Therapeutic drug monitoring of mycophenolate mofetil in transplantation

Comparison of high-performance liquid chromatography and enzyme-multiplied immunoassay technique to monitor mycophenolic acid in paediatric renal recipients

Therapeutic drug monitoring (TDM) of mycophenolate mofetil (MMF) is recommended to guide immunosuppression. High-performance liquid chromatography with ultraviolet (HPLC-UV) or the enzyme-multiplied immunoassay technique (EMIT), used to measure mycophenolic acid (MPA) were compared in an exclusive paediatric renal transplant population. Twenty patients were included as part of the pharmacokinetics study of MMF, and 88 additional samples were drawn for TDM. Agreement between HPLC-UV and EMIT was assessed by the Bland-Altman method. With the two methods, pre-dose concentrations were not normally distributed. After logarithmic transformation, their mean was 0.79 +/- 1.16 microg ml(-1) and their mean difference was 0.34 +/- 0.16 microg ml(-1) [95% confidence interval (95%CI 0.30-0.38 microg ml(-1), with antilogarithmic values of these limits of 1.34-1.46 microg ml(-1)). Area under the curve (AUC)(HPLC) and AUC(EMIT) were normally distributed. Their mean was 52.42 +/- 25.91 mg x h/l and their mean difference was 15.22 +/- 8 mg x h/l (95%CI 11.99-18.45 mg x h/l), the Bland-Altman plot showing a bias proportional to the mean. Our data showed the absence of agreement between the HPLC and EMIT methods, with an average positive bias of 15% with the EMIT. Further studies are required to determine which method is best appropriate for TDM of MMF in children.

Pharmacokinetic study of mycophenolate mofetil in patients with systemic lupus erythematosus and design of Bayesian estimator using limited sampling strategies

BACKGROUND

Monitoring of the area under the plasma concentration-time curve (AUC) of mycophenolic acid (MPA) has been developed for individual dose adjustment of mycophenolate mofetil (MMF) in renal allograft recipients. MMF is currently used as an off-label drug in the treatment of systemic lupus erythematosus (SLE), but factors of its exposition may be different in these patients and need to be determined for therapeutic drug monitoring (TDM) purposes.

OBJECTIVE

The aim of the study was to develop a maximum a posteriori probability (MAP) Bayesian estimator of MPA exposition in patients with SLE, with the objective of TDM based on a limited sample strategy.

METHODS

Twenty adult patients with SLE given a stable 1 g/day, 2 g/day or 3 g/day dose of MMF orally for at least 10 weeks were included in the study. MPA was measured by high-performance liquid chromatography (HPLC) coupled to a photodiode array detector (11 plasma measurements over 12 hours post-dose per patient). Free MPA concentrations were measured by HPLC with fluorescence detection. Two different one-compartment models with first-order elimination were tested to fit the data: one convoluted with a double gamma distribution to describe secondary concentrations peaks, and one convoluted with a triple gamma distribution to model a third, later peak.

RESULTS

A large interindividual variability in MPA concentration-time profiles was observed. The mean maximum plasma concentration, trough plasma concentration, time to reach the maximum plasma concentration and AUC from 0 to 12 hours (AUC(12)) were 13.6 +/- 8.4 microg/mL, 1.4 +/- 1.2 microg/mL, 1.1 +/- 1.2 hours and 32.2 +/- 17.1microg . h/mL, respectively. The mean free fraction of MPA was 1.7%. The one-compartment model with first-order elimination convoluted with a triple gamma distribution best fitted the data. Accurate Bayesian estimates of the AUC(12) were obtained using three blood samples collected at 40 minutes, 2 hours and 3 hours, with a coefficient of correlation (R) = 0.95 between the observed and predicted AUC(12) and with a difference of <20% in 16 of the 20 patients.

CONCLUSION

A specific pharmacokinetic model was built to accurately fit MPA blood concentration-time profiles after MMF oral dosing in SLE patients, which allowed development of an accurate Bayesian estimator of MPA exposure that should allow MMF monitoring based on the AUC(12) in these patients. The predictive value of targeting one specific or different AUC values on patients' outcome using this estimator in SLE will need to be evaluated.

Combination of CsA, MTX and low-dose, short-course mycophenolate mofetil for GVHD prophylaxis

In an effort to reduce the incidence and severity of acute GVHD (aGVHD), we have developed a new prophylaxis regimen combining cyclosporine and MTX with a short 30-day course of low-dose (500 mg per day) mycophenolate mofetil. This regimen was studied prospectively 100 patients undergoing HLA-matched and 1-antigen-mismatched allogeneic peripheral blood SCT from related donors. The cumulative incidence of aGVHD was 16% (grades II-IV (9.5%) and grades III-IV (1%)). The cumulative incidence of chronic GVHD (cGVHD) was 53% with 28% extensive cGVHD. The cumulative incidence of transplant-related mortality at 100 days and 3 years were 6 and 13%. The estimated probabilities of disease-free survival at 3 years in standard- and high-risk patients were 77 and 30%, respectively (P<0.0001). The estimated probabilities of overall survival at 3 years in standard- and high-risk patients were 77 and 37%, respectively (P<0.0001). These data show a substantial decrease in the risk of developing aGVHD without an increase in relapse or any adverse impact on survival in standard-risk patients.

Preliminary experience with renal transplantation in HIV+ recipients: low acute rejection and infection rates

BACKGROUND

Only four centers have reported their results with renal transplantation in human immunodeficiency virus (HIV)+ recipients on highly active antiretroviral therapy, and acute rejection (AR) rates have consistently ranged from 43% to 67%.

METHODS

We examined the outcomes of eight adult HIV+ primary renal allograft recipients with median 15 (range 8-47) months follow-up with multiple other high-risk factors, including African American ethnicity, hepatitis C virus (HCV) positivity, long waiting times, prior sensitization, paucity of live donors, and delayed graft function. Our immunosuppressive protocol consisted of an anti-interleukin-2 receptor antibody for induction, and mycophenolate mofetil, cyclosporin A, and prednisone for maintenance. Initial and 3- to 6-month cyclosporin A trough level targets were 250 to 300 and 225 to 275 ng/mL, respectively, and mycophenolate mofetil dose was adjusted according to 2 to 4 week surveillance and subsequent as needed mycophenolic acid predose concentrations during the first 6 months.

RESULTS

Patient and graft survival were 100% and 88%, respectively, with an AR rate of 13% and excellent renal function. No patients developed new-onset diabetes, opportunistic or other serious infections, malignancy, or progression of hepatitis C virus-related liver disease. Excellent suppression of HIV replication with maintenance of CD4 counts was noted in all cases.

CONCLUSIONS

Our findings suggest that HIV+ patients on highly active antiretroviral therapy can undergo successful renal transplantation with a low incidence of both AR and AIDS-associated and non-AIDS associated infections, despite associated risk factors for poorer outcome. Our encouraging but preliminary results with this protocol will need to be verified in larger numbers of HIV+ renal allograft recipients with longer follow-up.

First clinical experience with the new once-daily formulation of tacrolimus

Once-daily tacrolimus is a new oral formulation of the established immunosuppressive agent tacrolimus (Prograf, Astellas Pharma US, Inc., Deerfield, IL), which is administered twice daily. It has been approved in the European Union for prophylaxis of rejection in liver and kidney transplant recipients, where it is registered as Advagraf, and in Canada for the prophylaxis of rejection in kidney transplant recipients, and is currently under review in the United States and Japan. Studies with once-daily tacrolimus have been performed in de novo kidney and liver transplant recipients, and conversion studies have been performed in stable adult kidney and liver transplant recipients and stable pediatric liver transplant recipients, who were converted on an mg:mg basis from twice-daily tacrolimus to a single morning dose of the new formulation. Results of these studies have established the safety and efficacy of this once-daily dosing alternative. Therapeutic regimens for transplant recipients are often complex, contributing to a high incidence of medication noncompliance and its consequences of increased mortality and morbidity. The tacrolimus once-daily regimen may improve compliance while enabling the use of the same patient care strategies, total daily dose, target trough concentrations, and therapeutic monitoring techniques as currently used with the twice-a-day formulation of tacrolimus.

