The impact of routine mycophenolate mofetil drug monitoring on the treatment of cardiac allograft rejection

Therapeutic drug monitoring of mycophenolic acid and azole antifungals on two distinct LC-MS/MS instruments

Background

As an active metabolite of a commonly prescribed immunosuppressant, mycophenolic acid (MPA) levels are often monitored to prevent organ rejection following a transplant. Triazoles are often prescribed for treatment of invasive fungal infections in immunocompromised patients. Due to the variability in individual pharmacokinetics and drug-drug interactions, therapeutic drug monitoring is recommended for triazole antifungals. A multiplex LC-MS/MS assay has been developed that can quantify both MPA and triazole drugs in serum.

Methods

A sample preparation procedure was established to spike in internal standard compounds and precipitate proteins. Reversed-phase chromatographic separation was performed on a C18 column with an analysis time of five minutes per sample. The mass spectrometer was operated in multiple reaction monitoring mode. The method was validated on two HPLC systems interfaced with either a Triple Quad 6500 or an API 4000 instrument.

Results

The multiplex assay was linear over a wide dynamic range with analyte measurable ranges of 0.4-48 μg/mL for MPA, 0.1-12 μg/mL for posaconazole, and 0.2-24 μg/mL for voriconazole, itraconazole, hydroxyitraconazole, and isavuconazole. The between-day and intraday imprecisions were less than 10 %. Limits of detection were below 0.04 ug/mL with limits of quantitation below 0.2 μg/mL. Method comparison studies against the current in-house method met acceptance criteria. The instrument comparison study demonstrated a strong correlation between data collected from the two systems.

Conclusion

A robust multiplex LC-MS/MS assay was developed and validated for monitoring MPA and triazoles drug levels in a clinical laboratory. The assay performance on two distinct instruments was acceptable and comparable.

Influence of UDP-Glucuronosyltransferase Polymorphisms on Mycophenolic Acid Metabolism in Renal Transplant Patients

This study aimed to evaluate the effects of UDP-glucuronosyltransferase (UGT) polymorphisms on mycophenolic acid (MPA) metabolism in renal transplant patients. A total of 11 single nucleotide polymorphisms (SNPs) of UGT1A1, UGT1A7, UGT1A8, UGT1A9, UGT1A10, and UGT2B7 were genotyped in 79 renal transplant patients. The associations of SNPs and clinical factors with dose-adjusted MPA area under the plasma concentration-time curve (AUC/D), the dose-adjusted plasma concentration (C0/D) of 7-O-MPA-glucuronide (MPAG), and the dose-adjusted plasma concentration (C0/D) of acyl MPAG (AcMPAG) were analyzed. In the univariate analysis, UGT1A1 rs4148323, age, and anion gap were associated with MPA AUC/D. MPA AUC/D was higher in patients with the GA genotype of UGT1A1 rs4148323 compared to patients with the GG genotype. UGT1A1 rs4148323, UGT1A9 rs2741049 and clinical factors, including age, serum total bilirubin, adenosine deaminase, anion gap, urea, and creatinine, were associated with MPAG C0/D. UGT2B7 rs7438135, UGT2B7 rs7439366, and UGT2B7 rs7662029 also were associated with AcMPAG C0/D. Multiple linear regression analysis showed that UGT1A9 rs2741049 and indirect bilirubin were negatively correlated with MPAG C0/D (P = .001; P = .039), and UGT2B7 rs7662029 was positively correlated with AcMPAG C0/D (P = .008). This study demonstrates a significant influence of UGT1A9 rs2741049 and UGT2B7 rs7662029 polymorphisms on the metabolism of MPA in vivo.

Therapeutic Drug Monitoring of Mycophenolic Acid as a Precision Medicine Tool for Heart Transplant Patients: Results of an Observational Pharmacokinetic Pilot Study

In the clinical practice management of heart transplant (HTx), the impact of calcineurin inhibitors co-administration on pharmacokinetics (PKs) of mycophenolic acid (MPA), mycophenolate mofetil (MMF) active drug, is not adequately considered. This retrospective study investigated full MPA-PK profiles by therapeutic drug monitoring (TDM) in 21 HTx recipients treated with MMF combined with cyclosporine (CsA) or tacrolimus (TAC) at a median time of 2.6 months post-transplant. The two treatment groups were compared. We described the main MPA-PK parameters in patients developing acute cellular rejection (ACR) and those who did not. Median dose-adjusted MPA-trough levels and MPA-AUC_0-12h were higher in patients co-treated with TAC than with CsA (p = 0.0001 and p = 0.006, respectively). MPA-C_max and T_max were similar between the two groups, whereas the enterohepatic recirculation biomarker of MPA (MPA-AUC_4-12h) was higher in the MMF and TAC group (p = 0.004). Consistently, MPA clearance was higher in the MMF and CsA group (p = 0.006). In total, 87.5% of ACR patients were treated with MMF and CsA, presenting a lower MPA-AUC_0-12h (p = 0.02). This real-world study suggested the CsA interference on MPA-PK in HTx, evidencing the pivotal role of MPA TDM as a precision medicine tool in the early phase after HTx. A prospective study is mandatory to investigate this approach to HTx clinical outcomes.

