Therapeutic drug monitoring of mycophenolate mofetil in transplantation

Concentration-controlled treatment of lupus nephritis with mycophenolate mofetil

Background:

Mycophenolate mofetil (MMF) has recently been established as a potent drug in maintenance treatment for lupus nephritis. However, there is no consensus on the optimal dosing regimen because of a high inter-individual variability of mycophenolic acid (MPA), the active metabolite of MMF. This retrospective study aimed to investigate the effect of an individualized dosing regimen through concentration-controlled treatment on MPA exposure and renal outcome in patients with lupus nephritis.

Methods:

Sixteen patients with lupus nephritis and treatment with low-dose intravenous cyclophosphamide followed by MMF were included. MPA area under the plasma concentration-time curve from 0 to 12 hours (MPA-AUC0–12) was assessed within a month after MMF initiation. After determination of MPA-AUC0–12, MMF doses were titrated to achieve a target MPA-AUC0–12 of 60–90 mg*h/l. After on average six months, MPA-AUC0–12 measures were repeated to assess the effect of dose adjustment.

Results:

One month after introducing MMF, MPA-AUC0–12 was low and showed a high inter-individual variability. Dose adjustment with a target MPA-AUC0–12 of 60–90 mg*h/l resulted in individualized MMF dosing, significantly higher MPA-AUC0–12 levels, and a non-significant reduction in variability of MPA-AUC0–12. Adverse effects were reported by 37.5% of patients, which resulted in a switch to azathioprine in two patients. There was no significant relationship between the occurrence of adverse effects and MPA-AUC0–12. At 12 months of follow-up 87.5% of patients had achieved either partial (18.7%) or complete (68.8%) remission.

Conclusion:

Concentration-controlled dose adjustments with a target MPA-AUC0–12 of 60–90 mg*h/l was associated with optimized MPA exposure and an excellent renal outcome at 12 months of follow-up in a small sample of SLE patients with lupus nephritis.

Monitoring of nonsteroidal immunosuppressive drugs in patients with lung disease and lung transplant recipients: American College of Chest Physicians evidence-based clinical practice guidelines

OBJECTIVES

Immunosuppressive pharmacologic agents prescribed to patients with diffuse interstitial and inflammatory lung disease and lung transplant recipients are associated with potential risks for adverse reactions. Strategies for minimizing such risks include administering these drugs according to established, safe protocols; monitoring to detect manifestations of toxicity; and patient education. Hence, an evidence-based guideline for physicians can improve safety and optimize the likelihood of a successful outcome. To maximize the likelihood that these agents will be used safely, the American College of Chest Physicians established a committee to examine the clinical evidence for the administration and monitoring of immunosuppressive drugs (with the exception of corticosteroids) to identify associated toxicities associated with each drug and appropriate protocols for monitoring these agents.

METHODS

Committee members developed and refined a series of questions about toxicities of immunosuppressives and current approaches to administration and monitoring. A systematic review was carried out by the American College of Chest Physicians. Committee members were supplied with this information and created this evidence-based guideline.

CONCLUSIONS

It is hoped that these guidelines will improve patient safety when immunosuppressive drugs are given to lung transplant recipients and to patients with diffuse interstitial lung disease.

Pharmacokinetics of free mycophenolic acid and limited sampling strategy for the estimation of area under the curve in liver transplant patients

Mycophenolate Mofetil (MMF) is widely used in preventing acute rejection in liver transplantation. Only free MPA (fMPA) can exert the pharmacological effect. In this study, we aimed to develop the new model which could be best fit to predict the fMPA area under the plasma concentration-time curve (AUC) by limited sampling strategy (LSS) in Chinese liver transplant patients. Fifty patients received MMF with the combination of tacrolimus. Free MPA concentrations were determined around day 7. Optimal subset regression analysis was used to establish the models for estimated fMPA AUC(0-12h). Three excellent better models were validated by Bootstrap analysis. Twenty-four models including four blood time point samplings were established. For the selected four models, 100% were successful and were not significantly different from the original dataset by Bootstrap analysis. The best model for prediction of fMPA AUC(0-12h) was by using C(1h), C(2h), C(4h) and C(6h). This model showed the minimal mean prediction error and the minimal mean absolute prediction error. In conclusion, the models for estimation of the fMPA AUC(0-12h) were established in liver transplant recipients and the best model for prediction of fMPA AUC was: estimated fMPA AUC=34.2+1.12C(1h)+1.29C(2h)+2.28C(4h)+3.95C(6h).

Monitoring of inosine monophosphate dehydrogenase activity and expression during the early period of mycophenolate mofetil therapy in de novo renal transplant patients

Measurement of inosine-monophosphate dehydrogenase (IMPDH) activity or gene expression was used as a further approach in pharmacokinetics (PK)/pharmacodynamic (PD)-guided mycophenolate mofetil (MMF) therapy. Forty-four de novo kidney transplant patients were enrolled; 35 of these completed the study, and were followed for 24 weeks for clinical status, PK parameters, IMPDH activity and IMPDH1/2 gene expression. IMPDH activity and expression were measured in peripheral blood mononuclear cells before transplant and at week 2,4,12 and 24, drawn before (t0) and 2 h (t2 h) after MMF administration. No significant correlation was found between IMPDH activity/expression and PK parameters. For both genes, significant enhancement in t2 h expression was observed, then decreases towards week 24 with a trend following steroid dosages. Seven patients experienced acute rejection (AR) and exhibited significantly higher pre-transplant expression of both IMPDH1 (median 3.42 vs. 0.84; p=0.0025), and IMPDH2 genes (135 vs. 104; p=0.0218) with respect to non-rejecting patients. A significant association was also found between pre-transplant IMPDH1 mRNA and haematological complications (p=0.032). This study suggests that high steroid dosages may influence IMPDH1/2 expression, hampering their use as a PD biomarker, particularly during the early post-transplant period. The measurement of pre-transplant levels of IMPDH1/2 may contribute to prediction of individual drug responsiveness to improve the clinical management of patients in MMF therapy.

Randomized trial comparing late concentration-controlled calcineurin inhibitor or mycophenolate mofetil withdrawal

BACKGROUND

Early calcineurin inhibitor (CNI) withdrawal with mycophenolate mofetil (MMF) has not become routine practice, due to concerns about excess acute rejection. Therapeutic drug monitoring may be advantageous when the CNI or MMF is withdrawn.

METHODS

This prospective, randomized, concentration-controlled withdrawal study enrolled 177 stable renal transplant recipients on maintenance CNI-based immunosuppression, combined with steroids and MMF. After the feasibility phase of the study, patients were randomized to MMF-withdrawal (target area under the time-concentration curve-cyclosporine: 3250 ng·hr/mL or tacrolimus: 120 ng·hr/mL) or CNI-withdrawal (target area under the time-concentration curve-mycophenolic acid: 75 μg·hr/mL).

