy cats.

BackgroundMycophenolate mofetil (MMF) is an immunosuppressant used in human and veterinary medicine. Little pharmacokinetic and pharmacodynamic information on MMF is available in cats.ObjectiveTo evaluate the plasma disposition of mycophenolic acid (MPA) and assess its effect on total peripheral blood mononuclear cells and CD4+/CD8+ ratios after PO administration of MMF.AnimalsHealthy cats (n = 10).MethodsMycophenolate mofetil was administered at a dosage of 10 mg/kg q12h (n = 3), 15 mg/kg q12h (n = 3), and 15 mg/kg q8h (n = 4) for 7 days. Concentrations of MPA and derivatives were determined using ultra‐high‐performance liquid chromatography. Flow cytometry was used to assess CD4+/CD8+ T‐cell ratios.ResultsAll cats biotransformed MMF into MPA. Half of the cats (5/10) had adverse effects within 1 week of MMF administration. Area under the curve limit of quantification (AUC0‐LOQh) of MPA ranged from 1.27 to 2.03 hours·μg/mL and from 1.77 to 8.54 hours·μg/mL after the first and last PO dose of 10 mg/kg. The AUC0‐loqh of MPA ranged from 2.18 to 31 hours·μg/mL after the first dose of 15 mg/kg of MMF. Before the first dose of MMF, the average total number of PBMC ranged from 1.2 to 9.3 million/mL. At the last dose of MMF, the average total number of PBMC ranged from 3 to 5 million/mL.ConclusionMycophenolic acid was detected in all cats. The dose 10 mg/kg given q12h for 1 week was tolerated (n = 3). The efficacy of MMF as an immunosuppressant and long‐term safety in cats of this dosage regimen is unknown.

Model based development of tacrolimus dosing algorithm considering CYP3A5 genotypes and mycophenolate mofetil drug interaction in stable kidney transplant recipients

This study quantifies the interaction between tacrolimus (TAC) and mycophenolate mofetil (MMF) in kidney transplant recipients. Concentrations of TAC, mycophenolic acid (MPA), and metabolites were analyzed and relevant genotypes were determined from 32 patients. A population model was developed to estimate the effect of interaction. Concentrations of TAC were simulated in clinical scenarios and dose-adjusted trough concentrations per dose (C/D) were compared. Effect of interaction was described as the inverse exponential relationship. Major determinants of trough levels of TAC were CYP3A5 genotype and interaction with MPA. The absolute difference in C/D of TAC according to co-administered MMF was higher in CYP3A5 non-expressers (0.55 ng/mL) than in CYP3A5 expressers (0.35 ng/mL). The effect of MMF in determining the TAC exposure is more pronounced in CYP3A5 non-expressers. Based on population pharmacokinetic model, we suggest the TAC dosing algorithm considering the effects of CYP3A5 and MMF drug interaction in stable kidney transplant recipients.

Effects of an Ex Vivo Pediatric Extracorporeal Membrane Oxygenation Circuit on the Sequestration of Mycophenolate Mofetil, Tacrolimus, Hydromorphone, and Fentanyl.

With the expanding use of extracorporeal membrane oxygenation (ECMO), understanding drug pharmacokinetics has become increasingly important, particularly in pediatric patients. This ex vivo study examines the effect of a pediatric Quadrox-iD ECMO circuit on the sequestration and binding of mycophenolate mofetil (MMF), tacrolimus, and hydromorphone hydrochloride, which have not been extensively studied to date in pediatric ECMO circuits. Fentanyl, which has been well studied, was used as a comparator. ECMO circuits were set up using Quadrox-iD pediatric oxygenators and centrifugal pumps. The circuit was primed with whole blood and a reservoir was attached to represent a 5-kg patient. Fourteen French venous and 12 French arterial ECMO cannulas were inserted into the sealed reservoir. Temperature, pH, PO2, and PCO2 were monitored and corrected. MMF, tacrolimus, hydromorphone, and fentanyl were injected into the ECMO circuit. Serial blood samples were taken from a postoxygenator site at intervals over 12 hours, and levels were measured. Hydromorphone hydrochloride was not as significantly sequestered by the ex vivo pediatric ECMO circuit when compared with fentanyl. Both mycophenolic acid and tacrolimus serum concentrations were stable in the circuit over 12 hours. Hydromorphone may represent a useful medication for pain control for pediatric patients on ECMO due to its minimal sequestration. Mycophenolic acid and tacrolimus also did not show significant sequestration in the circuit, which was unexpected given their lipophilicity and protein-binding characteristics, but may provide insight into unexplored pharmacokinetics of particular medications in ECMO circuits.