Association between mycophenolic acid 12-h trough levels and clinical endpoints in patients with autoimmune disease on mycophenolate mofetil

BACKGROUND

Triggered by heightened interest in mycophenolate mofetil (MMF) for the treatment of autoimmune diseases (AID) and encouraged by the results from a previous study, we hypothesized that therapeutic drug monitoring of mycophenolic acid (MPA) based on troughs may be useful for effective MMF dosing in patients with AID.

METHODS

A two-step approach was pursued. First, we confirmed in 38 AID patients (26 with antineutrophil cytoplasmic antibody-associated vasculitis; 12 with systemic lupus erythematosus) a significant correlation (r = 0.545, P < 0.001) between MPA C(12 h) and MPA exposure (AUC). Second, we performed an analysis of 294 MPA 12-h trough levels serially collected from 39 patients (same indications) receiving MMF for remission maintenance therapy to elucidate possible associations with disease activity and MMF toxicity.

RESULTS

Higher MPA trough levels were associated with better protection from recurrence of active disease. While at levels <3 mg/L 29% of collected samples (43/147) were from patients with active disease, this was only the case in 2% of samples (3/147) with an MPA concentration of >or=3 mg/L. Remission persisted in all patients with MPA troughs >or=3.5 mg/L. Upon combined analysis of efficacy and safety data, most favourable results were obtained with MPA troughs between 3.5 and 4.5 mg/L. There was no discernable relationship between MMF dose and clinical endpoints.

CONCLUSION

The target range proposed by this explorative study may serve as an initial guidance for MPA monitoring in the context of further prospective controlled trials in patients with AID.

Pharmacogenetic effect of the UGT polymorphisms on mycophenolate is modified by calcineurin inhibitors

BACKGROUND

Mycophenolic acid (MPA) is glucuronidated primarily by uridine diphosphate glucuronosyltransferase enzymes (UGT) 1A9 and 1A8. These enzymes are highly polymorphic resulting in low activity and high expression phenotypes. We hypothesized that polymorphisms of UGT1A9 and 1A8 may alter MPA pharmacokinetics in kidney transplantation.

METHODS

One hundred seventeen kidney (n = 93), pancreas (n = 11), or simultaneous kidney and pancreas (SPK) (n = 13) transplant recipients were studied for the effect of UGT1A9 and UGT1A8 polymorphisms on MPA dose-corrected trough concentrations. Individuals were genotyped for UGT1A8 and UGT1A9 polymorphisms (1A8*2, 1A8*3, 1A9*3, 1A9-275 and 1A9-2152). Linear regression was used to estimate the effect of UGT polymorphisms on the individual's mean MPA dose-corrected trough concentration with and without stratification by calcineurin inhibitor. A multiple linear regression analysis was performed to assess the dependence between the average MPA dose-corrected trough concentration and age, gender, UGT genotype (1A8*2, 1A8*3, 1A9*3, 1A9-275, 1A9-2152), serum albumin, hemoglobin (Hgb), hematocrit (HCT), liver transaminases (AST, ALT), serum creatinine, and bilirubin.

RESULTS

Mycophenolic acid dose-corrected trough concentrations were 60% higher in subjects heterozygous or homozygous for UGT1A8*2 than in those with the wild type (p = 0.02); however, this effect was dependent on concomitant calcineurin inhibitor. When subjects were stratified by calcineurin inhibitor status, the UGT1A8*2 effect was only apparent in the tacrolimus group (p < 0.01). Mycophenolic acid dose-corrected trough concentrations were 70% lower in carriers of the UGT1A9 -275T>A/-2152 C>T polymorphism who received cyclosporine (p < 0.01). There was no effect of the UGT1A9 -275T>A/-2152C>T polymorphism in the tacrolimus group.

CONCLUSIONS

The effect of UGT1A8 and UGT1A9 variants on MPA metabolism appears to be modified by concomitant calcineurin inhibitor therapy. Confirmatory in vivo and in vitro studies are needed.

C-440T/T-331C polymorphisms in the UGT1A9 gene affect the pharmacokinetics of mycophenolic acid in kidney transplantation

INTRODUCTION

The immunosuppressive agent mycophenolic acid (MPA) is metabolized by uridine diphosphate glucuronosyltransferase 1A9 (UGT1A9) to 7-O-glucuronide (MPAG) and excreted by multidrug resistance-associated protein 2 in the bile. By contrast, the production of the acyl MPAG, a minor MPA metabolite, was ascribed to UGT2B7 and UGT1A8. Several polymorphisms in the genes encoding for UGT1A9, UGT2B7 and MRP2 proteins have been described. However, their functional role in vivo on MPA metabolism remains poorly defined.

METHODS

A total of 40 Caucasian kidney transplant patients, given induction therapies (with Campath-(1)H or the combination basiliximab/rabbit antithymocyte globulin) and on maintenance immunosuppression with cyclosporine in combination with mycophenolate mofetil (MMF) in a steroid-free regimen, were enrolled in the pharmacogenetic study. Patients had clinical and hematochemical evaluations at month 6 after transplantation, as well as complete MPA pharmacokinetic assessment. They were genotyped for SNPs in UGT1A9 C-2152T, T-1887G, C-665T, C-440T, T-331C, T-275A, T98C, for the nonsynonymous C802T SNP in UGT2B7, and for ABCC2 SNPs C-24T and G1249A. The association of these polymorphisms with MPA pharmacokinetic parameters was investigated.

RESULTS

Differences in the MPA pharmacokinetic profiles confirmed large interpatient variability of MPA exposure, with AUC(0-12) values ranging from 7.9 to 50.1 mg*h/ml. MPA AUC(0-12) was significantly associated with the presence of UGT1A9 -440/-331 genotypes (TT/CC: 61.5 +/- 2.7 mg*h/ml/g MMF; TC/CT: 45.4 +/- 14.0 mg*h/ml/g MMF; CC/TT: 40.8 +/- 10.8 mg*h/ml/g MMF; p = 0.005), whereas MPAG exposure was mainly influenced by renal function. The positive association between MPA AUC and SNPs in position -440/-331 found in kidney transplant patients confirmed previous in vitro findings showing that the abovementioned SNPs had a significant impact on UGT1A9 protein content in the liver. The presence of ABCC2 promoter C-24T and exon 10 G1249A SNPs did not cause any significant variation in MPA and MPAG pharmacokinetic parameters.

CONCLUSION

The study demonstrated a significant impact of C-440T/T-331C SNPs in the promoter region of the UGT1A9 gene on MPA pharmacokinetics in renal allograft recipients.

Performance of limited sampling strategies for predicting mycophenolic acid area under the curve in thoracic transplant recipients

BACKGROUND AND METHODS

Eight limited sampling strategies (LSSs) for estimating mycophenolic acid area under the concentration-time curve (4 developed from lung transplant recipients at our center, 4 developed for heart transplant recipients from other research groups) were evaluated in 27 heart or heart-kidney transplant patients.

RESULTS

The LSSs from our lung transplant patients performed well when applied to the heart transplant population, with percent bias and percent precision within the acceptable limit of +/-15%.

CONCLUSIONS

The LSSs developed at our center are robust enough to be applied to both lung and heart transplant populations. Application of LSSs from other research groups yielded less optimal results, reinforcing the need to re-establish or re-validate LSSs for each specific center.

A review of albumin binding in CKD

Hypoalbuminemia is associated with excess mortality in patients with kidney disease. Albumin is an important oxidant scavenger and an abundant carrier protein for numerous endogenous and exogenous compounds. Several specific binding sites for anionic, neutral, and cationic ligands were described. Overall, the extent of binding depends on the ligand and albumin concentration, albumin-binding affinity, and presence of competing ligands. Chronic kidney disease affects all these determinants. This may result in altered pharmacokinetics and increased risk of toxicity. Renal clearance of albumin-bound solutes mainly depends on tubular clearance. Dialytic clearance by means of conventional hemodialysis/hemofiltration and peritoneal dialysis is limited. Other epuration techniques combining hemodialysis with adsorption have been developed. However, the benefit of these techniques remains to be proved.