RESULTS

The estimated glomerular filtration rate (modification of diet in renal disease) remained significantly better after CNI elimination (59.5±2.1 mL/min vs. 51.1±2.1 mL/min, P = 0.006) up to 3 years and resulted in less functional decline, including the subgroup with an estimated glomerular filtration rate less than 50 mL/min at baseline (P = 0.03). At 6 months, one patient in the MMF-withdrawal group (1.3%) and three in the CNI-withdrawal group (3.8%) experienced acute rejection (P = 0.62). The defined higher mycophenolic acid exposure was well tolerated.

CONCLUSION

These data indicate that with time the large majority of stable renal transplant recipients can be safely reduced to dual therapy with MMF or CNIs, applying concentration-controlled dosing. CNI-free patients, including those with moderate renal allograft dysfunction, have the benefit of improved renal function, whereas the risk of acute rejection after late withdrawal is low.

A possible simplification for the estimation of area under the curve (AUC₀₋₁₂) of enteric-coated mycophenolate sodium in renal transplant patients receiving tacrolimus

Enteric-coated mycophenolate sodium (EC-MPS) is widely used in renal transplantation. With a delayed absorption profile, it has not been possible to develop limited sampling strategies to estimate area under the curve (mycophenolic acid [MPA] AUC₀₋₁₂), which have limited time points and are completed in 2 hours. We developed and validated simplified strategies to estimate MPA AUC₀₋₁₂ in an Indian renal transplant population prescribed EC-MPS together with prednisolone and tacrolimus. Intensive pharmacokinetic sampling (17 samples each) was performed in 18 patients to measure MPA AUC₀₋₁₂. The profiles at 1 month were used to develop the simplified strategies and those at 5.5 months used for validation. We followed two approaches. In one, the AUC was calculated using the trapezoidal rule with fewer time points followed by an extrapolation. In the second approach, by stepwise multiple regression analysis, models with different time points were identified and linear regression analysis performed. Using the trapezoidal rule, two equations were developed with six time points and sampling to 6 or 8 hours (8hrAUC[₀₋₁₂exp]) after the EC-MPS dose. On validation, the 8hrAUC(₀₋₁₂exp) compared with total measured AUC₀₋₁₂ had a coefficient of correlation (r²) of 0.872 with a bias and precision (95% confidence interval) of 0.54% (-6.07-7.15) and 9.73% (5.37-14.09), respectively. Second, limited sampling strategies were developed with four, five, six, seven, and eight time points and completion within 2 hours, 4 hours, 6 hours, and 8 hours after the EC-MPS dose. On validation, six, seven, and eight time point equations, all with sampling to 8 hours, had an acceptable r with the total measured MPA AUC₀₋₁₂ (0.817-0.927). In the six, seven, and eight time points, the bias (95% confidence interval) was 3.00% (-4.59 to 10.59), 0.29% (-5.4 to 5.97), and -0.72% (-5.34 to 3.89) and the precision (95% confidence interval) was 10.59% (5.06-16.13), 8.33% (4.55-12.1), and 6.92% (3.94-9.90), respectively. Of the eight simplified approaches, inclusion of seven or eight time points improved the accuracy of the predicted AUC compared with the actual and can be advocated based on the priority of the user.

Large scale analysis of routine dose adjustments of mycophenolate mofetil based on global exposure in renal transplant patients

BACKGROUND

We report a feasibility study based on our large-scale experience with mycophenolate mofetil dose adjustment based on mycophenolic acid interdose area under the curve (AUC) in renal transplant patients.

METHODS

Between 2005 and 2010, 13,930 requests for 7090 different patients (outside any clinical trial) were posted by more than 30 different transplantation centers on a free, secure web site for mycophenolate mofetil dose recommendations using three plasma concentrations and Bayesian estimation.

RESULTS

This retrospective study showed that 1) according to a consensually recommended 30- to 60-mg·h/L target, dose adjustment was needed for approximately 35% of the patients, 25% being underexposed with the highest proportion observed in the first weeks after transplantation; 2) when dose adjustment had been previously proposed, the subsequent AUC was significantly more often in the recommended range if the dose was applied than not at all posttransplantation periods (72-80% vs. 43-54%); and 3) the interindividual AUC variability in the "respected-dose" group was systematically lower than that in the "not respected-dose" group (depending on the posttransplantation periods; coefficient of variation %, 31-41% vs 49-70%, respectively). Further analysis suggested that mycophenolic acid AUC should best be monitored at least every 2 weeks during the first month, every 1 to 3 months between months 1 and 12, whereas in the stable phase, the odds to be still in the 30- to 60-mg·h/L range on the following visit was still 75% up to 1 year after the previous dose adjustment.

CONCLUSION

This study showed that the monitoring of mycophenolate mofetil on the basis of AUC measurements is a clinically feasible approach, apparently acceptable by the patients, the nurses, and the physicians owing to its large use in routine clinics.

Inosine 5'-monophosphate dehydrogenase activity as a biomarker in the field of transplantation

Inosine 5'monophosphate dehydrogenase (IMPDH) is the rate limiting enzyme in the de novo synthesis of guanine nucleotides. The direct determination of target enzyme activity as a biomarker of mycophenolic acid (MPA) may help to estimate better the individual response to the immunosuppressant. However, the assessment of the clinical utility of this approach is limited by the diversity of the assay systems, which has not yet allowed the prospective assessment of this enzyme in larger patient cohorts. A recently validated and standardized assay allows the investigation of IMPDH activity in larger clinical studies. Although descriptive results from observational studies hold promise for a more individualized therapy in transplant medicine, more studies are needed to prospectively validate this approach.

Safety and efficacy of intensified versus standard dosing regimens of enteric-coated mycophenolate sodium in de novo renal transplant patients

BACKGROUND

Efficacy and safety of an intensified dosing (ID) regimen of enteric-coated mycophenolate sodium (EC-MPS), which achieves higher mycophenolic acid exposure early posttransplantation, were evaluated in comparison with a standard dosing (SD) regimen.

METHODS

In total, 128 de novo kidney transplant recipients treated with basiliximab induction, cyclosporine A, and steroids were randomized (1:1) to receive EC-MPS as SD (1440 mg/day; n=65) or ID (days 0-14: 2880 mg/day; days 15-42: 2160 mg/day; followed by 1440 mg/day; n=63). Efficacy parameters, safety, and tolerability were assessed over a 6-month study period. The primary endpoint was mean time to first occurrence of treatment failure.

RESULTS

Mean time to treatment failure was 130 days (95% confidence interval [CI]: 81-n/a) in the ID group versus 114 days (95% CI: 15-155) in the SD group (P=0.36). Similar percentages (ID 30.2%; SD 36.9%) experienced treatment failure. Biopsy-proven acute rejection occurred in 2 (3.2%) ID versus 11 (16.9%) SD patients (P<0.001). Three (2.3%) deaths (2 SD, 1 ID) and five (3.9%) graft losses (3 SD, 2 ID) occurred. Renal function, incidence of infection, and hematologic disorders were comparable in both study cohorts. Gastrointestinal disorders occurred in 51 (81.0%) ID and 49 (75.4%) SD patients with overall similar tolerability as assessed by the Gastrointestinal Symptom Rating Scale.