Association of ABCC2 Haplotypes to Mycophenolic Acid Pharmacokinetics in Stable Kidney Transplant Recipients

Mycophenolic acid exhibits significant interpatient pharmacokinetic variability attributed to factors including race, sex, concurrent medications, and enterohepatic circulation of the mycophenolic acid glucuronide metabolite to mycophenolic acid. This conversion by enterohepatic circulation is mediated by the multidrug resistance-associated protein 2, encoded by ABCC2. This study investigated ABCC2 haplotype associations with mycophenolic acid pharmacokinetics in 147 stable kidney transplant recipients receiving mycophenolic acid in combination with calcineurin inhibitors. The role of the ABCC2 genotypes -24C>T (rs717620), 1249C>T (rs2273697), and 3972C>T (rs3740066) were evaluated in prospective, cross-sectional pharmacokinetic studies of stable recipients receiving mycophenolic acid and either tacrolimus or cyclosporine. Haplotype phenotypic associations with mycophenolic acid pharmacokinetic parameters were computed using THESIAS (v. 3.1). Four ABCC2 haplotypes with estimated frequencies greater than 10% were identified (H1:CGC [wild type], H9:CGT, H2:CAC, H12:TGT). There were no differences in haplotype frequencies by either race or sex. There were significant associations of pharmacokinetic parameters with ABCC2 haplotypes for mycophenolic acid clearance (L/h), mycophenolic acid AUC0-12h (mg·h/L), and the ratio of mycophenolic acid glucuronide to mycophenolic acid AUC0-12h . The wild-type haplotype ABCC2 CGC had greater mycophenolic acid AUC0-12h (P = .017), slower clearance (P = .013), and lower mycophenolic acid glucuronide to mycophenolic acid AUC0-12h ratio (P = .047) compared with the reduced function ABCC2 haplotype CGT. These differences were most pronounced among patients receiving tacrolimus cotreatment. No phenotypic associations were found with the cyclosporine-mycophenolic acid regimen. Variation in ABCC2 haplotypes contributes to subtherapeutic mycophenolic acid exposure and influences interpatient variability in pharmacokinetic phenotypes based on concurrent calcineurin inhibitor treatment.

Personalized Therapy for Mycophenolate: Consensus Report by the International Association of Therapeutic Drug Monitoring and Clinical Toxicology

ABSTRACT

When mycophenolic acid (MPA) was originally marketed for immunosuppressive therapy, fixed doses were recommended by the manufacturer. Awareness of the potential for a more personalized dosing has led to development of methods to estimate MPA area under the curve based on the measurement of drug concentrations in only a few samples. This approach is feasible in the clinical routine and has proven successful in terms of correlation with outcome. However, the search for superior correlates has continued, and numerous studies in search of biomarkers that could better predict the perfect dosage for the individual patient have been published. As it was considered timely for an updated and comprehensive presentation of consensus on the status for personalized treatment with MPA, this report was prepared following an initiative from members of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology (IATDMCT). Topics included are the criteria for analytics, methods to estimate exposure including pharmacometrics, the potential influence of pharmacogenetics, development of biomarkers, and the practical aspects of implementation of target concentration intervention. For selected topics with sufficient evidence, such as the application of limited sampling strategies for MPA area under the curve, graded recommendations on target ranges are presented. To provide a comprehensive review, this report also includes updates on the status of potential biomarkers including those which may be promising but with a low level of evidence. In view of the fact that there are very few new immunosuppressive drugs under development for the transplant field, it is likely that MPA will continue to be prescribed on a large scale in the upcoming years. Discontinuation of therapy due to adverse effects is relatively common, increasing the risk for late rejections, which may contribute to graft loss. Therefore, the continued search for innovative methods to better personalize MPA dosage is warranted.

Effect of the proton-pump Inhibitor pantoprazole on MycoPhenolic ACid exposure in kidney and liver transplant recipienTs (IMPACT study): a randomized trial

BACKGROUND

Mycophenolic acid (MPA) is widely utilized as an immunosuppressant in kidney and liver transplantation, with reports suggesting an independent relationship between MPA concentrations and adverse allograft outcome. Proton-pump inhibitors (PPIs) may have variable effects on the absorption of different MPA formulations leading to differences in MPA exposure.