Pharmacokinetics of Enteric-Coated Mycophenolate Sodium in Lupus Nephritis (POEMSLUN).

Background:Mycophenolate mofetil or enteric-coated mycophenolate sodium (EC-MPS) and steroids are used for induction and maintenance therapy in severe lupus nephritis. Blood concentrations of mycophenolic acid (MPA), the active metabolite of these drugs, vary among patients with lupus nephritis. The objective of this study was to examine whether concentration-controlled (CC) dosing (through therapeutic drug monitoring) of EC-MPS results in a higher proportion of participants achieving target exposure of MPA compared with fixed-dosing (FD). An additional aim of the study was to evaluate the influence of CC dosing on clinical outcomes.Methods:Nineteen participants were randomly assigned either to the FD or CC group. All the participants were eligible to have free and total measurements of MPA over a period of 8–12 hours on 3 different occasions. Area under the concentration–time curve between 0 and 12 hours (AUC0-12) was calculated using noncompartmental methods. Dose of EC-MPS was titrated according to AUC0-12 in the CC group.Results:Thirty-two AUC0-12 measurements were obtained from 9 FD and 9 CC participants. Large inter-patient variability was observed in both groups but was more pronounced in the FD group. There were no significant differences between FD and CC participants in any pharmacokinetic parameters across the study visits, except for total C0 (FD 2.0 ± 0.3 mg/L versus CC 1.1 ± 0.3; P = 0.01) and dose-normalized C0 (FD 2.9 ± 0.2 mg/L/g versus CC 2.1 ± 0.7 mg/L/g; P = 0.04) at the second visit and total AUC0-12 (FD 66.6 ± 6.0 mg·h/L versus CC 35.2 ± 11.4 mg·h/L; P = 0.03) at the third visit. At the first study visit, 33.3% of the FD and 11.1% of the CC participants achieved the target area under the concentration–time curve (P = 0.58). From the second visit, none of the FD participants, compared with all the CC participants, achieved target AUC0-12 (P = 0.01). More CC participants achieved remission compared with FD participants (absolute difference of −22.2, 95% confidence interval 0.19 to 0.55; P = 0.62). The mean free MPA AUC0-12 was significantly lower in those who had complete remission.Conclusions:CC participants reached target AUC0-12 quicker. Larger studies are required to test clinical efficacy.

High plasma mycophenolate acid concentration in the early phase of induction therapy predicts good renal outcome in lupus nephritis

Objectives: To identify the prognostic predictive factor of complete renal response (CR) at week 12 by focusing on the plasma mycophenolic acid (MPA) concentration in induction therapy in lupus nephritis.Methods: We prospectively enrolled patients with biopsy-proven LN class III/IV who were hospitalized between 2016 and 2017. As an induction therapy, mycophenolate mofetil was continuously introduced at 2000 mg/day. We measured the MPA plasma concentration at two time points depending on the induction therapy phase, early (week 4) or middle (week 12). The association between these concentrations and CR rate at week 12 was evaluated.Results: Ten patients were enrolled. A significantly higher AUC0–12 between 0 and 12 h of MPA at the early phase was observed in the patients with CR at week 12 than in those without (p = .03). All the patients with high MPA-AUC0–12 (> 40 mg h/L) at the early phase achieved CR at week 12, but no such association was found at the middle phase. The multivariate analysis revealed that MPA-AUC0–12 was selected as an independent predictive factor of CR at week 12 (odds ratio: 1.12; 95% confidence interval: 1.01–1.45, p = .02).Conclusion: The high AUC0–12 of MPA at the early phase of induction therapy may predict good renal response.

A multiple methods approach to determine adherence with prescribed mycophenolate in children with kidney transplant.

The aim of this study was, to use a multiple methods approach, including, for the first time, dried blood spot (DBS) sampling with population pharmacokinetic interpretation, to assess adherence to mycophenolate in children with kidney transplant. A second aim was to identify patient/parental factors that influenced adherence and to link adherence behaviour to clinical outcomes. A convenience sample of 33 children with kidney transplant (age≤18years) who had been prescribed mycophenolate for at least 3months were recruited from participating outpatient clinics in the UK and Jordan. Medication adherence was determined via self-report questionnaires, medication refill data from dispensing records, and via mycophenolic acid concentrations in plasma and DBS samples obtained from children during a clinic visit. Through triangulation of results from the different methodological approaches a total of 12 children (36.4%) were deemed to be nonadherent with their prescribed mycophenolate treatment. Logistic regression analysis indicated that nonadherence was significantly associated with the presence of mycophenolate side effects. Poor adherence was positively linked to measures of poor clinical outcomes (hospitalisation and the need for kidney biopsy). Despite the imperative regarding medication adherence to help prevent organ rejection, a significant proportion of children are not fully adherent with their therapy. Side-effects appear to be an important factor leading to nonadherence. Measurement of mycophenolate in DBS samples, coupled with the use of population pharmacokinetics modelling, was a convenient direct approach to assessing adherence in children with kidney transplant and has the potential to be introduced into routine practice.