CONCLUSION

In this exploratory study, the EC-MPS ID regimen reduced the incidence of rejection and showed a comparable safety and tolerability profile to SD. Further examination of this approach in a larger patient cohort is now warranted to confirm these findings.

Toxicity and monitoring of immunosuppressive therapy used in systemic autoimmune diseases

Systemic autoimmune diseases may be progressive and lead to organ system dysfunction and premature death. Current treatment paradigms are usually predominantly based on the administration of immunosuppressive and/or immunomodulatory drug therapy. Such therapy can stabilize systemic manifestations of connective tissue disease (CTD) and may put the disease into remission, and many of these agents are commonly used to treat CTD-associated interstitial lung disease (ILD). Although these agents have largely revolutionized the treatment of the systemic autoimmune diseases, adverse reactions, which can be serious and life threatening, to the various immunosuppressive agents used in the treatment of CTD can occur. Treating physicians must be aware of mechanisms of action of various immunosuppressive agents and be able to recognize the potential adverse reactions that may occur with therapy as well as potentially harmful effects on fetal development. Appropriate monitoring may prevent or limit toxicity from these agents, and knowledge of drug-drug interactions is essential when these agents are prescribed.

Pediatric aspects of therapeutic drug monitoring of mycophenolic acid in renal transplantation

Mycophenolate mofetil (MMF) is widely used for maintenance immunosuppressive therapy in pediatric renal and heart transplant recipients. Children undergo developmental changes (ontogeny) of drug disposition, which may affect drug metabolism of the active compound mycophenolic acid (MPA). Therefore, a detailed characterization of MPA pharmacokinetics and pharmacodynamics in this patient population is required. In general, the overall efficacy and tolerability of MMF in pediatric patients appear to be comparable with those in adults, except for a higher prevalence of gastrointestinal adverse effects in children younger than 6 years. The currently recommended dose in pediatric patients with concomitant cyclosporine is 1200 mg/m(2) per day in 2 divided doses; the recommended MMF dose with concomitant tacrolimus or without a concurrent calcineurin inhibitor is 900 mg/m(2) per day in 2 divided doses. Recent data suggest that fixed MMF dosing results in MPA underexposure (MPA-area under the concentration-time curve (AUC(0-12)), <30 mg × h/L) early posttransplant in approximately 60% of patients. To achieve adequate MPA exposure in most patients, an initial MMF dose of 1800 mg/m(2) per day with concomitant cyclosporine and 1200 mg/m(2) per day with concomitant tacrolimus for the first 2 to 4 weeks posttransplant has been suggested. As in adults, there is an approximately 10-fold variability in dose-normalized MPA-AUC(0-12) values between pediatric patients after renal transplantation, strengthening the argument for concentration-controlled dosing of the drug. Although the clinical utility of therapeutic drug monitoring of MPA for graft outcome and patient survival is still controversial, potential indications are the avoidance of underimmunosuppression, particularly in patients with high immunologic risk in the initial period posttransplant, in patients who are treated with protocols that explore the possibilities of calcineurin inhibitor minimization, withdrawal or even complete avoidance, and steroid withdrawal or avoidance regimens that might also benefit from intensified therapeutic drug monitoring of MPA. An additional indication especially in adolescent patients is the monitoring of drug adherence. Therapeutic drug monitoring of MPA in pediatric solid organ transplantation using limited sampling strategies is preferable over drug dosing based on trough level monitoring only. Several validated pediatric limited sampling strategies are available. Clearly, more research is required to determine whether pediatric patients will benefit from therapeutic drug monitoring of MPA for long-term maintenance immunosuppression with MMF.

SLCO1B1 genetic polymorphism influences mycophenolic acid tolerance in renal transplant recipients

AIMS

This study aimed to determine the influence of gene candidates on mycophenolic acid (MPA) response during the first year of renal transplantation.

MATERIALS & METHODS

A total of 218 renal transplant recipients who received MPA from the first day of transplantation at a fixed dose of 2 g/day were genotyped for ABCB1, ABCC2, UGT2B7, UGT1A9, SLCO1B1, SLCO1B3 and IMPDH1 polymorphisms. Clinical end points were MPA-related adverse drug reactions (ADRs) and acute rejection episodes during the first year post-transplantation.

RESULTS

After correction for multiple statistical testing, SLCO1B1 (encoding the hepatic uptake transporter OATP1B1) was the only gene associated with MPA-related ADRs, showing a 75% risk reduction in favor of a protective effect of the SLCO1B1*5 allele (p = 0.002). In vitro experiments showed that MPA metabolites MPA-phenyl-glucuronide and MPA-acyl-glucuronide are substrates of OATP1B1. Their transport was decreased in the presence of the variant transporter (OATP1B1*5).

CONCLUSION

These results suggest for the first time that carriers of the SLCO1B1*5 allele seem to be protected from MPA-related ADRs.

The evolution of population pharmacokinetic models to describe the enterohepatic recycling of mycophenolic acid in solid organ transplantation and autoimmune disease

With the increasing use of mycophenolic acid (MPA) as an immunosuppressant in solid organ transplantation and in treating autoimmune diseases such as systemic lupus erythematosus, the need for strategies to optimize therapy with this agent has become increasingly apparent. This need is largely based on MPA's significant between-subject and between-occasion (within-subject) pharmacokinetic variability. While there is a strong relationship between MPA exposure and effect, the relationship between drug dose, plasma concentration and exposure (area under the concentration-time curve [AUC]) is very complex and remains to be completely defined. Population pharmacokinetic models using various approaches have been proposed over the past 10 years to further evaluate the pharmacokinetic and pharmacodynamic behaviour of MPA. These models have evolved from simple one-compartment linear iterations to complex multi-compartment versions that try to include various factors, which may influence MPA's pharmacokinetic variability, such as enterohepatic recycling and pharmacogenetic polymorphisms. There have been major advances in the understanding of the roles transport mechanisms, metabolizing and other enzymes, drug-drug interactions and pharmacogenetic polymorphisms play in MPA's pharmacokinetic variability. Given these advances, the usefulness of empirical-based models and the limitations of nonlinear mixed-effects modelling in developing mechanism-based models need to be considered and discussed. If the goal is to individualize MPA dosing, it needs to be determined whether factors which may contribute significantly to variability can be utilized in the population pharmacokinetic models. Some pharmacokinetic models developed to date show promise in being able to describe the impact of physiological processes such as enterohepatic recycling. Most studies have historically been based on retrospective data or poorly designed studies which do not take these factors into consideration. Modelling typically has been undertaken using non-controlled therapeutic drug monitoring data, which do not have the information content to support the development of complex mechanistic models. Only a few recent modelling approaches have moved away from empiricism and have included mechanisms considered important, such as enterohepatic recycling. It is recognized that well thought-out sampling schedules allow for better evaluation of the pharmacokinetic data. It is not possible to undertake complex absorption modelling with very few samples being obtained during the absorption phase (which has often been the case). It is important to utilize robust AUC monitoring which is now being propagated in the latest consensus guideline on MPA therapeutic drug monitoring. This review aims to explore the biological factors that contribute to the clinical pharmacokinetics of MPA and how these have been introduced in the development of population pharmacokinetic models. An overview of the processes involved in the enterohepatic recycling of MPA will be provided. This will summarize the components that complicate absorption and recycling to influence MPA exposure such as biotransformation, transport, bile physiology and gut flora. Already published population pharmacokinetic models will be examined, and the evolution of these models away from empirical approaches to more mechanism-based models will be discussed.

