Free Fraction Of Mycophenolic Acid Research Articles

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

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

Pharmacokinetics and pharmacodynamics of mycophenolic acid in Nagase analbuminemic rats: Evaluation of protein binding effects using the modeling and simulation approach

This study aimed to examine the pharmacokinetics and pharmacodynamics of mycophenolic acid (MPA) in Nagase analbuminemic rats (NARs) to evaluate the effect of protein binding on the associated inosine-5ʹ-monophosphate dehydrogenase (IMPDH) activity. Free fractions of MPA in the control rats and NARs were 2.09 and 24.8%, respectively. Pharmacokinetic and pharmacodynamic parameters simultaneously obtained by the nonlinear mixed effects modeling program NONMEM explained reasonably well the concentrations of MPA and MPA glucuronide as well as IMPDH activity in both rats. NARs showed a higher clearance and a smaller volume of distribution based on the free MPA concentration than the controls did, besides the increase in free fraction. The half-maximal inhibitory concentration based on free MPA was estimated as 163 ng/mL for both rats. Simulations based on the obtained pharmacokinetic and pharmacodynamic parameters showed that the area under the IMPDH activity-time curve decreased non-linearly according to the increase in free fraction of MPA. In conclusion, the experimental data obtained from NARs followed by the modeling and simulation approach quantitatively clarified that the free MPA concentration was suitable for the biomarker of immunosuppressive effect of MPA. Dose adjustments based on the total MPA may cause unnecessary overexposure to MPA in patients with hypoalbuminemia.

Mycophenolate pharmacokinetics and inosine monophosphate dehydrogenase activity in liver transplant recipients with an emphasis on therapeutic drug monitoring

Background. The pharmacokinetics of the immunosuppressant mycophenolic acid (MPA) demonstrates high inter- and intra-patient variability. Variation in the binding of MPA to albumin has been postulated to be an important factor in this variability, and monitoring of free MPA has been suggested to improve therapeutic drug monitoring (TDM) of MPA. Inosine monophosphate dehydrogenase (IMPDH) is the target enzyme for MPA, therefore the IMPDH activity in lymphocytes can serve as a marker of the MPA-specific response. This study aimed to explore how the albumin concentration influences the free concentration of MPA in liver transplant recipients and to assess whether alteration in the free MPA influences IMPDH activity in CD4 + cells. Methods. Blood samples were taken from 20 liver transplant recipients on two separate occasions (days 3–5 and 16–21). Total and free concentrations of MPA, and IMPDH activity were measured during the first 4 h of each dose interval. Results. Albumin levels correlated with the free fraction of MPA. However, the total MPA and free MPA were equal predictors of the immunosuppressive response as defined by IMPDH activity. Conclusion. Total and free MPA are equally good predictors of the immunosuppressive effect exerted by MPA as defined by IMPDH activity. IMPDH activity measurements represent a promising approach to TDM in patients treated with MPA.

Pharmacokinetics of tacrolimus and mycophenolate mofetil in renal transplant recipients on a corticosteroid-free regimen

The pharmacokinetics of both tacrolimus and mycophenolic acid in renal transplant recipients on a corticosteroid-free regimen was evaluated. Upon administration of steady-state morning tacrolimus and mycophenolate mofetil doses, 28 patients for whom at least three months had passed after renal transplantation underwent serial blood sample collection over a 12-hour dosing period. Whole blood concentrations of tacrolimus were measured, as were mycophenolic acid, mycophenolic acid 7-0-glucuronide (MPAG), and acyl glucuronide MPAG (AcMPAG) concentrations. Pharmacokinetic parameters were then analyzed by conventional noncompartmental modeling. The mean ± S.D. pharmacokinetic parameters for tacrolimus, normalized to a dose of 1 mg, were as follows: area under the concentration-time curve (AUC), 52.6 ± 24.8 μg · hr/L/mg; maximum concentration (C(max)), 8.0 ± 3.3 μg/L/mg; time to C(max) (t(max)), 1.8 ± 1.0 hr; and minimum concentration (C(min)), 2.6 ± 1.4 μg/L/mg. The mean ± S.D. pharmacokinetic parameters for mycophenolic acid, normalized to a mycophenolate mofetil dose of 1 g, were AUC, 26.9 ± 13.2 μg ·hr/mL/g; C(max), 17.5 ± 5.4 μg/mL/g; t(max), 0.9 ± 0.6 hr; and C(min), 1.5 ± 1.1 μg/mL/g. The free fraction of mycophenolic acid was 1.8% ± 0.7%. AUC ratios of MPAG:mycophenolic acid and AcMPAG:mycophenolic acid were 13.0 ± 5.8 and 0.1 ± 0.2, respectively. Overall exposure and C(min) values for tacrolimus were similar but C(max) values were higher than those documented in renal transplant patients treated with corticosteroid-based regimens. This may have clinical implications in corticosteroid-free patients experiencing symptoms of tacrolimus toxicity despite trough levels within target ranges. Mycophenolic acid exposure increased with time, but AUC values fell within the range expected for patients receiving concurrent corticosteroids.