METHODS

A multicentre, randomized, prospective, double-blind placebo-controlled cross-over study was conducted to determine the effect of the PPI pantoprazole on the MPA and its metabolite MPA-glucuronide (MPA-G) area under the curve (AUC) >12 h (MPA-AUC12 h) in recipients maintained on mycophenolate mofetil (MMF) or enteric-coated mycophenolate sodium (EC-MPS). We planned a priori to examine separately recipients maintained on MMF and EC-MPS for each pharmacokinetic parameter. The trial (and protocol) was registered with the Australian New Zealand Clinical Trials Registry on 24 March 2011, with the registration number of ACTRN12611000316909 ('IMPACT' study).

RESULTS

Of the 45 recipients screened, 40 (19 MMF and 21 EC-MPS) were randomized. The mean (standard deviation) recipient age was 58 (11) years with a median (interquartile range) time post-transplant of 43 (20-132) months. For recipients on MMF, there was a significant reduction in the MPA-AUC12 h [geometric mean (95% confidence interval) placebo: 53.9 (44.0-65.9) mg*h/L versus pantoprazole: 43.8 (35.6-53.4) mg*h/L; P = 0.004] when pantoprazole was co-administered compared with placebo. In contrast, co-administration with pantoprazole significantly increased MPA-AUC12 h [placebo: 36.1 (26.5-49.2) mg*h/L versus pantoprazole: 45.9 (35.5-59.3) mg*h/L; P = 0.023] in those receiving EC-MPS. Pantoprazole had no effect on the pharmacokinetic profiles of MPA-G for either group.

CONCLUSIONS

The co-administration of pantoprazole substantially reduced the bioavailability of MPA in patients maintained on MMF and had the opposite effect in patients maintained on EC-MPS, and therefore, clinicians should be cognizant of this drug interaction when prescribing the different MPA formulations.

Clinical Pharmacokinetic and Pharmacodynamic Monitoring for Mycophenolate Mofetil

The use of mycophenolate mofetil (MMF), in combination with cyclosporine (CsA) or tacrolimus (FK) and corticosteroids, has been shown to improve clinical outcomes through significant reduction in the incidence of acute rejection in solid organ transplant patients. A fixed oral dosing regimen of 1 or 1.5 g MMF twice daily received Food and Drug Administration approval in 1995 with no recommendations for concentration monitoring at that time. Subsequent evidence has generated substantial debate on the need of clinical monitoring for MMF. This article summarizes the rationale, evidence, and approaches of clinical monitoring for MMF. Mycophenolic acid (MPA), the active moiety of MMF, noncompetitively inhibits the enzyme inosine monophosphate dehydrogenase (IMPDH), which is the target enzyme for MPA. Pharmacokinetic monitoring, by use of MPA predose or MPA area under the concentration-time curve (AUC) values, and pharmacodynamic monitoring by analysis of inhibition of IMPDH have been evaluated in organ transplant patients. The possibility of drug interactions between other immunosuppressive agents has also received attention recently. The clinical implications of drug interactions are discussed in this article.

New Antiproliferative Immunosuppressive Agents

Since the early 1980s, the combination of cyclosporine, azathioprine, and prednisone has been the mainstay tripledrug immunosuppressive regimen used in transplantation. However, advances in drug research, design, and development have allowed for the introduction of new agents that have greatly increased the number of immunosuppressive agents available for use in transplant recipients. Particularly, the newer antiproliferative immunosuppressive drugs (agents that directly inhibit the proliferation of T and B lymphocytes) have had an important impact on patient outcomes posttransplant. These agents are mycophenolate mofetil and sirolimus.

The effect of MMF dose and trough levels on adverse effects in pediatric heart transplant recipients

Limited pharmacokinetic and safety data exist for MMF in pediatric HTR. Previously targeted MPA-TL are 1.5-3.0 μg/mL. The objective of this study was to assess the outcomes targeting MPA-TL of 0.8-2.0 μg/mL in pediatric HTR. MPA-TL were retrospectively collected 2-12 months post-transplant. Acute rejection, infection, leukopenia, and GI complaints were then correlated with MPA-TL. A total of 355 MPA-TL from 22 HTR were included. Median age was 2.5 yr. Primary indication for transplant was dilated cardiomyopathy (64%). Mean MPA-TL was 1.7 ± 0.9 μg/mL. African American patients received significantly higher doses (702 ± 235 mg/m(2) ) compared with other races (p = 0.035). Leukopenia was less common in patients with SUB MPA vs. others (p = 0.01). MMF was discontinued for GI complaints in one patient and leukopenia in two patients. One SUB patient had acute rejection, and one SUP patient had infection. One-yr survival was 100%. Targeting a lower range for MPA-TL was not associated with significant rejection or infection. Despite lower MPA-TL, MMF was discontinued in 3/22 patients for adverse effects.