Targeting mycophenolate mofetil for graft-versus-host disease prophylaxis after allogeneic blood stem cell transplantation

As low trough levels of mycophenolic acid (MPA) have been measured in recipients of allo-SCTs, we performed a pilot study targeting mycophenolate mofetil (MMF) doses according to the MPA area under the concentration (AUC) levels. Twenty-nine patients were transplanted from matched sibling (n=7) and unrelated donors (n=22). Tacrolimus was given orally from day -1 to achieve trough blood levels of 5-10 ng/ml. MMF was started on day 0 at 1500 mg intravenously b.i.d. AUC measurements of MPA by HPLC were scheduled on days 3, 7 and 11 after transplantation. The MMF dose was modified to achieve an MPA AUC of 35-60 microg/ml/h. With the respective adjustments 66 and 75% surpassed the lower AUC target on days 7 and 11, respectively. The cumulative incidence of grade III-IV acute GVHD was 28% (8/29). Eight out of 24 evaluable patients (33%) suffer from limited (n=3) or extensive (n=5) chronic GVHD. Overall, the results of this study suggest that targeting of MPA exposure is feasible early after transplantation. A simplified MMF targeting strategy based on MPA C(max) or C(2h) levels seems to be warranted in future trials involving more patients at later time points in the outpatient setting.

Calcineurin-inhibitor avoidance in elderly renal allograft recipients using ATG and basiliximab combined with mycophenolate mofetil

In old recipients of renal allografts from old donors, benefits of calcineurin-inhibitors (CNI) are curtailed by nephrotoxicity. Intending to improve the outcome of these recipients, we analyzed a CNI-free immunosuppressive regimen consisting of anti-thymocyte globulin (ATG), basiliximab, mycophenolate mofetil (MMF) and steroids. Kidney allograft recipients with low immunological risk (panel reactive antibodies <30%) were eligible for this study. Immunosuppression induction included ATG (4 mg/kg, day 0), basiliximab (20 mg, day 0 + 4) and steroids, followed by MMF (TL 2-6 microg/ml) and steroid maintenance treatment. Patient and graft survival rates respectively were 89.3% and 85.4% (12 months), and 86.6% and 76.8% (24 months). Delayed graft function occurred in 44.6%. S-creatinine at 12 months was 1.85 +/- 0.94 mg/dl. Thirty patients (53.6%) showed biopsy-proven rejections (6x Banff 3, 13x Banff 4I and 16x Banff 4II), 77% of which were steroid-sensitive, 23% required antibody treatment. After 12 months, 83% of the patients had an MMF-based immunosuppression, 43% were CNI-free. Cytomegalovirus (CMV) infections occurred in 28, tissue-invasive disease in three patients. Despite acceptable renal graft survival and function in some of patients with marginal organs, high incidences of rejections and CMV infections suggest the feasibility of CNI-avoidance using an MMF-based protocol only in carefully selected patients.

Population pharmacokinetic modelling for enterohepatic circulation of mycophenolic acid in healthy Chinese and the influence of polymorphisms in UGT1A9

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

Mycophenolic acid (MPA) undergoes enterohepatic circulation (EHC) in the body and several population models have been proposed to describe this process using sparse data. Recent studies in Whites have found that polymorphism in UGT1A9 could partly explain the large interindividual variability associated with the pharmacokinetics of MPA.

WHAT THIS STUDY ADDS

A new population pharmacokinetic model for EHC combining MPA and its main glucuronide metabolite (MPAG) simultaneously was established based on physiological aspects of biliary excretion using intensive sampling data. Pharmacokinetic profiles of MPA and MPAG with the UGT1A9 polymorphism in healthy Chinese were characterized. AIMS To establish a population pharmacokinetic model that describes enterohepatic circulation (EHC) of mycophenolic acid (MPA) based on physiological considerations and to investigate the influence of polymorphisms of UGT1A9 on the pharmacokinetics of MPA.

METHODS

Pharmacokinetic data were obtained from two comparative bioavailability studies of oral mycophenolic mofetil formulations. Nonlinear mixed effects modelling was employed to develop an EHC model including both MPA and its main glucuronide metabolite (MPAG) simultaneously. Demographic characteristics and UGT1A9 polymorphisms were screened as covariates.

RESULTS

In total, 590 MPA and 589 MPAG concentration-time points from 42 healthy male volunteers were employed in this study. The chain compartment model included an intestinal compartment, a gallbladder compartment, a central and a peripheral compartment for MPA and a central compartment for MPAG. The typical population clearance (CL/F) estimates with its relative standard error for MPA and MPAG were 10.2 l h(-1) (5.7%) and 1.38 l h(-1) (6.9%), respectively. The amount of MPA recycled in the body was estimated to be 29.1% of the total amount absorbed. Covariate analysis showed that body weight was positively correlated with CL/F of MPA, intercompartment CL/F of MPA and distribution volume of MPA peripheral compartment. Polymorphisms of UGT1A9 did not show any effect on the pharmacokinetics of MPA and MPAG. The model evaluation tests indicated that the proposed model can describe the pharmacokinetic profiles of MPA and MPAG in healthy Chinese subjects.

CONCLUSIONS

The proposed model may provide a valuable approach for planning future pharmacokinetic-pharmacodynamic studies and for designing proper dosage regimens of MPA.

Evaluation of the practicability of limited sampling strategies for the estimation of mycophenolic acid exposure in Chinese adult renal recipients

The immunosuppressive potential of mycophenolic acid (MPA) correlates well with MPA exposure [area under the concentration-time curve (AUC)]. Monitoring MPA AUC is important and helpful for maintaining the efficacy of mycophenolate mofetil while minimizing its side effects, but full MPA AUC monitoring is laborious, cost prohibitive, and impractical. Limited sampling strategies have been proposed as an alternative method for estimating MPA exposure. The objective of this study was to evaluate the practicability of different limited sampling strategies for the estimation of MPA exposure. A total of 56 pharmacokinetic profiles from 53 adult renal recipients were used to evaluate the practicability of 10 published models. Standard correlation and linear regression analysis were used to compare the estimated MPA AUCs and corresponding full MPA AUCs, and the percentage of profiles for which prediction error fell within +/-20% was also used to assess the practicability of these models. Agreement between the estimated MPA AUCs and full MPA AUCs was further tested by Bland and Altman analysis. The model, based on four sampling time points, used the formula AUC = 12.61 + 0.37 x C0.5 + 0.49 x C1 + 3.22 x C4 + 8.17 x C10, was superior to all other evaluated models, with the highest coefficient of determination (r = 0.88), a low percentage prediction error (2.79%), and good agreement according to Bland and Altman analysis. Prediction errors of 87.5% (49/56) of profiles were within 20%, which was the highest of all the models. This algorithm can be reliably used for estimating MPA exposure in adult renal transplant patients treated with cyclosporine as concomitant immunosuppressant. Another model based on the formula AUC = 8.22 + 3.16 x C0 + 0.99 x C1 + 1.33 x C2 + 4.18 x C4 also has acceptable predictive performance, and it may also be practical, especially in outpatient settings, in view of its distribution of time points.