LC-MS/MS for immunosuppressant therapeutic drug monitoring

Due to their narrow therapeutic indices and highly variable pharmacokinetics, therapeutic drug monitoring is necessary to individualize immunosuppressant dosage following organ transplantation. Until recently, monitoring was performed primarily using immunoassays, however, there is an increasing shift to HPLC coupled with MS/MS, due to its greater sensitivity and specificity. Online sample clean-up with either a single analytical column or with 2D chromatography significantly reduces manual handling and is essential to minimize matrix effects and maximize specificity and, coupled with rapid chromatography, allows the simultaneous analysis of the major immunosuppressants, with rapid sample throughput. Thus, LC-MS/MS is an attractive and versatile technique that facilitates rapid development of analytical methods, including new immunosuppressants as they become approved for clinical use.

Pharmacogenetic impact of UDP-glucuronosyltransferase metabolic pathway and multidrug resistance-associated protein 2 transport pathway on mycophenolic acid in thoracic transplant recipients: an exploratory study

STUDY OBJECTIVE

To assess the contribution of polymorphisms in the uridine diphosphate glucuronosyltransferase gene (UGT) and the multidrug resistance-associated protein 2 gene (ABCC2) to mycophenolic acid (MPA) pharmacokinetics and clinical outcomes in thoracic transplant recipients.

DESIGN

Open-label, cross-sectional study.

SETTING

Transplant clinic in Vancouver, British Columbia, Canada.

PATIENTS

Sixty-eight thoracic (36 lung, 32 heart) transplant recipients who were receiving steady-state oral mycophenolate mofetil.

MEASUREMENTS AND MAIN RESULTS

Eleven blood samples were obtained from each patient over a 12-hour dosing period. Plasma concentrations of MPA (active metabolite of mycophenolate mofetil), the MPA metabolites 7-Omycophenolic acid glucuronide (MPAG) and acyl glucuronide (AcMPAG), and free MPA were measured, and dose-normalized conventional pharmacokinetic parameters were determined by noncompartmental methods. Genetic polymorphisms in UGT and ABCC2 were determined by sequencing, and their contributions to pharmacokinetic variability were investigated by using multivariate analysis. For both the lung and heart transplant groups, the UGT2B7 variant 802T (Tyr(268) or UGT2B7*2, rs7439366) and the UGT2B7 variant -138A modified AcMPAG exposure (2.5-3.7-fold and 9.3-12.3-fold higher AcMPAG area under the concentration-time curve [AUC] and AcMPAG:MPA ratio, respectively). In an exploratory analysis, occurrences of rejection, infection, anemia, and leukopenia were associated with an AcMPAG AUC greater than 50 μg·hour/ml and an AcMPAG:MPA ratio greater than 2.

CONCLUSION

UGT2B7 is a promising gene candidate that may influence MPA pharmacokinetics clinically; however, larger clinical pharmacogenetic studies in thoracic transplant subpopulations are warranted to corroborate the role of AcMPAG and UGT2B7 variants in optimizing mycophenolate mofetil therapy.

A limited sampling strategy for estimation of the area under the curve (0 to 8 hours) of mycophenolic acid administered three times daily to liver transplant recipients

OBJECTIVES

Gastrointestinal side-effects caused by mycophenolic acid (MPA) are frequent in liver transplant recipients, and in these cases a switch from two to three daily doses is usually recommended. However, a limited sampling strategy for the estimation of MPA area under the curve from 0 to 8 hours (AUC(0-8h)) has not been made.

DESIGN AND METHODS

In 22 liver transplant patients who were administered MPA three times daily, the trapezoidal extrapolated MPA AUC(0-8h) values using a sampling time from 0 to 2 hours were calculated.

RESULTS

A tentative therapeutic range for MPA AUC(0-8h) of about 20-40 μg.h/mL is proposed, and in the 13 patients with supratherapeutic values the total leukocyte blood count was significantly lower than in the 9 patients with AUC(0-8h) ≤ 40 μg.h/mL (P < 0.001). Significant negative correlations were found between the total leukocyte blood count and the MPA trough levels (r = -0.458; P < 0.05), AUC(0-8h) (r = -0.479; P < 0.05), and AUC(0-2h) (r = -0.437; P < 0.05). A significant correlation was found between the trapezoidal extrapolated AUC(0-8h) and trapezoidal AUC(0-2h) results (r = 0.850; P < 0.001).

CONCLUSIONS

The trapezoidal extrapolated AUC(0-8h), and possibly trapezoidal AUC(0-2h), may be useful for routine therapeutic MPA monitoring in liver transplant recipients in which the dosing frequency is increased from twice to three times a day.

Population pharmacokinetics of mycophenolic acid in children and young people undergoing blood or marrow and solid organ transplantation

AIMS

To characterize the population pharmacokinetics of mycophenolic acid (MPA) and evaluate dose regimens using a simulation approach and accepted therapeutic drug monitoring targets in children and young people undergoing blood or marrow, kidney and liver transplantation.

METHODS

MPA concentration-time data were collected using an age specific sampling protocol over 12h. Some patients provided randomly timed but accurately recorded blood samples. Total and unbound MPA were measured by HPLC. NONMEM was employed to analyze MPA pharmacokinetic data. Simulations (n= 1000) were conducted to assess the suitability of the MPA dose regimens to maintain total MPA AUC(0,12h) within the range 30 and 60mg l(-1) h associated with optimal outcome.

RESULTS

A two-compartment pharmacokinetic model with first-order elimination best described MPA concentration-time data. Population mean estimates of MPA clearance, inter-compartmental clearance, volumes of distribution in the central and peripheral compartments, absorption rate constant and bioavailability were 6.42 l h(-1) , 3.74 l h(-1) , 7.24 l, 16.8l, 0.39h(-1) and 0.48, respectively. Inclusion of bodyweight and concomitant ciclosporin reduced the inter-individual variability in CL from 54.3% to 31.6%. Children with a bodyweight of 10kg receiving standard MPA dose regimens achieve an MPA AUC below the target range suggesting they may be at a greater risk of acute rejection.