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).

Mycophenolate monitoring in liver, thoracic, pancreas, and small bowel transplantation: a consensus report

Assessing the value of mycophenolic acid (MPA) monitoring outside renal transplantation is hindered by the absence of any trial comparing fixed-dose and concentration-controlled therapy. However, in liver and thoracic transplantation particularly, clinical trials, observational studies with comparison groups, and case series have described MPA efficacy, exposure/efficacy relationships, pharmacokinetic variability, and clinical outcomes relating to plasma MPA concentrations. On the basis of this evidence, this report identifies MPA as an immunosuppressant for which the combination of variable disposition, efficacy, and adverse effects contributes to interindividual differences seemingly in excess of those optimal for a fixed-dosage mycophenolate regimen. Combined with experiences of MPA monitoring in other transplant indications, the data have been rationalized to define circumstances in which measurement of MPA concentrations can contribute to improved management of mycophenolate therapy in nonrenal transplant recipients.

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.

Pharmacokinetic optimization of immunosuppressive therapy in thoracic transplantation: part I

Although immunosuppressive treatments and therapeutic drug monitoring (TDM) have significantly contributed to the increased success of thoracic transplantation, there is currently no consensus on the best immunosuppressive strategies. Maintenance therapy typically consists of a triple-drug regimen including corticosteroids, a calcineurin inhibitor (ciclosporin or tacrolimus) and either a purine synthesis antagonist (mycophenolate mofetil or azathioprine) or a mammalian target of rapamycin inhibitor (sirolimus or everolimus). The incidence of acute and chronic rejection and of mortality after thoracic transplantation is still high compared with other types of solid organ transplantation. The high allogenicity and immunogenicity of the lungs justify the use of higher doses of immunosuppressants, putting lung transplant recipients at a higher risk of drug-induced toxicities. All immunosuppressants are characterized by large intra- and interindividual variability of their pharmacokinetics and by a narrow therapeutic index. It is essential to know their pharmacokinetic properties and to use them for treatment individualization through TDM in order to improve the treatment outcome. Unlike the kidneys and the liver, the heart and the lungs are not directly involved in drug metabolism and elimination, which may be the cause of pharmacokinetic differences between patients from all of these transplant groups. TDM is mandatory for most immunosuppressants and has become an integral part of immunosuppressive drug therapy. It is usually based on trough concentration (C(0)) monitoring, but other TDM tools include the area under the concentration-time curve (AUC) over the (12-hour) dosage interval or the AUC over the first 4 hours post-dose, as well as other single concentration-time points such as the concentration at 2 hours. Given the peculiarities of thoracic transplantation, a review of the pharmacokinetics and TDM of the main immunosuppressants used in thoracic transplantation is presented in this article. Even more so than in other solid organ transplant populations, their pharmacokinetics are characterized by wide intra- and interindividual variability in thoracic transplant recipients. The pharmacokinetics of ciclosporin in heart and lung transplant recipients have been explored in a number of studies, but less is known about the pharmacokinetics of mycophenolate mofetil and tacrolimus in these populations, and there are hardly any studies on the pharmacokinetics of sirolimus and everolimus. Given the increased use of these molecules in thoracic transplant recipients, their pharmacokinetics deserve to be explored in depth. There are very few data, some of which are conflicting, on the practices and outcomes of TDM of immunosuppressants after thoracic transplantation. The development of sophisticated TDM tools dedicated to thoracic transplantation are awaited in order to accurately evaluate the patients' exposure to drugs in general and, in particular, to immunosuppressants. Finally, large cohort TDM studies need to be conducted in thoracic transplant patients in order to identify the most predictive exposure indices and their target values, and to validate the clinical usefulness of improved TDM in these conditions. In part I of the article, we review the pharmacokinetics and TDM of calcineurin inhibitors. In part II, we will review the pharmacokinetics and TDM of mycophenolate and mammalian target of rapamycin inhibitors, and provide an overall discussion along with perspectives.