Validation of limited sampling strategy for the estimation of mycophenolic acid exposure in Chinese adult liver transplant recipients

Mycophenolate mofetil (MMF) is indicated as immunosuppressive therapy in liver transplantation. The abbreviated models for the estimation of mycophenolic acid (MPA) area under the concentration-time curve (AUC) have been established by limited sampling strategies (LSSs) in adult liver transplant recipients. In the current study, the performance of the abbreviated models to predict MPA exposure was validated in an independent group of patients. A total of 30 MPA pharmacokinetic profiles from 30 liver transplant recipients receiving MMF in combination with tacrolimus were used to compare 8 models' performance with a full 10 time-point MPA-AUC. Linear regression analysis and Bland-Altman analysis were used to compare the estimated MPA-AUC0-12h from each model against the measured MPA-AUC0-12h. A wide range of agreement was shown when estimated MPA-AUC0-12h was compared with measured MPA-AUC0-12h, and the range of coefficient of determination (r2) was from 0.479 to 0.936. The model based on MPA pharmacokinetic parameters C1h, C2h, C6h, and C8h had the best ability to predict measured MPA-AUC0-12h, with the best coefficient of determination (r2=0.936), the excellent prediction bias (2.18%), the best prediction precision (5.11%), and the best prediction variation (2SD=+/-7.88 mg.h/L). However, the model based on MPA pharmacokinetic sampling time points C1h, C2h, and C4h was more suitable when concerned with clinical convenience, which had shorter sampling interval, an excellent coefficient of determination (r2=0.795), an excellent prediction bias (3.48%), an acceptable prediction precision (14.37%), and a good prediction variation (2SD=+/-13.23 mg.h/L). Measured MPA-AUC0-12h could be best predicted by using MPA pharmacokinetic parameters C1h, C2h, C6h, and C8h. The model based on MPA pharmacokinetic parameters C1h, C2h, and C4h was more feasible in clinical application.

Variability of mycophenolate mofetil trough levels in stable kidney transplant patients

Great interindividual variability in the pharmacokinetics of mycophenolate mofetil (MMF) exists among kidney transplanted patients. The within-patient variability in stable transplanted patients is not well established. We performed 258 determinations of trough MMF levels in 86 stable transplant patients without hematological or gastrointestinal toxicity after at least year of a functioning kidney and a fixed dose of MMF. We examined the within-patient variability of levels related with clinical factors (age, gender, underlying cause of kidney failure, time since transplant, associated immunosuppression, and MMF dose) and analytical factors (serum creatinine, proteinuria, hemoglobin). Trough MMF levels were 3.6 mg/L, percentile (Pc) 25 1.6 mg/L, Pc 75 4.4 mg/L with intraindividual variability median of 65% (Pc 25 14%, Pc 75 79%). For the data analysis a variation of 14% was chosen, which corresponded to the 25th percentile. We did not observed differences between patients with variation below or above the Pc 25 in age, gender, underling cause of kidney failure, basal MMF levels, and MMF dose. Patients with greater variations showed significantly higher serum creatinine and proteinuria values than the others (1.84 +/- 0.54 vs 1.46 +/- 0.44 mg/dL and 0.45 +/- 0.42 vs 0.19 +/- 0.14 g/L; P < .05). Therefore, great within-patient variability in trough MMF levels was associated with poor kidney function and proteinuria.

Individualized mycophenolate mofetil dosing based on drug exposure significantly improves patient outcomes after renal transplantation

Efficacy and safety of mycophenolate mofetil (MMF) may be optimized with individualized doses based on therapeutic monitoring of its active metabolite, mycophenolic acid (MPA). In this 12-month study, 137 renal allograft recipients from 11 French centers receiving basiliximab, cyclosporine A, MMF and corticosteroids were randomized to receive either concentration-controlled doses or fixed-dose MMF. A novel Bayesian estimator of MPA AUC based on three-point sampling was used to individualize doses on posttransplant days 7 and 14 and months 1, 3 and 6. The primary endpoint was treatment failure (death, graft loss, acute rejection and MMF discontinuation). Data from 65 patients/group were analyzed. At month 12, the concentration-controlled group had fewer treatment failures (p = 0.03) and acute rejection episodes (p = 0.01) with no differences in adverse event frequency. The MMF dose was higher in the concentration-controlled group at day 14 (p < 0.0001), month 1 (p < 0.0001) and month 3 (p < 0.01), as were median AUCs on day 14 (33.7 vs. 27.1 mg*h/L; p = 0.0001) and at month 1 (45.0 vs. 30.9 mg*h/L; p < 0.0001). Therapeutic MPA monitoring using a limited sampling strategy can reduce the risk of treatment failure and acute rejection in renal allograft recipients 12 months posttransplant with no increase in adverse events.

Liquid chromatographic determination of mycophenolic acid and its metabolites in human kidney transplant plasma: pharmacokinetic application

BACKGROUND AND OBJECTIVE

Difference in the hydrophilic properties of mycophenolic acid metabolites makes it technically difficult to simultaneously determine their plasma levels in one analytical run. Therapeutic drug monitoring (TDM) for MPA ensures adequate MPA exposure levels to both prevent rejection and avoid related toxicity. One measure limitation for TDM for MPA is the availability of simple, rapid and reproducible method for determination of MPA derivatives.

METHOD

Herein we report a single method to measure MPA and its metabolites using a gradient elution system in less than 10 min. We further tested applicability of our method in both stable and unstable renal transplant recipients with a wide range of levels.

RESULTS

Intra- and inter-day imprecision were less than 8% and 10%, respectively. Accuracy of the estimated concentrations ranges from 90% to 108%.

CONCLUSION

Collectively these data show that the new method is reasonably accurate and precise for the simultaneous determination of MPA and its metabolites in human plasma.

Safety considerations with mycophenolate sodium

Following 10 years of clinical use of mycophenolate mofetil (MMF), a prodrug of mycophenolic acid, the FDA has approved enteric-coated mycophenolate sodium (EC-MPS). EC-MPS was developed to reduce the upper-gastrointestinal (GI) effects of MMF. Unlike oral MMF, where absorption starts in the stomach, EC-MPS releases MPA in the small intestine. Along with the pharmacology and pharmacokinetics, three randomized, controlled clinical trials in solid-organ transplantation, comparing MMF and EC-MPS, are reviewed. Disappointingly, EC-MPS was similar to MMF in efficacy and safety and did not significantly improve the GI side effects. Moreover, bioequivalence dosing has only been established with concomitant ciclosporin. The pharmacokinetic characteristics must be studied in greater detail. EC-MPS is a safe and effective immunosuppressive agent approved for use in the prevention of acute rejection after renal transplantation. However, the anticipated improvement of GI side effects has not been forthcoming.

Mycophenolate Mofetil Levels in Stable Kidney Transplant Recipients

The usefulness of mycophenolate mofetil (MMF) levels in stable kidney transplant patients is not well known. We measured MMF trough levels in 137 adult kidney recipients with more than 1 year of stable graft function. The MMF dose was adjusted according to hematological or gastrointestinal toxicity, it was 500 mg in 22 (16%) patients; 750 mg in 22 (16%); 1000 mg in 69 (50.5%); 1500 mg in 15 (11%); and 2000 mg in 9 (6.5%). We analyzed the total dose, virgule dose/kg, and MMF levels in relation to efficacy parameters (creatinine, proteinuria) and hematological toxicity (erythrocytes, leukocytes, and platelets) at the time of MMF level determinations and 3 months thereafter. Statistical analyses were performed with SSPS 12.0, including sensitivity and specificity analyses by ROC. Mean MMF levels were 3.68 mg/L (Pc25, 1.6-Pc75, 4.4 mg/L) with significant differences according to dose (P < .001). Trough MMF levels did not have discriminatory capacity in the area under the ROC for anemia, renal failure, or proteinuria at the time of determination or 3 months later. The percentage of patients without proteinuria was high among patients with MMF levels between 1.6 and 4.4 mg/L. The MMF levels were low in patients who had a major increase in creatinine (1.6 vs 3.8 mg/L, P < .05). In stable renal transplant patients the levels of MMF were related to the administered dose, and they are higher than those previously described in patients with less than a year follow-up with a functioning kidney. They did not have discriminatory value at the time of determination or 3 months later. Nevertheless, low MMF levels could help recognize patients at risk of developing chronic nephropathy.

Lack of an Effect of Oral Iron Administration on Mycophenolic Acid Pharmacokinetics in Stable Renal Transplant Recipients

STUDY OBJECTIVES

To determine if coadministration of polysaccharide iron complex and slow-release ferrous sulfate alter the absorption of mycophenolic acid (MPA), and to examine the potential influence of dosing relative to mycophenolate mofetil (MMF) administration and the effect of immediate- versus sustained-release iron products on the steady-state pharmacokinetics of MPA.