CONCLUSIONS

The population pharmacokinetic model for MPA can be used to explore dosing guidelines for safe and effective immunotherapy in children and young people undergoing transplantation.

Pharmacokinetics and pharmacodynamics of mycophenolate sodium (EC-MPS) co-administered with cyclosporine in the early-phase post-kidney transplantation

Mycophenolate drug levels are decreased by co-administration of cyclosporine. However, mycophenolate levels may be associated with insufficient immunosuppression. We investigated the pharmacokinetics of 720 mg mycophenolate sodium (EC-MPS) and inosine monophosphate dehydrogenase (IMPDH) activity under co-medication with cyclosporine and steroids within the first 30 d after kidney transplantation (n = 24). Blood samples were drawn at 0, 0.5, 1, 1.5, 2, 3, 4, 6, 8, and 12 h after the morning dose. Plasma concentrations of mycophenolic acid, its glucuronide metabolites (MPAG; AcMPAG), and free MPA were determined using validated HPLC-DAD. IMPDH activity in leukocytes was analyzed chromatographically. Only six of 24 patients had an MPA-AUC(12h) within the putative therapeutic range of 40-60 mg/L·h. MPA clearance was high with 29 L/h. fMPA-AUC(12h) (r = -0.429, p = 0.04) and MPAG-AUC(12h) correlated significantly with the glomerular filtration rate, while total MPA did not. The MPAG-AUC(12h) was about 52-fold higher than the corresponding values for MPA, whereas the AcMPAG-AUC(12h) reached about 20.4% of the respective MPA-AUC(12h.) We found significant correlations between IMPDH inhibition and MPA concentration (r = -0.665; p < 0.0001), fMPA (r = -0.446; p = 0.003), and AcMPAG (r = -0.459; p = 0.002) but not with MPAG. Only 25% of the patients attained the therapeutic range for MPA-AUC under standard EC-MPS dose during the early-phase post-transplantation. We recommend that EC-MPS should be given in higher doses (3 × 720 mg) in the early post-transplant period when co-administered with cyclosporine.

Development of a Bayesian estimator for the therapeutic drug monitoring of mycophenolate mofetil in children with idiopathic nephrotic syndrome

The use of mycophenolate mofetil (MMF) in children with idiopathic nephrotic syndrome (INS) is increasing. However, the clinical benefit of its monitoring has been scarcely studied, and little is known about its pharmacokinetics in this context. The objectives of the present study were: (i) to study and model the pharmacokinetics of mycophenolic acid (MPA; the active moiety of MMF) in paediatric patients with INS given MMF, at all stages of the disease; (ii) to develop a Bayesian estimator (MAP-BE) for individual inter-dose area under the concentration-time curve (AUC) prediction in this population, using a limited blood sampling strategy (LSS). Full-pharmacokinetic (PK) profiles of MPA collected in paediatric inpatients with INS already treated with a maintenance immunosuppressive therapy based on MMF (with no calcineurin inhibitors; CNI) were studied. A classical iterative two-stage (ITS) method was applied to model the data and develop MAP-BEs using a one-compartment open model where the absorption is described by a double gamma law allowing the description of a potential enterohepatic recirculation. The performance of the MAP-BE developed for individual exposure assessment was evaluated by the bias and precision of predicted AUCs with respect to measured, trapezoidal AUCs (reference value), and by the proportion of predicted AUCs with absolute error >20%. These PK tools were tested in an independent group of patients. Sixty PK profiles of MPA from children receiving MMF in association to corticosteroids or given alone were included in the study. Forty-five of these PK profiles were used to develop a PK model and a MAP-BE, and 15 for their validation. In the building group, the PK model fitted accurately the PK profiles of MPA: mean residual error of modelled vs. reference AUC was m±SD=-0.015±0.092 (range: -0.153 to 0.204). The MAP-BE which allowed the estimation of MPA AUC on the basis of a 20 min-60 min-180 min LSS was then developed. In the independent group of patients, its mean residual error vs. reference AUCs was m±SD=-0.036±0.145 (range: -0.205 to 0.189). Thus, a PK model and its derived MAP-BE for MMF (without any associated CNI) when given to children with INS have been developed. Clinical trials using these PK tools could test the potential impact of the therapeutic drug monitoring of MMF based on the AUC on the clinical evolution of INS.

Biomarkers as a tool for management of immunosuppression in transplant patients

Therapeutic drug monitoring is a well-established approach in transplantation medicine to guide immunosuppressive therapy. However, it cannot always predict the effects of immunosuppressive drugs on immune cells, because it does not reflect any aspect of an individual patient's immune system. Pharmacodynamic monitoring is a more recent strategy to provide information about the biologic effect of a specific drug or drug combination on the individual transplant patient. Currently, there is a large number of different biomarkers that either directly (specific markers) or indirectly (global markers) relate to the pharmacodynamic effects of immunosuppressive drugs and are under investigation as potential candidates to be introduced in clinical practice. Such biomarkers may be useful to identify patients at risk of developing acute rejection, infection, or cancer as well as patients who are suitable for minimization of immunosuppressant therapy and may be helpful to manage the timing and rate of immunosuppressant weaning. Serial longitudinal monitoring may allow maintenance of an individualized immunosuppressive regimen. Thus, biomarker monitoring is a potential complementary tool to therapeutic drug monitoring. This review summarizes the current state of knowledge about the use of a number of global or drug-specific pharmacodynamic biomarkers. It is not a comprehensive overview of the literature available, but rather an evidence-based reflection by experts who are intensively involved in scientific work in this field.

Impact of changing from cyclosporine to tacrolimus on pharmacokinetics of mycophenolic acid in renal transplant recipients with diabetes

The rate of mycophenolic acid (MPA) absorption after oral administration of mycophenolate mofetil (MMF) is delayed in patients with diabetes. Cyclosporine (CsA) decreases MPA exposure by inhibiting enterohepatic recirculation of MPA/MPA glucuronide, and tacrolimus (TRL) may alter the rate and extent of MPA absorption due to its prokinetic properties especially in patients with diabetic gastroparesis. This study evaluated the effect of changing from CsA to TRL on pharmacokinetics of MPA in stable renal transplant recipients with long-standing diabetes. Eight patients were switched from a stable dose of CsA to TRL while taking MMF 1 g twice daily. The 12-hour steady-state total plasma concentration-time profiles of MPA and MPA glucuronide were obtained after oral administration of MMF on 2 occasions: first while taking CsA and second after changing to TRL. Pharmacokinetic parameters of MPA were calculated by the noncompartmental method. Changing from CsA to TRL resulted in significantly increased MPA exposure (area under the concentration-time curve from 0 to 12 hours, AUC0-12) by 46 +/- 32% (P = 0.012) and MPA predose concentration (C0) by 121 +/- 67% (P = 0.008). The magnitude of change in MPA exposure did not correlate well with MPA-C0 or CsA trough concentration. Switching to TRL had minimal impact on peak concentration of MPA (15.0 +/- 6.9 mg/L with CsA versus 16.1 +/- 9.7 mg/L with TRL, P = 0.773) and time to reach the peak concentration (1.0 +/- 0.4 hours with CsA versus 1.2 +/- 0.8 hours with TRL, P = 0.461). Highly variable and unpredictable changes in MPA exposure among renal transplant patients with diabetes do not support a strategy of preemptively adjusting MMF dose when switching calcineurin inhibitors in this population.