Mycophenolate blood level monitoring: recent progress

The concentration-effect relationship for mycophenolic acid (MPA), and the high variability in MPA concentrations in patients on standard dose mycophenolate mofetil (MMF) therapy, for some centers has provided enough evidence to implement therapeutic drug monitoring (TDM) for MMF in daily practice. Two randomized trials Adaption de Posologie du MMF en Greffe Renale (APOMYGRE) and fixed-dose versus concentration controlled (FDCC) investigated the added benefit of TDM for MMF in renal transplant recipients. The APOMYGRE study showed a significant reduction in the incidence of acute rejection in concentration-controlled patients, while the FDCC study had a negative outcome, despite a similar study design. Although it was expected that these prospective trials would give the final answer to the question of whether or not TDM for MMF would be of benefit, it seems that the studies have not had much impact on patient management. Several trials have shown the importance of early adequate exposure to MPA in the first week after transplantation. As it will be hard to improve MPA exposure with TDM, this early, ongoing study now investigates the use of an increased starting dose. The increased starting dose will avoid underexposure to MPA in higher proportions of patients shortly after transplantation but may result in more toxicity in patients with MPA exposures exceeding the upper threshold of the therapeutic window.

Models for the prediction of mycophenolic acid area under the curve using a limited-sampling strategy and an enzyme multiplied immunoassay technique in Chinese patients undergoing liver transplantation

BACKGROUND

An enzyme multiplied immunoassay technique (EMIT) provides convenient and accurate measurements of mycophenolic acid (MPA) concentrations for determination of immunosuppression during treatment with mycophenolate mofetil (MMF). No abbreviated model for estimating the full 12-hour MPA AUC using an EMIT assay in liver transplant recipients has been described previously.

OBJECTIVE

This study was conducted to determine the best model for predicting the MPA AUC using the EMIT method and a limited-sampling strategy in Chinese patients undergoing liver transplantation.

METHODS

The study enrolled consecutive liver transplant patients who were receiving MMF 1 g BID along with tacrolimus. A complete MPA pharmacokinetic profile was obtained for each patient on a single day, 7 to 14 days after transplantation. The EMIT method was used to determine MPA concentrations before dosing and at 0.5, 1, 1.5, 2, 4, 6, 8, 10, and 12 hours after dosing on the sampling day. Multiple linear regression analysis was used to evaluate potential models for estimating the full 12-hour MPA AUC. The accuracy and robustness of the models were evaluated using bootstrap analysis. Prediction error and prediction bias were calculated. Agreement between the estimated MPA AUC(0-12) and the full 12-hour MPA AUC was investigated using Bland-Altman analysis.

RESULTS

The study enrolled 48 Chinese liver transplant recipients (45 male, 3 female) with a mean (SD) age of 50 (12) years, mean weight of 64 (12) kg, and mean height of 169 (6) cm. Twenty-four models that included blood sampling at 1 through 4 time points were developed (r(2) = 0.015-0.950). Four models with the highest r(2) values were selected; the lack of significant differences from the original dataset on bootstrap analysis indicated acceptable accuracy and robustness. The best model for predicting the MPA AUC(0-12) employed concentrations at 1, 2, 4, and 8 hours; 40 of 48 (83.3%) MPA AUC(0-12) values estimated using this model were within 15% of the full 12-hour MPA AUC. This model had a minimal mean prediction error (mean [SD], 0.27% [1.79%]) and mean absolute prediction error (8.83% [1.24%]). On Bland-Altman analysis, this model also had the best agreement between the estimated MAP AUC(0-12) and the full 12-hour MPA AUC, with a mean error of 9.02 mg . h/L.

CONCLUSIONS

In this small group of Chinese liver transplant patients receiving MMF and concomitant tacrolimus, models for estimating the MPA AUC(0-12) were developed using the EMIT method and a limited-sampling strategy. The best model for prediction of the full 12-hour MPA AUC was 4.46 + 0.81 . C1 + 1.78 . C(2)+2.51.C(4)+4.94.C8.

A limited sampling strategy for estimating mycophenolic acid area under the curve in adult heart transplant patients treated with concomitant cyclosporine

OBJECTIVE

Heart transplantation studies have shown a relationship between the mycophenolic acid area under the curve (AUC) 0-12 h (MPA AUC(0-12h)) values and risk of acute rejection episodes and fewer side-effects in patient receiving cyclosporine during the first year post-transplant. However, measurement of full AUC is costly and time consuming and in this case it is an impractical approach to drug monitoring. Therefore, the authors describe a limited sampling strategy to estimate the MPA AUC(0-12h) value in adult heart transplant recipients.