Pharmacokinetic Variability of Mycophenolic Acid and Its Glucuronide in Systemic Lupus Erythematosus Patients in Remission Maintenance Phase

The aim of this study was to identify factors affecting the pharmacokinetics of mycophenolic acid (MPA) and its 7-O-glucuronide (MPAG) in systemic lupus erythematosus (SLE) patients. Thirty-one SLE patients in remission maintenance phase treated with mycophenolate mofetil (median 1500 mg/d) and prednisolone and followed-up for up to 56 months (median 13 months) were enrolled. Creatinine clearance and metal medication were significant predictors accounting for interindividual variability in the dose-normalized predose plasma concentration (C₀) of MPA (adjusted R²=0.305, p=0.01) in a multivariate analysis. Dose-normalized MPAG C₀ was significantly correlated with only creatinine clearance (adjusted R²=0.135, p=0.03). The free fraction of MPA was significantly correlated with only serum albumin (adjusted R²=0.700, p<0.01). The free fraction of MPAG was significantly correlated with serum albumin, metal medication, and age (adjusted R²=0.598, p=0.02). In conclusion, renal function and co-administered metal influenced the pharmacokinetics of MPA and MPAG in SLE patients in remission maintenance phase.

High-Performance Liquid Chromatography-Mass Spectroscopy/Mass Spectroscopy Method for Simultaneous Quantification of Total or Free Fraction of Mycophenolic Acid and its Glucuronide Metabolites

Measurement of unbound fractions of mycophenolic acid and its metabolites may prove useful in explaining the complicated pharmacokinetic and pharmacodynamic behavior of this drug as well as in therapeutic drug monitoring. We developed a reliable, accurate, and sensitive liquid chromatography-tandem mass spectrometric method for the simultaneous quantification of mycophenolic acid (MPA), MPA glucuronide (MPAG), and MPA acyl-glucuronide (AcMPAG), total or unbound, in plasma, urine, and tissue extract. This method uses a single internal standard, carboxy-butoxy ether of mycophenolic acid (MPAC), and involves a simple sample preparation step. Aliquots of plasma, urine, or dissolved tissue extract (100 microL) or plasma ultrafiltrate for free analytes (50 microL) are treated with acetonitrile/formic acid mixture (99.5/0.5 v/v) followed by centrifugation and dilution with water. The prepared samples are then injected onto an extraction column (Eclipse XDB-C18 12.5 x 4.1 mm; Agilent Technologies, Palo Alto, CA) and washed with mobile phase composed of acetonitrile/water/formic acid (10/89.5/0.5 v/v/v) at a flow rate of 2.8 mL/min. A switching valve is activated 1 minute after sample injection. The analytes are eluted onto the analytical column (Eclipse XDB-C18 150 x 4.1 mm; Agilent Technologies) with a gradient of 0.5% aqueous formic acid, methanol, acetonitrile, and water. We used a tandem mass spectrometer with electrospray ion source, in which the tandem mass spectroscopy transitions were (m/z): 338-->207 for MPA, 438-->303 for MPAC, and 514-->303 for MPAG and AcMPAG. The dynamic ranges (lower limit of quantitation and upper limit of quantitation) were as follows: 0.05 to 30 mg/L for total MPA and 1 to 300 microg/L for free MPA; 0.5 to 300 mg/L of total MPAG and 0.2 to 60 mg/L for free MPAG; and 0.025 to 15 mg/L of total AcMPAG and 1 to 60 microg/L for free AcMPAG. The precision at lower limit of quantitation was in the range of 8.0% to 11.9% for all three total analytes and 13.8 to 18.7% for the free analytes. Accuracy at lower limit of quantitation was in the range of 100% to 105% for total and 97% to 99% for free analytes. Between-day precision of quality control samples was 4.0% to 6.3% for human plasma spiked with total analytes and 4.5% to 14.4% for spiked plasma ultrafiltrate for free analytes. Mean absolute recovery ranged from 98.5% to 101.7% for MPA (both total and free), from 78.1% to 103.4% for MPAG and from 91.5% to 110.4% for AcMPAG. No significant ion suppression was found under these conditions for any of the analytes. Carryover effect was found to be at a maximum level of 0.02%. This method was successfully applied to analyze over 11,000 samples for total analytes, and over 8000 samples for free analytes in plasma, and has been in operation for nearly 3 years without loss of performance.