DESIGN

Prospective, open-label, three-phase, crossover, steady-state pharmacokinetic study.

SETTING

National Institutes of Health-sponsored General Clinical Research Center at a university medical center.

PATIENTS

Twelve adult (mean age 50 yrs) renal transplant recipients who were receiving concomitant iron and MMF maintenance therapy.

INTERVENTION

Oral iron therapy was coadministered with MMF on days -6-0, MMF was administered alone on days 1-8 (control phase), then oral iron therapy was administered 2 hours after MMF administration on days 9-16.

MEASUREMENTS AND MAIN RESULTS

Baseline demographics, concurrent drug regimens, and clinical laboratory values were assessed. Blood samples were obtained at baseline and at 1, 2, 3, 4, 6, 8, and 12 hours after MMF administration on days 0, 8, and 16. The MPA levels were measured by high-performance liquid chromatography. We found no significant differences in the dose-standardized area under the concentration-time curve from 0-12 hours (AUC(0-12)) for MPA between the control phase (39.66 +/- 8.70 mg mg x hr/L) and the concomitant ferrous sulfate or dose-separated ferrous sulfate (37.56 +/- 9.95 or 32.84 +/- 8.43 mg x hr/L, respectively, p>0.05) phases. Dose-standardized AUC(0-12) values for MPA did not significantly differ after the concomitant administration of polysaccharide iron complex from that of the control phase (48.46 +/- 9.68 and 43.80 +/- 9.46 mg x hr/L, respectively, p=0.065). However, the AUC(0-12) for MPA significantly increased when polysaccharide iron complex was administered 2 hours after MMF (53.41 +/- 11.75 mg x hr/L, p=0.012). Maximum concentrations and times to reach maximum concentrations remained consistent across all study phases in each arm of the trial (p>0.05).

CONCLUSION

Multiple doses of iron therapy-slow-release ferrous sulfate, or polysaccharide iron complex-did not significantly reduce systemic exposure to MMF, as measured by using AUC(0-12) values.

The Impact of Renal Allograft Function on Exposure and Elimination of Mycophenolic Acid (MPA) and Its Metabolite MPA 7-O-glucuronide

BACKGROUND

Previous studies have shown that total-body clearance of mycophenolic acid (MPA) is increased and total MPA exposure decreased in renal allograft recipients with severe renal dysfunction. In contrast to these studies, other studies have associated renal impairment with higher MPA exposure. The reason for these inconsistencies is not clear.

METHODS

In 120 renal allograft recipients with stable graft function and treated with a combination of mycophenolate mofetil, tacrolimus, and corticosteroids, clinical determinants of exposure to total MPA and its glucuronide metabolite MPA 7-O-glucuronide (MPAG) were investigated in a multivariate regression model at 3 (n=118) and 12 (n=63) months after transplantation.

RESULTS

Almost 50% of total MPA exposure could be explained by the final model, in which proteinuria, glomerular filtration rate, diabetes mellitus, and the mycophenolate mofetil dose were independent determinants of total MPA exposure. Lower glomerular filtration rate (GFR) was independently associated with higher MPA exposure both at 3 and 12 months after transplantation. GFR, alanine aminotransferase, and serum albumin levels and mycophenolate mofetil dose explained 69% of total MPAG exposure variability.

CONCLUSION

In stable renal recipients, total MPA exposure negatively associates with renal function, through accumulation of both MPA and MPAG in patients with moderately reduced renal allograft function. This is in contrast to severe graft dysfunction, where MPA clearance is higher due to increased free fraction of MPA, as shown in previous studies. The duality in the effect of graft function on MPA pharmacokinetics is of clinical importance, adjusting mycophenolate mofetil dose according to renal function might help to avoid side effects and improve efficacy.

Pharmacokinetics of enteric-coated mycophenolate sodium in stable liver transplant recipients

INTRODUCTION

Mycophenolate mofetil (MMF) is one of the major immunosuppressive agents used in liver transplantation recipients. In an attempt to mitigate one of the most common side effects of MMF (gastrointestinal symptoms), enteric-coated mycophenolate sodium (EC-MPS) was developed. In this study, we report the pharmacokinetic profile of EC-MPS in stable liver transplantation recipients administered a single 720 mg dose.

METHODS

Liver transplantation recipients more than one yr after transplantation were administered a single dose of 720 mg EC-MPS after which blood levels of MPA were measured at frequent intervals using a specific and validated LC-MS/MS assay.

RESULTS

The characteristics of the 21 patients studied were: mean age was 55.9 yr, 13 were female, eight had hepatitis C, and 14 were on tacrolimus. The mean apparent half-life of MPA was 5.3 +/- 4.3 h, (1.0-15.7). Mean t(max) was 2.4 +/- 1.1 h (1.0-5.0). The mean area-under-curve was 45.3 +/- 23.1 microg-h/mL (17.3-90.0). Trough level concentrations (C(12 h)) showed large inter-individual variability (0-9.2 microg/mL). There was no difference in any of the pharmacokinetic parameters relative to: gender, HCV, administration of tacrolimus vs. cyclosporine or type of biliary anastomosis.

CONCLUSIONS

There is a wide variation in pharmacokinetic parameters in stable, long-term liver transplantation recipients receiving a single dose of EC-MPS. These data suggest that therapeutic drug monitoring with EC-MPS may have limited utility in liver transplantation recipients.

Pharmacokinetics of mycophenolic acid and estimation of exposure using multiple linear regression equations in Chinese renal allograft recipients

OBJECTIVES

To investigate the pharmacokinetics of mycophenolic acid (MPA) in Chinese adult renal allograft recipients, and to generate the validated model equations for estimation of the MPA area under the plasma concentration-time curve from 0 to 12 hours (AUC(12)) with a limited sampling strategy.

PATIENTS AND METHODS

The pharmacokinetics in 75 Chinese renal allograft recipients treated with mycophenolate mofetil 2 g/day in combination with cyclosporin and corticosteroids were determined. The MPA concentration was assayed by high-performance liquid chromatography at pre-dose (C(0)) and at 0.5 (C(0.5)), 1 (C(1)), 1.5 (C(1.5)), 2 (C(2)), 4 (C(4)), 6 (C(6)), 8 (C(8)), 10 (C(10)) and 12 (C(12)) hours after dosing on day 14 post-transplant. Patients were randomly divided into: (i) a model group (n = 50) to generate the model equations by multiple stepwise regression analysis for estimation of the MPA AUC by a limited sampling strategy; and (ii) a validation group (n = 25) to evaluate the predictive performance of the model equations.

RESULTS

The mean MPA AUC(12) was 52.97 +/- 15.09 mg . h/L, ranging from 24.0 to 102.3 mg . h/L. The patient's age and serum albumin level had a significant impact on the MPA AUC(12). The correlation between the pre-dose MPA trough level (C(0)) and the MPA AUC(12) was poor (r(2) = 0.02, p = 0.33). Model equations 7 (MPA AUC(12) = 14.81 + 0.80 . C(0.5) + 1.56 . C(2) + 4.80 . C(4), r(2) = 0.70) and 11 (MPA AUC(12) = 11.29 + 0.51 . C(0.5) + 2.13 . C(2) + 8.15 . C(8), r(2) = 0.88) were selected for MPA AUC calculation in Chinese patients, resulting in good agreements between the estimated MPA AUC and the full MPA AUC(12), with a mean prediction error of +/-10.1 and +/-6.9 mg . h/L, respectively.

CONCLUSION

In Chinese renal allograft recipients, MPA pharmacokinetics manifest substantial interindividual variability, and the MPA AUC(12) tends to be higher than that in Caucasian patients receiving the same dose of mycophenolate mofetil. Two validated model equations with three sampling timepoints are recommended for MPA AUC estimation in Chinese patients.