METHODS

Ninety MPA pharmacokinetic (PK) profiles were studied. The samples were collected immediately before and 0.5, 1, 1.5, 2, 2.5, 3, 4, 6, 9, 12 h after the morning dose of mycophenolate mofetil (MMF) following an overnight fast. PK profiles were determined at 6-8 weeks, 6, 12 months and more than 1 year after transplantation. Using stepwise multiple linear regression analysis a sampling strategy from 60 of PK profiles was obtained and next the bias and precision of the model were evaluated in another 30 PK profiles.

RESULTS

The three-point model using C(0.5h), C(1h), C(2h) was found to be superior to all other models tested (r(2) = 0.841). The regression equation for AUC estimation which gave the best fit to this model is: 9.69 + 0.63C(0.5) + 0.61C(1) + 2.20C(2). Using that model 63 of the 90 (70%) full AUC values were estimated within 15% of their actual value. For the best-fit model, the mean prediction error was 3.2%, with 95% confidence intervals for prediction error to range from -42.2% to 40.3%. All other models which use one, two or three time-points over the first 2 h are poorer predictors of the full AUC than the model above.

CONCLUSION

The proposed three time-point equation to estimate AUC will be helpful in optimizing immunosuppressive therapy in heart transplantation.

Calcineurin inhibitor sparing in paediatric solid organ transplantation : managing the efficacy/toxicity conundrum

Despite their efficacy, the calcineurin inhibitors (CNIs) ciclosporin and tacrolimus carry a risk of debilitating adverse effects, especially nephrotoxicity, that affect the long-term outcome and survival of children who are given organ transplants. Simple reduction in dosage of CNI has little or no long-term benefit on their adverse effects, and complete withdrawal without threatening graft outcome may only be possible after liver transplantation. Until the last decade, the only option was to increase corticosteroid and/or azathioprine doses, which imposed additional long-term hazards. Considered here are the emerging generation of new agents offering an opportunity for improving long-term graft survival, minimizing CNI-related adverse events and ensuring patient well-being.A holistic, multifaceted strategy may need to be considered - initial selection and optimized use and monitoring of immunosuppressant regimens, early recognition of indicators of patient and graft dysfunction, and, where applicable, early introduction of CNI-sparing regimens facilitating CNI withdrawal. The evidence reviewed here supports these approaches but remains far from definitive in paediatric solid organ transplantation. Because de novo immunosuppression uses CNI in more than 93% of patients, reduction of CNI-related adverse effects has focused on CNI sparing or withdrawal.A recurring theme where sirolimus and mycophenolate mofetil have been used for this purpose is the importance of their early introduction to limit CNI damage and provide long-term benefit: for example, long-term renal function critically reflects that at 1 year post-transplant. While mycophenolic acid shows advantages over sirolimus in preserving renal function because the latter is associated with proteinuria, sirolimus appears the more potent immunosuppressant but also impairs early wound healing. The use of CNI-free immunosuppressant regimens with depleting or non-depleting antibodies plus sirolimus and mycophenolic acid needs much wider investigation to achieve acceptable rejection rates and conserve renal function. The adverse effects of the alternative immunosuppressants, particularly the dyslipidaemia associated with sirolimus, needs to be minimized to avoid replacing one set of adverse effects (from CNIs) with another. While we can only conjecture that judicious combinations with the second generation of novel immunosuppressants currently in development will provide these solutions, a rationale of low-dose therapy with multiple immunosuppressants acting by complementary mechanisms seems to hold the promise for efficacy with minimal toxicity until the vision of tolerance achieves reality.

Monitoring mycophenolic acid pharmacokinetic parameters in liver transplant recipients: prediction of occurrence of leukopenia

Mycophenolate mofetil (MMF) is a very powerful immunosuppressive drug used in preventing acute rejection in liver transplantation. However, MMF has some serious side effects, including hematologic and gastrointestinal disorders. This study was designed to investigate the relationship between the clinical events and the pharmacokinetics of mycophenolic acid (MPA) in Chinese liver transplant recipients. Sixty-three adult liver transplant recipients receiving 1.0 g of MMF twice daily in combination with tacrolimus were prospectively included. The MPA pharmacokinetic profiles (blood sampling time points: before the dose and 0.5, 1, 1.5, 2, 4, 6, 8, 10, and 12 hours after the dose) were monitored after transplantation. Every clinical event, including acute and MMF-related side effects, was monitored in all patients within 3 months. Two patients (3.2%) had an episode of acute rejection. Forty-two patients (66.7%) had 52 episodes of MMF-related side effects, including leukopenia, diarrhea, and infection. The 0-hour concentration (C(0h)), maximum (peak) concentration (C(max)), and area under the curve from 0 to 12 hours (AUC(0-12h)) in patients with side effects were significantly higher than those in patients without side effects (P < 0.05). The thresholds of side effects from receiver operating characteristic analysis were 2 mg/L (sensitivity, 52.4%; specificity, 90.5%) for C(0h), 10 mg/L (sensitivity, 45.2%; specificity, 85.7%) for C(max), and 40 mg h/L (sensitivity, 71.4%; specificity, 61.9%) for AUC(0-12h) (P < 0.05). Leukopenia was discriminated effectively in C(0h) and in C(max) (P < 0.05). These results demonstrate the close relationship between leukopenia and MPA pharmacokinetic parameters in the early period after liver transplantation. C(0h) and AUC(0-12h) of MPA could predict the subsequent occurrence of leukopenia. These values may be used in routine monitoring for MMF therapy.