Development and validation of a sensitive liquid-chromatography tandem mass spectrometry assay for mycophenolic acid and metabolites in HepaRG cell culture: Characterization of metabolism interactions between p-cresol and mycophenolic acid.

Mycophenolic acid (MPA), a frequently used immunosuppressant, exhibits large inter-patient pharmacokinetic variability. This study (a) developed and validated a sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for MPA and metabolites [MPA glucuronide (MPAG) and acyl-glucuronide (AcMPAG)] in the culture medium of HepaRG cells; and (b) characterized the metabolism interaction between MPA and p-cresol (a common uremic toxin) in this in vitro model as a potential mechanism of pharmacokinetic variability. Chromatographic separation was achieved with a C18 column (4.6 × 250 mm,5 μm) using a gradient elution with water and methanol (with 0.1% formic acid and 2 mm ammonium acetate). A dual ion source ionization mode with positive multiple reaction monitoring was utilized. Multiple reaction monitoring mass transitions (m/z) were: MPA (320.95 → 207.05), MPAG (514.10 → 303.20) and AcMPAG (514.10 → 207.05). MPA-d3 (323.95 → 210.15) and MPAG-d3 (517.00 → 306.10) were utilized as internal standards. The calibration curves were linear from 0.00467 to 3.2 μg/mL for MPA/MPAG and from 0.00467 to 0.1 μg/mL for AcMPAG. The assay was validated based on industry standards. p-Cresol inhibited MPA glucuronidation (IC50 ≈ 55 μm) and increased MPA concentration (up to >2-fold) at physiologically relevant substrate-inhibitor concentrations (n = 3). Our findings suggested that fluctuations in p-cresol concentrations might be in part responsible for the large pharmacokinetic variability observed for MPA in the clinic.

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 theadverse effects in renal transplant recipients under mycophenolatetreatment 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 regimensof mycophenolic acid. The gastrointestinal score was significantly higher in women who received a dose greater than 720mg 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.

Mycophenolic Acid Area under the Curve Monitoring via Limited Sampling Strategy in Pediatric Heart Transplant Recipients

Purpose The study aim was to investigate exposure to mycophenolic acid (MPA), the active metabolite of mycophenolate mofetil (MMF), after pediatric orthotopic heart transplantation (pOHT). Previous studies in pediatric kidney recipients demonstrated a relationship between MPA concentration and risk of rejection or hematologic side effects. The quantification of MPA in pOHT is not well established, and the relationship between a single-time-point-correlate and area under the curve (AUC) is lacking. We sought to assess the clinical individualization of MPA dosing after initiation of MPA AUC measurements in our patients. Methods Between April 2017 and September 2018, 81 pOHT were performed, from which 22 AUCs in 14 patients were collected via a 3 point limited sampling strategy. Indication for MPA measurement, MMF dose, frequency of dosage adjustment, and time from transplant were examined via retrospective chart review. The first year post pOHT biopsies are for concern of rejection based on frequent echocardiograms, or per DSAs, monitored at transplant and months 3, 6, and 12 thereafter. Results Median MPA AUC was 37.5 mg*h/L (range 14-216) at 61 days post-pOHT (range 11-4426). Median patient age was 10 years (range 46 days-16 years). Of 22 MPA AUCs collected, 12 warranted dosage adjustments for optimization. Within those, 9 patients' AUCs were re-measured post adjustment with 8 attaining goal range 30-60 mg*h/L. Median MMF dose was 500 mg/m^2, or 18.8 mg/kg, both twice daily. Fifty percent of all AUCs were for-cause indications: high-risk Epstein-Barr Virus donor positive, recipient negative (n=4); high-risk Cytomegalovirus donor positive, recipient negative (n=2); recent infections requiring systemic antimicrobials (n=4); and diagnosis of post transplant lymphoproliferative disorder (n=1). All but one (90.9%) of the for-cause AUC analyses merited dose adjustments. Three patients had baseline nausea; one displayed a supratherapeutic AUC. One reported nausea abatement following MMF decrease whereas two spontaneously resolved. Five reports of leukopenia were found, three with AUCs above 60 mg*h/L. All leukocyte levels normalized following MMF dosage reduction. Conclusion Patient specific tailoring of MMF via therapeutic drug monitoring of MPA AUC in pOHT may increase tolerability and diminish short and long term side effects of therapy.