Plasma concentrations of mycophenolic acid acyl glucuronide are not associated with diarrhea in renal transplant recipients

The aim of this study was to determine whether plasma concentrations of the acyl (AcMPAG) and phenolic (MPAG) glucuronide metabolites of mycophenolic acid (MPA) were related to diarrhoea in renal transplant patients on mycophenolate mofetil (MMF) with cyclosporine (CsA) or tacrolimus (TCL). Blood samples (0, 30, 120 min) were taken at days 3, 10, week 4, months 3, 6 and 12 for determination of MPA, MPAG and AcMPAG. MPA-AUC was estimated using validated algorithms. Two hour AUCs were calculated for MPAG and AcMPAG. Immunosuppressive therapy consisted of CsA/MMF (n= 110) and of TCL/MMF (n= 180). In 70/290 (24%) patients 86 episodes of diarrhoea were recorded during 12 months. Significantly more patients on TCL (31.1%) suffered from diarrhea compared to CsA (12.7%). MMF dose, MPA-AUC and the 2 h AUCs of MPAG and AcMPAG did not differ between patients with and without diarrhoea. Plasma AcMPAG and MPAG concentrations were substantially higher in patients on CsA compared with TCL, while MPA-AUC was lower in the former group. These data support the concept that CsA inhibits the biliary excretion of MPAG and AcMPAG, thereby potentially reducing the risk of intestinal injury through enterohepatic recycling of MPA and its metabolites.

Therapeutic drug measurement of mycophenolic acid derivatives in transplant patients

INTRODUCTION

Mycophenolic acid, the active metabolite of the prodrug mycophenolate mofetil, is widely used as an immunosuppressive agent in transplant patients for the prophylaxis of acute rejection. Recent prospective trials suggested the need for therapeutic drug monitoring, which raises the necessity to acquire accurate methods to measure MPA and its metabolites.

OBJECTIVE

Present an overview of the reasons to monitor MPA and its metabolites as well as a review of the currently available methods for their determination.

METHODS

Articles published from January 1992 to December 2006 were reviewed.

RESULTS

Most of the cited references use either chromatographic or immunoassay techniques. Basic information about biological samples used for the analysis, sample preparation, stationary phase, mobile phase, detection mode and validation data are discussed. Current information suggests the feasibility to set up method(s) to monitor MPA and its metabolites in most centers.

Monitoring of inosine monophosphate dehydrogenase activity as a biomarker for mycophenolic acid effect: potential clinical implications

Mycophenolic acid (MPA) is a reversible inhibitor of inosine monophosphate dehydrogenase (IMPDH) and, in combination with other immunosuppressive drugs, effectively inhibits rejection in solid organ transplant recipients. MPA has a relatively narrow therapeutic window and exhibits wide inter- and intrapatient pharmacokinetic (PK) variability. This has stimulated the use of therapeutic drug monitoring as a strategy to tailor the MPA exposure to each patient's individual needs. Despite increasing therapeutic drug monitoring use, PK-assisted dosing is not universally adopted in part because of MPA's complex PK behavior. Targeting inosine monophosphate IMPDH activity as a surrogate pharmacodynamic (PD) marker of MPA-induced immunosuppression may allow for increased precision when used in an integrated PK-PD fashion, providing a more accurate assessment of efficacy and aid in limiting toxicity. IMPDH activity displays wide interpatient variability but relatively small intrapatient variability even after long-term administration of MPA. The advent of calcineurin and corticosteroid-sparing regimens necessitates more patient-specific PK-PD parameters, which can be used throughout the posttransplant period to optimize MPA exposure and immediate and long-term graft and patient outcomes. Quantification of IMPDH posttransplant may serve as a stable, surrogate PD marker of MPA-induced immunosuppression when combined with current PK and monitoring strategies.

Pharmacokinetics, safety, and efficacy of mycophenolate mofetil in combination with sirolimus or ciclosporin in renal transplant patients

AIMS

To compare the pharmacokinetics of mycophenolic acid (MPA) and its metabolite (MPAG) when mycophenolate mofetil (MMF) is administered in combination with sirolimus or ciclosporin (CsA) in renal allograft recipients. Safety and efficacy (biopsy-proven acute rejection (BPAR)) were also assessed.

METHODS

Patients (n = 45) were randomized 2 : 1 to receive treatment with sirolimus (n = 30; dosed to maintain trough concentrations of 10-25 ng ml(-1) until week 8, and then 8-15 ng ml(-1) thereafter) or CsA (n = 15; administered as per centre practice) both in combination with daclizumab, oral MMF and corticosteroids. Pharmacokinetic assessments were performed at day 7, week 4, and months 3 and 6 post-transplant. The primary endpoint was the AUC(0,12 h) for MPA and MPAG. The pharmacokinetics of sirolimus were also assessed.

RESULTS

MPA exposure was 39-50% lower (month 6 mean AUC(0,12 h) (95%CI): 40.4 (33.8, 47.0) vs. 68.5 (54.9, 82.0) microg ml(-1) h) and MPAG exposure was 25-52% higher (722 (607, 838) vs. 485 (402, 569) microg ml(-1) h at month 6) in the presence of CsA compared with sirolimus across visits. BPAR was 40.0% with sirolimus and 13.3% with CsA. The incidence of hypertension, tremors and hirsutism was higher with CsA than with sirolimus, while the incidence of diarrhoea, hyperlipidaemia and impaired wound closure was higher with sirolimus. No deaths, malignancies or graft losses were reported.

CONCLUSIONS

Co-administration of sirolimus with MMF led to greater MPA exposure, but lower MPAG exposure, than co-administration with CsA. As rejection rates were higher in the absence of CsA, further study of calcineurin inhibitor-free regimens is required before general recommendations can be made.

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

The delayed release of mycophenolic acid (MPA) from enteric-coated mycophenolate sodium (EC-MPS) may lead to different MPA predose (C0) levels compared with mycophenolate mofetil (MMF). A post hoc analysis was performed on MPA morning predose values assessed in 88 maintenance renal transplant patients from three studies converted from MMF (1000 mg twice a day) to equimolar EC-MPS (720 mg twice a day) or vice versa, both in combination with cyclosporine. The median MPA predose level was approximately 30% higher when patients received EC-MPS (2.40 microg/mL; range, 0.49-39.30 microg/mL) compared with MMF (1.83 microg/mL; range, <0.1-12.80 microg/mL). Rare cases (3.0%) of high MPA C0 levels 15 microg/mL or greater were observed with EC-MPS consistent with a very prolonged release of MPA from this formulation. Both EC-MPS and MMF exhibited a poor correlation between MPA C0 levels and exposure as assessed by MPA area under the curve. Physicians targeting a certain MPA predose level have to be aware of the higher morning C0 levels with EC-MPS, whereas the overall MPA exposure is not different to MMF.

Therapeutic drug monitoring of mycophenolic acid: does it improve patient outcome?

Treatment with the immunosuppressive agent mycophenolate mofetil (MMF) decreases the risk of rejection after renal transplantation and improves graft survival compared with azathioprine. The exposure to the active metabolite mycophenolic acid (MPA) is correlated to the risk of developing acute rejection. The interpatient variability in exposure of MPA is wide relative to the proposed therapeutic window of the MPA AUC(0 12) (30 - 60 mg.h/l). The pharmacokinetics of MPA are influenced by patient characteristics such as gender, time after transplantation, serum albumin concentration, renal function, comedication and pharmacogenetic factors. Therapeutic drug monitoring is likely to reduce inter-patient variability. Limited sampling strategies are used to predict the full AUC(0 12). Three prospective randomised studies compared concentration controlled MMF therapy to a fixed-dose regimen. Preliminary outcomes of these studies showed conflicting results and longer follow up is needed to further clarify the role of therapeutic drug monitoring in increasing the therapeutic potential of MMF.