Pharmacokinetics of mycophenolate mofetil and its glucuronide metabolites in healthy volunteers

We previously reported that polymorphisms in the UGT2B7 and UGT1A9 genes are associated with significant alteration in the disposition of mycophenolic acid (MPA) in healthy volunteers. Aim: This study further evaluates the impact of genetic polymorphisms at the UGT1A1, UGT1A7 and ABCC2 loci. Methods: Genetic analyses of five UGT candidate genes and ABCC2 were completed on 47 healthy subjects who received a single dose of 1.5 g mycophenolate mofetil and completed a 12-h pharmacokinetic profile. Results: Multivariate analyses indicate that the ABCC2 -24T promoter polymorphism is associated with a 25% increase in acyl mycophenolic acid phenolic glucuronide level. Subjects with combined ABCC2 -24T and UGT1A9*3 genotypes present a 169% increased exposure to AcMPAG. Homozygosity for UGT1A7 387G/391A (129Lys/131Lys) is associated with a modest but significant 7% reduction in MPA level. When these additional genetic factors are considered in the model, the effects of previously described UGT1A9 and UGT2B7 variations remain significant. No significant effect is observed for UGT1A1*28, UGT1A7 622T/C (Trp208Arg), UGT1A9 -440TC/-331CT, UGT1A9 -118 TA9/10 and seven other ABCC2 SNPs. Conclusion: We demonstrate that MPA disposition is a multigenic process, and that additional studies are required to ascertain the relationship between UGT, ABCC2 genotypes and MPA pharmacokinetics in transplant recipients.

Infectious, malignant, and autoimmune complications in pediatric heart transplant recipients

OBJECTIVE

To review clinical courses of pediatric heart transplant survivors after 5 years from transplantation for infections, lymphoproliferative, and autoimmune diseases.

STUDY DESIGN

A total of 71 patients were examined in 2 groups, infant recipients (underwent transplant <1 year of age, n = 38) and older recipients (underwent transplant >1 year, n = 33). All patients received comparable immunosuppression. Calculated occurrence rates were reported as means per 10 years of follow-up with SEs. Differences were examined by using Poisson regression.

RESULTS

Infant recipients had significantly higher (P < .001) occurrence rates of severe (mean, 2.04 +/- 0.5) and chronic infections (mean, 4.58 +/- 0.67) compared with older recipients (means, 0.37 +/- 0.19 and 1.87 +/- 0.70, respectively). Types of infections were similar to those in the general population with extremely rare opportunistic infections; however, they were more severe and resistant to treatment. Autoimmune disorders occurred at a frequency comparable with lymphoproliferative diseases and were observed in 7 of 38 infants (18%). Most common were autoimmune cytopenias.

CONCLUSIONS

Infant heart transplant recipients who survive in the long term have higher occurrence rates of infections compared with older recipients. Autoimmune disorders are a previously unrecognized morbidity in pediatric heart transplantation.

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.

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.

Clinical pharmacokinetics and pharmacodynamics of mycophenolate in solid organ transplant recipients