UPLC MS/MS method for quantification of mycophenolic acid and metabolites in human plasma: Application to pharmacokinetic study

BACKGROUND

We described the development and full validation of a rapid, high throughput sensible and accurate UPLC method using tandem mass spectrometry detection for mycophenolate acid (MPA) and its metabolites, MPA glucuronide (MPAG) and acyl MPA glucuronide (AcMPAG) concentration determination with MPA-D3 as internal standard in human plasma.

METHODS

Plasma pretreatment involved a one-step protein precipitation with acetonitrile. The separation was performed by reverse-phase chromatography on a Waters BEH HSST3 100 mm*2.1 mm*1.8 μm column. The multiple reaction monitoring transitions used for quantification were m/z 321.04→303.02 for MPA, 524.09→303.02 for AcMPAG and MPAG and 324.03→306.04 for MPA-D3 in the electrospray positive ionization mode.

RESULTS

The method was linear over the concentration range of 0.1-20mg/L for MPA and AcMPAG and 1-200mg/L for MPAG respectively. The intra- and inter-day precision values were below 14% and accuracy was from 94.0 to 103.3% at all quality control levels. The lower LOQ was 0.1 mg/L for MPA and AcMPAG, 1 mg/L for MPAG.

CONCLUSION

Sample analysis time was reduced to 7 min including sample preparation. The present method was successfully applied to a pharmacokinetic study following oral administration of enterocoated sodium mycophenolate in de novo renal transplantation.

Target enzyme activity as a biomarker for immunosuppression

Pharmacokinetic drug monitoring has been used for many years to relate immunosuppressant dose to drug exposure in vivo. However, this conventional therapeutic drug monitoring of blood immunosuppressant levels may not necessarily predict the pharmacologic effects on immune cells. The direct determination of target enzyme activity (eg, calcineurin activity, inosine-5'-monophospahte dehydrogenase [IMPDH] activity, p70S6 kinase) may help to better assess the individual response to the immunosuppressant. However, its use is limited by the difficulties of the assay systems, which did not allow yet the prospective assessment of these enzymes in larger patient cohorts with the establishment of validated pharmacodynamic drug monitoring. The most progress regarding a robust and reproducible test system has been achieved with the determination of IMPDH activity as a specific pharmacodynamic parameter of mycophenolic acid activity. This recently validated and standardized assay allows the investigation of IMPDH activity in larger clinical studies. Although the determination of target enzyme activity, eg, by the determination of IMPDH activity, holds promise for a more individualized therapy in transplant medicine, more studies are needed to prospectively validate this approach.

Pharmacokinetic and pharmacodynamic analysis of enteric-coated mycophenolate sodium: limited sampling strategies and clinical outcome in renal transplant patients

AIMS

Pharmacokinetic (PK) and pharmacodynamic (PD) monitoring strategies and clinical outcome were evaluated in enteric-coated mycophenolate sodium (EC-MPS)-treated renal allograft recipients.

METHODS

PK [mycophenolic acid (MPA)] and PD [inosine monophosphate dehydrogenase (IMPDH) activity] data were analysed in 66 EC-MPS and ciclosporin A (CsA)-treated renal allograft recipients. Adverse events were considered in a follow-up period of 12 weeks.

RESULTS

Analyses confirmed a limited sampling strategy (LSS) consisting of PK and PD data at predose, 1, 2, 3 and 4 h after oral intake as an appropriate sampling method (MPA r(2)= 0.812; IMPDH r(2)= 0.833). MPA AUC(0-12) of patients with early biopsy-proven acute rejection was significantly lower compared with patients without a rejection (median MPA AUC(0-12) 28 microg*h ml(-1) (7-45) vs. 40 microg*h ml(-1) (16-130), P < 0.01), MPA AUC(0-12) of patients with recurrent infections was significantly higher compared with patients without infections (median MPA AUC(0-12) 65 microg*h ml(-1) (range 37-130) vs. 37 microg*h ml(-1) (range 7-120), P < 0.005). Low 12-h IMPDH enzyme activity curve (AEC(0-12)) was associated with an increased frequency of gastrointestinal side-effects (median IMPDH AEC(0-12) 43 nmol*h mg(-1) protein h(-1)[range 12-67) vs. 75 nmol*h mg(-1) protein h(-1) (range 15-371), P < 0.01].

CONCLUSIONS

Despite highly variable absorption data, an appropriate LSS might be estimated by MPA AUC(0-4) and IMPDH AEC(0-4) in renal transplant patients treated with EC-MPS and CsA. Regarding adverse events, the suggested MPA-target AUC(0-12) from 30 to 60 microg*h ml(-1) seems to be appropriate in renal allograft recipients.

Population pharmacokinetics and Bayesian estimator of mycophenolic acid in children with idiopathic nephrotic syndrome

AIMS

To develop a population pharmacokinetic model for mycophenolic acid (MPA) in children with idiopathic nephrotic syndrome (INS) treated with mycophenolate mofetil (MMF), identify covariates that explain variability and determine the Bayesian estimator of the area under the concentration-time curve over 12 h (AUC(0-12)).

METHODS

The pharmacokinetic model of MMF was described from 23 patients aged 7.4 +/- 3.9 years (range 2.9-14.9) using nonlinear mixed-effects modelling (NONMEM) software. A two-compartment model with lag-time and first-order absorption and elimination was developed. The final model was validated using visual predictive check. Bayesian estimator was validated using circular permutation method.

RESULTS

The population pharmacokinetic parameters were apparent oral clearance 9.7 l h(-1), apparent central volume of distribution 22.3 l, apparent peripheral volume of distribution 250 l, inter-compartment clearance 18.8 l h(-1), absorption rate constant 5.16 h(-1), lag time 0.215 h. The covariate analysis identified body weight and serum albumin as individual factors influencing the apparent oral clearance. Accurate Bayesian estimation of AUC(0-12) was obtained using the combination of three MPA concentrations measured just before (T(0)), 1 and 4 h (T(1) and T(4)) after drug intake with a small error of 0.298 microg h(-1) ml(-1) between estimated and reference AUC(0-12).

CONCLUSIONS

The population pharmacokinetic model of MPA was developed in children with INS. A three-point (T(0), T(1) and T(4)h) Bayesian estimator of AUC(0-12) was developed and might be used to investigate the relation between MPA pharmacokinetic and pharmacodynamics in children with INS and determine if there is any indication to monitor MPA exposure in order to improve patient outcome based on individual AUC-controlled MMF dosing.