Evaluation of MPA and MPAG Removal by Continuous Venovenous Hemodiafiltration and Continuous Venovenous Hemofiltration

The study assessed the removal of mycophenolic acid (MPA) and its major glucuronide metabolite (MPAG) during continuous venovenous hemofiltration (CVVHF) and continuous venovenous hemodiafiltration (CVVHDF) in 4 heart transplant recipients treated for at least 6 days with mycophenolate mofetil (MMF) in addition to cyclosporine and corticosteroids. The sieving coefficient ranged from 0.02 to 0.04 for MPA and from 0.15 to 0.33 for MPAG. The clearance of MPAG by CVVHDF or CVVHF ranged from 7.52 mL/min to 19.45 mL/min, and that of MPA was lower than 2.28 mL/min, with no significant difference between the two continuous replacement therapies. Whereas MPA percentage recovered by hour following CVVHDF or CVVHF was negligible, the percentage of MPAG represents up to 12.9% of the administered dose. A relevant decrease in the free fraction of MPA and MPAG was observed after continuous renal replacement therapy (CRRT). These preliminary results demonstrate that MPAG is able to permeate the filter. In light of the alteration in protein binding following CRRT and the competition between MPA and MPAG to albumin site, drug monitoring of MPA and MPAG in patients undergoing CVVHDF or CVVHF may be suggested. Moreover, monitoring of free MPA may be of interest for these patients.

Immunosuppression in Pediatric Liver and Intestinal Transplantation: A Closer Look at the Arsenal

Immunosuppression in Pediatric Liver and Intestinal Transplantation: A Closer Look at the Arsenal

Mycophenolic acid pharmacokinetics and related outcomes early after renal transplant