Pharmacokinetic and pharmacodynamic comparison of enteric-coated mycophenolate sodium and mycophenolate mofetil in maintenance renal transplant patients

The aim of this single-center crossover substudy was to assess pharmacokinetics and pharmacodynamics [inosine 5'-monophosphate dehydrogenase (IMPDH) activity] of enteric-coated mycophenolate sodium (EC-MPS) and mycophenolate mofetil (MMF) at steady-state conditions. Stable maintenance renal transplant patients on 1 g MMF b.i.d. participating in a double-blind, multicenter study, were randomized to receive EC-MPS (720 mg b.i.d.) or continue receiving MMF (1000 mg b.i.d.) for 12 months. Thereafter, all patients (n = 18) received 720 mg EC-MPS b.i.d. Area under the plasma mycophenolic acid (MPA) concentration-time curve with EC-MPS (57.4 +/- 15.0 microg h/mL) fulfilled bioequivalence criteria (geometric mean 0.98 (90% CI: 0.87-1.11) compared to MMF (58.4 +/- 14.1 microg h/mL). Consistent with the delayed release characteristics of EC-MPS, peak MPA concentration (geometric mean 0.89; 90% CI: 0.70-1.13) occurred approximately 0.5 h later (p < 0.05) and predose MPA levels (geometric mean 2.10; 90% CI: 1.51-2.91) were higher and more variable, not fulfilling bioequivalence criteria. IMPDH activity inversely followed MPA concentrations and was inhibited to a similar degree (approximately 85%) by both formulations. The calculated value for 50% IMPDH inhibition was identical for both drugs. In conclusion, equimolar doses of EC-MPS and MMF produce equivalent MPA exposure, while the delayed release formulation of EC-MPS exhibits more variable predose levels and T(max). Overall, IMPDH activity reflected MPA pharmacokinetics.

One-year results with extended-release tacrolimus/MMF, tacrolimus/MMF and cyclosporine/MMF in de novo kidney transplant recipients

Once-daily tacrolimus extended-release formulation (Prograf XL, formerly referred to as MR or MR4) was compared with the twice-a-day tacrolimus formulation (TAC) and cyclosporine microemulsion (CsA), all administered in combination with mycophenolate mofetil (MMF), corticosteroids and basiliximab induction, in a phase 3, randomized (1:1:1), open-label trial in 638 de novo kidney transplant recipients. In combination with MMF and corticosteroids, XL had an efficacy profile comparable to TAC and CsA. XL/MMF and TAC/MMF were statistically noninferior at 1-year posttransplantation to CsA/MMF for the primary efficacy endpoint, efficacy failure (death, graft loss, biopsy-confirmed acute rejection (BCAR) or lost to follow-up). One-year patient and graft survival were 98.6% and 96.7% in the XL/MMF group, 95.7% and 92.9% in TAC/MMF group and 97.6% and 95.7% in CsA/MMF group. The safety profile of XL in comparison with CsA was similar to that observed with TAC in this study and consistent with previously published reports of TAC in comparison with CsA. The results support the safety and efficacy of tacrolimus in combination with MMF, corticosteroids and basiliximab induction, as well as XL as a safe and effective once-daily dosing alternative.

Concentrations of Mycophenolic Acid and Glucuronide Metabolites Under Concomitant Therapy With Cyclosporine or Tacrolimus

Mycophenolate mofetil [MMF, the prodrug of mycophenolic acid (MPA)] is usually administered at double doses with cyclosporine than with tacrolimus because it is believed that MPA exposure is lower during cyclosporine therapy. This study aimed to compare 12 hour, steady-state concentration-time profiles of MPA and its phenol- and acyl-glucuronide metabolites (MPAG and AcMPAG, respectively) in stable kidney transplant recipients maintained either on cyclosporine (n = 12) or tacrolimus (n = 12). During the absorption phase in the cyclosporine group, dose-normalized concentrations of total and free MPA were significantly higher but the overall area under the concentration-time curve (AUC0-12) was not significantly different. Additionally, exposure to AcMPAG was higher in the cyclosporine group (P < 0.05). Ten of 12 patients in the cyclosporine group were on ketoconazole therapy; however, the exposure to MPA or MPAG was not different when MMF was given orally to Sprague-Dawley rats with or without ketoconazole. In conclusion, cyclosporine modulates the disposition of MPA and metabolites differently from tacrolimus; however, patients on cyclosporine may not require double doses of MMF to achieve the same exposure.

The Magnitude and Time Course of Changes in Mycophenolic Acid 12-Hour Predose Levels During Antibiotic Therapy in Mycophenolate Mofetil-Based Renal Transplantation

There is increasing evidence that monitoring predose plasma levels of mycophenolic acid (MPA) is of benefit in renal transplant recipients treated with mycophenolate mofetil (MMF). Concomitant treatment with oral antibiotics leads to a 10% to 30% reduction in MPA area under the curve (AUC)0-12, probably by reducing enterohepatic recirculation (EHR). Because of the timing of EHR (6 to 12 hours postdose), the magnitude of predose MPA level reduction may be disproportionately larger than that of AUC0-12. However, changes in predose MPA levels and the time course over which these changes occur and resolve during antibiotic treatment have not been studied. The purpose of this study was to define the extent and time course of MPA predose level reduction during antibiotic therapy. A total of 64 MMF-treated renal transplant recipients (with tacrolimus cotherapy) were prospectively studied. Clinically indicated cotherapy with either oral ciprofloxacin or amoxicillin with clavulanic acid resulted in a reduction in 12 hour predose MPA level to 46% of baseline within 3 days of antibiotic commencement. No demographic or biochemical variables were associated with the magnitude of MPA level reduction. No further fall in MPA level was seen by day 7, but MPA levels recovered spontaneously to 79% of baseline after 14 days of antibiotics. Levels normalized within 3 days of antibiotic cessation. No changes in daily MMF dose (normalized for body weight) were made during antibiotic treatment. This data should help the clinician to recognize the extent of MPA predose level reduction during antibiotic therapy, and to avoid inappropriate MMF dose escalation and potential risk of toxicity.

Time-dependent clearance of mycophenolic acid in renal transplant recipients

AIMS

Pharmacokinetic studies of the immunosuppressive compound mycophenolic acid (MPA) have shown a structural decrease in clearance (CL) over time after renal transplantation. The aim of this study was to characterize the time-dependent CL of MPA by means of a population pharmacokinetic meta-analysis, and to test whether it can be described by covariate effects.

METHODS

One thousand eight hundred and ninety-four MPA concentration-time profiles from 468 renal transplant patients (range 1-9 profiles per patient) were analyzed retrospectively by nonlinear mixed effect modelling. Sampling occasions ranged from day 1-10 years after transplantation.

RESULTS

The pharmacokinetics of MPA were described by a two-compartment model with time-lagged first order absorption, and a first-order term for time-dependent CL. The model predicted the mean CL to decrease from 35 l h(-1) (CV = 44%) in the first week after transplantation to 17 l h(-1) (CV = 38%) after 6 months. In a covariate model without a term for time-dependent CL, changes during the first 6 months after transplantation in creatinine clearance from 19 to 71 ml min(-1), in albumin concentration from 35 to 40 g l(-1), in haemoglobin from 9.7 to 12 g dl(-1) and in cyclosporin predose concentration from 225 to 100 ng ml(-1) corresponded with a decrease of CL from 32 to 19 l h(-1). Creatinine clearance, albumin concentration, haemoglobin and cyclosporin predose concentration explained, respectively, 19%, 12%, 4% and 3% of the within-patient variability in MPA CL.

CONCLUSIONS

By monitoring creatinine clearance, albumin concentration, haemoglobin and cyclosporin predose concentration, changes in MPA exposure over time can be predicted. Such information can be used to optimize therapy with mycophenolate mofetil.

Mycophenolic acid trough level monitoring in solid organ transplant recipients treated with mycophenolate mofetil: association with clinical outcome

BACKGROUND

Mycophenolate mofetil (MMF) is widely and successfully used in immunosuppressive regimens for the prophylaxis of organ rejection following transplantation. Conventionally, it is administered at a fixed dose without serial measurements of plasma concentrations of mycophenolic acid (MPA), the active metabolite. Recently, there has been an increased interest in therapeutic drug monitoring (TDM) of MMF therapy to optimize the benefit/risk index of the drug. Predose trough samples of MPA are considered most convenient and economic, thereby allowing an increased use of TDM in the transplant setting. However, the added value of TDM for MMF therapy is still under debate.