Cost-effectiveness analysis of individualized mycophenolate mofetil dosing in kidney transplant patients in the APOMYGRE trial

BACKGROUND

In the prospective, randomized, multicenter APOMYGRE trial conducted in France, concentration-controlled mycophenolate mofetil (MMF) dosing based on mycophenolic acid (MPA) exposure significantly reduced the treatment failure and acute rejection during the first posttransplantation year compared with fixed-dose MMF. This analysis investigated the cost effectiveness of dose individualization.

METHOD

The study included 65 patients per group (intent-to-treat population). Treatment failure (primary efficacy endpoint) was defined as death, graft loss, acute rejection, or MMF discontinuation because of adverse effects. Data on hospitalizations, drugs prescribed, physicians' fees, laboratory expenses, ambulatory visits, and transportation were retrieved. Costs were calculated from the French National Health System perspective.

RESULTS

The mean (95% confidence interval) total yearly cost per patient was Euro 47,477 (Euro 43,933; Euro 51,020) in the concentration-controlled group and Euro 46,783 ( Euro 44,152; Euro 49,414) in the fixed-dose group (P=0.7). The observed incremental cost-effectiveness ratio was Euro 3757 per treatment failure (Purchasing Power Parities United States/France: $4129). Hospitalization and drug costs accounted for approximately 50% and 25% of total costs, respectively. The cost for MPA area under the concentration-time curve and dose calculation was Euro 452 per patient, less than 1% of the total cost.

CONCLUSION

In the APOMYGRE trial, therapeutic MPA monitoring using a limited sampling strategy reduced the risk of treatment failure and acute rejection in renal allograft recipients during the first 12 months posttransplantation, at neutral cost.

Mycophenolate pharmacokinetics and association with response to acute graft-versus-host disease treatment from the Blood and Marrow Transplant Clinical Trials Network

There are limited data as to the effectiveness of mycophenolate mofetil (MMF) plus high-dose corticosteroids for the treatment of acute graft-versus-host disease (aGVHD), and even less data regarding the pharmacokinetic disposition and exposure-response relationship of MMF in individuals with GVHD. MMF pharmacokinetics were studied in a multicenter Blood and Marrow Transplant Clinical Trials Network randomized phase II trial evaluating the effectiveness of MMF as one of 4 agents added to corticosteroids as treatment of aGVHD. Thirty-two of the patients randomized to receive MMF underwent pharmacokinetic sampling in weeks 1 and 2 were studied. Mean age was 41 +/- 13.6 years. Twenty one (65.6%), 5 (15.6%), 6 (18.8%) patients had a complete response (CR), partial response (PR) or lesser response by day 28, respectively. Twenty-five (78.1%), 2 (6.3%), 5 (15.6%) patients had a CR, PR, or other response by day 56 to treatment, respectively. Mycophenolic acid (MPA) pharmacokinetic measurements from weeks 1 and 2 did not correlate with CR at either day 28 or day 56 (P > .07); however, if the mean of weeks 1 and 2 total MPA troughs was >0.5 microg/mL or that of an unbound trough was >0.015 microg/mL, then a significantly greater proportion achieved CR + PR at days 28 and 56. CR + PR at day 28 was observed in 19 of 19 patients (100%) with a mean total trough >0.5 mg/mL, but in only 7 of 13 (54%) with a mean total trough < or =0.5 microg/mL (P = .002). Similarly, CR + PR at day 28 was seen in 15 of 15 patients (100%) with an unbound trough concentration >0.015 microg/mL, but in only 11 of 17 (65%) with an unbound trough concentration < or =0.015 microg/mL (P = .02). There was no association between the pharmacokinetic measures and risk of infection by day 90 or overall survival (OS) at day 180 postrandomization. About one-half of subjects did not achieve the favorable MPA total and unbound trough concentrations. The current practice of MMF 1 gm twice daily dosing provides low plasma concentrations in many patients. Higher doses may improve the efficacy of MMF as aGVHD therapy.

Inosine monophosphate dehydrogenase variability in renal transplant patients on long-term mycophenolate mofetil therapy

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

* Mycophenolic acid (MPA) is a potent, selective and reversible inhibitor of inosine 5'-monophosphate dehydrogenase (IMPDH), the rate-limiting enzyme for de novo guanosine triphosphate biosynthesis. * The large IMPDH interindividual variability could be responsible for the differences in therapeutic effects and side-effects observed with MPA. * Induction of IMPDH activity has been observed in whole blood during immunosuppressive therapy.

WHAT THIS STUDY ADDS

* Our data were acquired in long-term mycophenolate mofetil-treated renal transplant recipients on different combinations of immunosuppressive agents (ciclosporin, tacrolimus, sirolimus) and with different treatment duration (up to 8.8 years post transplant). * The increasing trend in IMPDH activity that we observed throughout our 12-month observation period was significantly higher in rejecting than in nonrejecting subjects.

AIMS

Long-term mycophenolate mofetil (MMF) therapy may induce inosine 5'-monophosphate dehydrogenase (IMPDH) activity in peripheral blood mononuclear cells (PBMCs), thus decreasing MMF immunosuppressive properties. Pharmacodynamic monitoring was used to investigate whether biological activity is altered after long-term therapy.

METHODS

IMPDH activity was measured in PBMC samples from 54 stable kidney transplant patients, already on MMF (for at least 3 months), before (t(0)) and 2 h after (t(2)) MMF morning dose administration; levels were monitored for up to 15 months, together with total mycophenolic acid (MPA) and free MPA concentrations.

RESULTS

During the 15 months' monitoring, t(0) IMPDH activity in transplant recipients increased from 5.9 +/- 3.7 nmol h(-1) mg(-1)[95% confidence interval (CI) 4.9, 6.9] to 9.0 +/- 3.9 nmol h(-1) mg(-1) (95% CI 7.2, 10.8), with an intra- and interpatient variability of 28% and 42%. Five patients experienced acute rejection during the follow-up: t(0) IMPDH activity was increased during rejection vs. nonrejection, and the trend was significantly higher in rejecting than in nonrejecting subjects for the whole monitoring period.

CONCLUSIONS

Even though a correlation has been found between IMPDH activity and rejection, its efficacy as a predictive tool in long-term transplant outcomes may be affected by high interpatient variability; on the other hand, continuous monitoring of the IMPDH trend could make an effective prognostic parameter of rejection. Other trials also including pre-transplant data on both IMPDH expression and activity are warranted to better assess their role as biomarkers for MPA effect in clinical practice.

Pharmacokinetic optimization of immunosuppressive therapy in thoracic transplantation: part II

Part I of this article, which appeared in the previous issue of the Journal, reviewed calcineurin inhibitors--ciclosporin and tacrolimus. In part II, we review the pharmacokinetics and therapeutic drug monitoring of mycophenolate and mammalian target of rapamycin inhibitors--sirolimus and everolimus--in thoracic transplantation, and we provide an overall discussion and suggest various areas for future study.