The pharmacokinetics of mycophenolic acid and its glucuronide are complex. This study investigated the pharmacokinetics, pharmacodynamics and protein binding of mycophenolic acid and its glucuronide metabolite, early post-transplant in renal allograft recipients. Forty-two de novo renal transplant recipients receiving mycophenolate mofetil and concomitant cyclosporin (n = 32) or tacrolimus (n = 10) participated in the study. Blood samples were taken on day 5 post-transplant for measurement of free and total concentrations of mycophenolic acid, mycophenolic acid glucuronide and relevant biochemistry. Associations between free fraction and biochemistry were investigated. Free and total 6-h area under the concentration-time curve (AUC0-6) of mycophenolic acid was assessed relative to clinical outcomes in the first month post-transplant. Kinetic variability of free and total mycophenolic acid and its glucuronide was greater in patients on cyclosporin (12- to 18-fold variation) than on tacrolimus (four- to fivefold) cotherapy. Cyclosporin-treated patients also had significantly lower predose total mycophenolic acid concentrations than tacrolimus-treated patients (median 0.8 mg l(-1) and 1.6 mg l(-1), respectively, P = 0.002). Mycophenolic acid glucuronide predose concentration correlated positively with mycophenolic acid glucuronide AUC0-6 (r > 0.95). Mycophenolic acid free fraction varied 11-fold, from 1.6% to 18.3%, whilst the glucuronide free fraction varied threefold, from 17.4% to 54.1%. Urea and creatinine concentrations correlated positively (r > 0.46), whilst albumin correlated negatively (r = -0.54) with free fraction of mycophenolic acid. Similar relationships were found for the free fraction of mycophenolic acid glucuronide. Mycophenolic acid free fraction was on average 70% higher in patients with albumin concentrations below a specified albumin cut-off concentration of 31 g l(-1)[free fraction = 7 +/- 4% for lower albumin and 4 +/- 3% for higher albumin, respectively; P = 0.001; 95% confidence interval (CI) for the difference 1.9, 4.2]. Neither free nor total mycophenolic acid AUC0-6 was related to rejection (P > 0.07). Free AUC0-6 was significantly higher in those patients with thrombocytopenic, leukopenic and/or infectious outcomes than in those without (mean +/- SD 1.9 +/- 0.3 mg h(-1) l(-1) and 1.1 +/- 0.1 mg h(-1) l(-1), P = 0.0043; 95% CI for the difference 0.3, 1.4). The marked variability in mycophenolic acid/glucuronide pharmacokinetics occurring early post-transplant during the current study was greater in cyclosporin (12-18-fold) than in tacrolimus (four- to fivefold) treated patients. Concomitant cyclosporin was associated with total mycophenolic acid concentrations approximately half that of tacrolimus. Patients with marked renal impairment had the highest free fractions reported to date. The exposure to unbound mycophenolic acid was significantly related to infections and haematological toxicity.

Pharmacokinetics of mycophenolic acid (MPA) and determinants of MPA free fraction in pediatric and adult renal transplant recipients. German Study group on Mycophenolate Mofetil Therapy in Pediatric Renal Transplant Recipients.

Dosage guidelines for mycophenolate mofetil (MMF), an ester prodrug of the immunosuppressant mycophenolic acid (MPA), are still preliminary in children. This study compares the pharmacokinetics of MPA and its major metabolite MPA glucuronide (MPAG) in pediatric renal transplant recipients receiving 600 mg MMF/m2 body surface area twice a day to those of adults on the currently recommended oral dose of 1 g of MMF twice a day. Concentration-time profiles of 18 children (age, 10.7+/-0.72 yr; range, 5.9 to 15.3 yr) and 10 adults were investigated 1 and 3 wk after transplantation. Plasma concentrations of MPA and MPAG were measured by reverse-phase HPLC. Because MPA is extensively bound to serum albumin and only the free fraction is presumed to be pharmacologically active, the MPA free fraction was also analyzed by HPLC after separation through ultrafiltration. The areas under the concentration-time curves (AUC0-12) of total and free MPA throughout the 12-h dosing interval in children were, in general, comparable to the corresponding data in adult patients. The mean AUC0-12 of MPA and free MPA did not change significantly over the first 3 wk after transplantation, but there was substantial intra- and interindividual variation. MPAG-AUC0-12 values in children with primary renal transplant dysfunction were threefold higher than in those with functioning transplants. Renal impairment had no consistent effect on total MPA-AUC0-12 values, but the MPA free fraction in children (median, 1.65%; range, 0.40 to 13.8%) was significantly (r2=0.46) modulated by renal transplant function and serum albumin levels. In conclusion, concentration-time profiles of pediatric renal transplant recipients administered 600 mg MMF/m2 body surface area twice a day are comparable to those in adults on 1 g MMF twice a day in the first 3 wk after transplantation. Renal impairment and decreased serum albumin levels led to an increase in the free fraction of MPA and the free MPA-AUC0-12 values. Because the pharmacologic activity of MPA is a function of unbound drug concentration, these findings might be relevant for the pharmacodynamic effects of MPA.