OBJECTIVE

This paper reviews (based on a systematic PubMed and EMBASE search, 1995-June 2006) the current evidence of the usefulness and clinical relevance of MPA trough level monitoring during MMF therapy in solid organ transplantation.

FINDINGS AND CONCLUSIONS

Based on data available in the public domain, the contribution of MPA trough level monitoring during MMF therapy in solid organ transplant recipients remains unproven. Available studies have limitations and report conflicting results. There is a lack of prospective randomized trials, particularly in pediatric renal transplant recipients and in cardiac and liver transplantation. While there is a suggestion that there may be a relationship between efficacy and MPA trough levels, the majority of studies showed no correlation between MPA plasma concentrations and adverse effects. Based on current evidence, the adherence to presently recommended target ranges for MPA troughs in solid organ transplantation cannot assure an improved clinical outcome with MMF therapy. Whether MPA trough level monitoring leads to improved efficacy and less toxicity is currently subject to a large randomized trial; final results are eagerly awaited.

A comparison of measured trough levels and abbreviated AUC estimation by limited sampling strategies for monitoring mycophenolic acid exposure in stable heart transplant patients receiving cyclosporin A-containing and cyclosporin A-free immunosuppressive regimens

BACKGROUND

Mycophenolate mofetil (NIMF) pharmacokinetics vary widely, and enterohepatic recirculation of the drug and its metabolites may be altered by concurrently administered immunosuppressants, including the widely used agent cyclosporin A (CsA). A reliable method of achieving effective and well-tolerated levels of NIMF-based immunosuppression would be of eminent interest.

OBJECTIVE

This study compared the use of measured mycophenolic acid (MPA) trough levels (C0) and abbreviated AUC estimation by limited-sampling strategies for monitoring MPA exposure in stable heart transplant recipients (>1 year after transplantation) receiving a CsA-containing or CsA-free immunosuppressive regimen.

METHODS

The treatment groups were receiving chronic maintenance immunosuppressive regimens consisting of either CsA/MMF or rapamycin (RAPA)/MMF. An additional subgroup of patients was switched from the CsA-containing regimen to the RAPA-containing regimen. Fasting venous blood samples were obtained before dosing and at 40, 75, 120, and 240 minutes after administration of the morning dose of MME The validated Emit assay was used to measure MPA plasma concentrations. Dose adjustment of AUCs was performed by dividing the AUC by the morning NIMF dose in grams. Cmax after administration of the morning dose was determined from available MPA data points using curve-fitting analysis. The increase to Cmax (Cmax-C0) was calculated, and dose adjustment was performed as before. Abbreviated 12-hour MPA AUCs were estimated using a limited-sampling strategy (before dosing and 30 and 120 minutes after dosing) based on high-performance liquid chromatography data. Adverse events were monitored during routine follow-up visits.

RESULTS

The study included 47 patients receiving CsA/MMF, 15 receiving RAPA/MMF, and 9 who were switched from CsA/MMF to RAPA/MME The population included 55 men and 7 women, with a mean age of 58.94 years and a mean weight of 81.85 kg. The only significant differences in baseline clinical characteristics between groups were the mean number of years since heart transplantation (3.62 CsA/MMF vs 8.53 RAPA/MMF; P<0.01) and the proportions of patients still receiving corticosteroids (44.7% vs 13.3%, respectively; P<0.01). Reported adverse events were generally mild, including leukopenia (8.1%), diarrhea (6.5%), and abdominal pain (4.8%), and did not require drug discontinuation. In patients receiving CsA/MMF, MPA AUCs ranged from 19.67 to 81.80 mg/h.L (mean [SD], 41.92 [14.14] mg/h.L). MPA Co levels were poorly correlated with total AUC (r2=0.36). MPA Co levels of 0.5 and 1.6 mg/L were correlated with AUCs of <30 and <40 mg/h.L, respectively. In patients receiving RAPA/MMF, MPA AUCs ranged from 34.40 to 87.60 mg/h.L (mean, 51.07 [15.80] mg/h.L). The correlation between Co and total AUC was better than in the CsA/MMF group (r2=0.61). MPA C0 levels of 1.0 and 2.3 mg/L were correlated with AUCs of 30 and 40 mg/h.L, respectively. Statistically significant differences between RAPA/MMF and CsA/MMF were noted in the mean MMF dosage (1.90 [0.71] vs 2.87 [0.78] g/d, respectively; P<0.001), the mean dose-adjusted MPA AUC (60.95 [27.42] vs 31.92 [16.12] mg/h.L.g MMF; P<0.001), and mean dose-adjusted MPA C0 levels (5.10 [3.41] vs 1.41 [0.95] mg/L.g; P<0.001). The dose-adjusted increase to Cmax after morning dosing was comparable between groups, and there was no difference in the frequency distribution of Cmax. In the group switched from the CsA-containing regimen to the RAPA-containing regimen, the changes in MMF dose, dose-adjusted AUC, and MPA C0 levels were similar to those in the CsA/MMF and RAPA/MMF groups.

CONCLUSIONS

In this comparison of measured MPA C0 levels and 12-hour MPA AUCs estimated by a limited-sampling strategy in stable heart transplant patients receiving chronic maintenance immunosuppressive therapy with CsA/MMF or RAPA/MMF, abbreviated AUC estimation predicted drug exposure more accurately than did measured C0 levels. Thus, MPA AUCs obtained by limited sampling may be useful in guiding clinical management and dosing. However, further study is required, including validation of these findings in clinical outcome studies.

Effects of gastric emptying on oral mycophenolic acid pharmacokinetics in stable renal allograft recipients

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

* Strategies that are more elaborate than measuring predose plasma concentrations are required for the therapeutic monitoring of mycophenolic acid (MPA). * Previous studies in healthy subjects and diabetes patients have suggested that MPA pharmacokinetics are influenced by gastric emptying, but this has not been demonstrated directly.

WHAT THIS STUDY ADDS

* This study has investigated the relationship between gastric emptying, measured directly (using the (14)C octanoate and (13)C glycine breath tests) and the steady-state plasma concentration-time profile of MPA. * Delayed gastric emptying was associated with a longer t(max) and lower C(max), but total exposure to MPA was not affected. * The findings suggest that it could be misleading to rely fully on short-term (<2 h) limited sampling strategies for MPA therapeutic monitoring in recipients with gastric emptying disorders, the latter occurring relatively frequently in solid organ transplantation.

AIM

To investigate the effect of gastric emptying on the pharmacokinetics of mycophenolic acid (MPA) in renal transplant patients.

METHODS

We assessed the effect of gastric emptying on the disposition of MPA in 27 stable renal allograft recipients at 2 years after transplantation. Gastric emptying was measured by the (14)C-octanoate and (13)C-glycine breath test.

RESULTS

Delayed gastric emptying was associated with a significantly longer MPA t(max)[1.0 (0.33-2.0) h vs. 0.5 (0.33-1.0) h; mean difference 0.39 h, 95% confidence interval (CI) 0.03, 0.75; P = 0.0289] and with a significant decrease in the maximum MPA concentration after dosing [10.6 (6.5-21.3) mg l(-1)vs. 20.1 (10.7-28.5) mg l(-1); mean difference 6.5 mg l(-1), 95% CI 2.1, 10.9; P = 0.0075]. Despite the substantial effect of delayed gastric emptying rates on MPA C(max) and t(max), total dose-interval exposure, measured by the MPA AUC(0-4), was not affected by the rate of gastric emptying [20.4 (13.9-43.0) mg h(-1) l(-1)vs. 22.4 (13.1-29.8) mg h(-1) l(-1)].

CONCLUSION

Delayed gastric emptying was associated with a slower absorption of MPA, a longer time to reach peak concentrations and lower maximum concentrations. These effects should be taken into account when validating limited (<2 h) sampling strategies to estimate total MPA exposure, which could be unreliable when monitoring patients with gastric emptying disorders.