Mycophenolic acid exposure after administration of mycophenolate mofetil in the presence and absence of cyclosporin in renal transplant recipients

BACKGROUND AND OBJECTIVE

The pharmacokinetics of mycophenolic acid (MPA) are complex, with large interindividual variability over time. There are also well documented interactions with cyclosporin, and assessment of MPA exposure is therefore necessary when reducing or stopping cyclosporin therapy. Here we report on the pharmacokinetic and pharmacodynamic behaviour of MPA in renal transplant patients on standard dose, reduced dose and no cyclosporin.

STUDY DESIGN

The CAESAR study, a prospective 12-month study in primary renal allograft recipients, was designed to determine whether mycophenolate mofetil-based regimens containing either low-dose cyclosporin or low-dose cyclosporin withdrawn by 6 months could minimize nephrotoxicity and improve renal function without an increase in acute rejection compared with a mycophenolate mofetil-based regimen containing standard-dose cyclosporin.

PATIENTS AND METHODS

A subset of patients from the CAESAR study contributed to this pharmacokinetic analysis of MPA exposure. Blood samples were taken over one dosing interval on day 7 and at months 3, 7 and 12 post-transplantation. The sampling time points were predose, 20, 40 and 75 minutes and 2, 3, 4, 6, 8 and 12 hours after mycophenolate mofetil dosing. Assessments included plasma concentrations of MPA and mycophenolic acid glucuronide (MPAG) and cyclosporin trough concentrations. The area under the plasma concentration-time curve (AUC) from 0 to 12 hours (AUC(12)) for MPA was the primary pharmacokinetic parameter, and the AUC(12) for MPAG was the secondary parameter.

RESULTS

In total, 536 de novo renal allograft recipients were randomized in the CAESAR study. Of these, 114 patients were entered into the pharmacokinetic substudy and 110 patients contributed to the pharmacokinetic analysis. There was a rapid rise in MPA concentrations (median time to peak concentration 0.72-1.25 hours). At day 7 and month 3, the MPA AUC(12) values were similar in the cyclosporin withdrawal and low-dose cyclosporin groups (patients with the same cyclosporin target concentrations to month 6), while at 7 and 12 months, the values in the cyclosporin withdrawal group were higher than in the low-dose group (19.9% and 30.2% higher, respectively). MPA AUC(12) values in the standard-dose cyclosporin group were lower than in the other groups at all time points and increased over time. At all time points, the MPA peak plasma concentration was similar in all groups, and the MPAG concentrations rose more slowly than MPA concentrations. The ratio of the AUC from 6 to 12 hours/AUC(12) suggests that an increasing AUC in the cyclosporin withdrawal group is due to an increase in the enterohepatic recirculation.

CONCLUSION

These findings are consistent with the hypothesis that cyclosporin inhibits the biliary secretion and/or hepatic extraction of MPAG, leading to a reduced rate of enterohepatic recirculation of MPA. Several concurrent mechanisms, such as cyclosporin-induced changes in renal tubular MPAG excretion and enhanced elimination of free MPA through competitive albumin binding with MPAG, can also contribute to the altered MPAG pharmacokinetics observed in the presence and absence of cyclosporin.

A therapeutic exploratory study to determine the efficacy and safety of calcineurin-inhibitor-free de-novo immunosuppression after liver transplantation: CILT

Background

Immunosuppression with calcineurin inhibitors (CNI) increases the risk of renal dysfunction after orthotopic liver transplantation (OLT). Controlled trials have shown improvement of renal function in patients that received delayed and/or reduced-dose CNI after OLT. Delaying immunosuppression with CNI in combination with induction therapy does not increase the risk of acute rejection but reduces the incidence of acute renal dysfunction. Based on this clinical data this study protocol was designed to assess the efficacy and safety of calcineurin-inhibitor-free de-novo immunosuppression after liver transplantation.

Methods/Design

A prospective therapeutic exploratory, non-placebo controlled, two stage monocenter trial in a total of 29 liver transplant patients was designed to assess the safety and efficacy of de-novo CNI-free immunosuppression with basiliximab, mycophenolate sodium, prednisolone and everolimus. The primary endpoint is the rate of steroid resistant rejections. Secondary endpoints are the incidence of acute rejection, kidney function (assessed by incidence and duration of renal replacement therapy, incidence of chronic renal failure, and measurement glomerular filtration rate), liver allograft function (assessed by measurement of AST, ALT, total bilirubin, AP, GGT), treatment failure, (i. e., re-introduction of CNI), incidence of adverse events, and mortality up to one year after OLT.

Discussion

This prospective, two-stage, single-group pilot study represents an intermediate element of the research chain. If the data of the phase II study corroborates safety of de-novo CNI-free immunosuppressive regimen this should be confirmed in a randomized, prospective, controlled double-blinded clinical trial. The exploratory data from this trial may then also facilitate the design (e. g. sample size calculation) of this phase III trial.

Trial registration number

NCT00890253 (clinicaltrials.gov)

Renal transplant patients at high risk of acute rejection benefit from adequate exposure to mycophenolic acid

BACKGROUND

To better define subpopulations in which achieving adequate mycophenolic acid (MPA) concentrations quickly would be important, a post hoc exploratory analysis on the fixed-dose concentration-controlled database was performed, comparing high- versus low-risk renal transplant patients.

METHODS

Renal transplant patients were treated with mycophenolate mofetil, corticosteroids, and cyclosporine A or tacrolimus. Patients were defined as "high risk" if they had one or more of the following characteristics: delayed graft function, second or third transplantation, panel reactive antibodies >15%, four or more human leukocyte antigen mismatches, or were of black race.

RESULTS

A total of 549 patients (61%) were classified as high risk, of whom 284 were on cyclosporine A treatment and 265 on tacrolimus. In high-risk patients, the difference in rejection incidence was 14.3% in the MPA-area under the concentration (AUC) less than 30 mg hr/L vs. 7.8% in the MPA-AUC more than or equal to 30 mg hr/L groups (P=0.025) during the first month after transplantation; whereas, in low-risk patients, there were similar rejection rates (5.7% vs. 4.5%). In the subgroup of high-risk tacrolimus-treated patients, the difference in acute rejection incidence in the first month between patients with MPA-AUC0-12 less than or more than or equal to 30 mg hr/L was most pronounced: 16 of 67 patients (23.9%) vs. 18 of 173 patients (10.4%); P=0.012.

CONCLUSIONS

The incidence of acute rejection is higher in high-risk patients if MPA-AUC0-12 is below 30 mg hr/L. In contrast, a difference in acute rejection incidence in low-risk patients with MPA-AUC0-12 less than or more than or equal to 30 mg hr/L was not observed. This supports the use of a higher mycophenolate mofetil starting dose in selected patient populations early after transplantation.