This review aims to provide an extensive overview of the literature on the clinical pharmacokinetics of mycophenolate in solid organ transplantation and a briefer summary of current pharmacodynamic information. Strategies are suggested for further optimisation of mycophenolate therapy and areas where additional research is warranted are highlighted. Mycophenolate has gained widespread acceptance as the antimetabolite immunosuppressant of choice in organ transplant regimens. Mycophenolic acid (MPA) is the active drug moiety. Currently, two mycophenolate compounds are available, mycophenolate mofetil and enteric-coated (EC) mycophenolate sodium. MPA is a potent, selective and reversible inhibitor of inosine monophosphate dehydrogenase (IMPDH), leading to eventual arrest of T- and B-lymphocyte proliferation. Mycophenolate mofetil and EC-mycophenolate sodium are essentially completely hydrolysed to MPA by esterases in the gut wall, blood, liver and tissue. Oral bioavailability of MPA, subsequent to mycophenolate mofetil administration, ranges from 80.7% to 94%. EC-mycophenolate sodium has an absolute bioavailability of MPA of approximately 72%. MPA binds 97-99% to serum albumin in patients with normal renal and liver function. It is metabolised in the liver, gastrointestinal tract and kidney by uridine diphosphate gluconosyltransferases (UGTs). 7-O-MPA-glucuronide (MPAG) is the major metabolite of MPA. MPAG is usually present in the plasma at 20- to 100-fold higher concentrations than MPA, but it is not pharmacologically active. At least three minor metabolites are also formed, of which an acyl-glucuronide has pharmacological potency comparable to MPA. MPAG is excreted into the urine via active tubular secretion and into the bile by multi-drug resistance protein 2 (MRP-2). MPAG is de-conjugated back to MPA by gut bacteria and then reabsorbed in the colon. Mycophenolate mofetil and EC-mycophenolate sodium display linear pharmacokinetics. Following mycophenolate mofetil administration, MPA maximum concentration usually occurs in 1-2 hours. EC-mycophenolate sodium exhibits a median lag time in absorption of MPA from 0.25 to 1.25 hours. A secondary peak in the concentration-time profile of MPA, due to enterohepatic recirculation, often appears 6-12 hours after dosing. This contributes approximately 40% to the area under the plasma concentration-time curve (AUC). The mean elimination half-life of MPA ranges from 9 to 17 hours. MPA displays large between- and within-subject pharmacokinetic variability. Dose-normalised MPA AUC can vary more than 10-fold. Total MPA concentrations should be interpreted with caution in patients with severe renal impairment, liver disease and hypoalbuminaemia. In such individuals, MPA and MPAG plasma protein binding may be altered, changing the fraction of free MPA available. Apparent oral clearance (CL/F) of total MPA appears to increase in proportion to the increased free fraction, with a reduction in total MPA AUC. However, there may be little change in the MPA free concentration. Ciclosporin inhibits biliary excretion of MPAG by MRP-2, reducing enterohepatic recirculation of MPA. Exposure to MPA when mycophenolate mofetil is given in combination with ciclosporin is approximately 30-40% lower than when given alone or with tacrolimus or sirolimus. High dosages of corticosteroids may induce expression of UGT, reducing exposure to MPA. Other co-medications can interfere with the absorption, enterohepatic recycling and metabolism of mycophenolate. Most pharmacokinetic investigations of MPA have involved mycophenolate mofetil rather than EC-mycophenolate sodium therapy. In population pharmacokinetic studies, MPA CL/F in adults ranges from 14.1 to 34.9 L/h (ciclosporin co-therapy) and from 11.9 to 25.4 L/h (tacrolimus co-therapy). Patient bodyweight, serum albumin concentration and immunosuppressant co-therapy have a significant influence on CL/F. The majority of pharmacodynamic data on MPA have been obtained in patients receiving mycophenolate mofetil therapy in the first year after kidney transplantation. Low MPA AUC is associated with increased incidence of biopsy-proven acute rejection. Gastrointestinal adverse events may be dose related. Leukopenia and anaemia have been associated with high MPA AUC, trough concentration and metabolite concentrations in some, but not all, studies. High free MPA exposure has been identified as a risk factor for leukopenia in some investigations. Targeting a total MPA AUC from 0 to 12 hours (AUC12) of 30-60 mg.hr/L is likely to minimise the risk of acute rejection and may reduce toxicity. IMPDH monitoring is in the early experimental stage. Individualisation of mycophenolate therapy should lead to improved patient outcomes. MPA AUC12 appears to be the most useful exposure measure for such individualisation. Limited sampling strategies and Bayesian forecasting are practical means of estimating MPA AUC12 without full concentration-time profiling. Target concentration intervention may be particularly useful in the first few months post-transplant and prior to major changes in anti-rejection therapy. In patients with impaired renal or hepatic function or hypoalbuminaemia, free drug measurement could be valuable in further interpretation of MPA exposure.

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.

Therapeutic Drug Monitoring of Mycophenolic Acid in Solid Organ Transplant Patients Treated With Mycophenolate Mofetil: Review of the Literature

Mycophenolate mofetil (MMF) has conventionally been administered at a fixed dose without routinely monitoring blood levels of mycophenolic acid (MPA), the active metabolite. The contribution of therapeutic drug monitoring (TDM) during MMF therapy remains controversial. A literature review was performed to explore the usefulness of TDM for MPA in solid organ transplantation. In addition, emphasis was placed on the potential clinical benefits and limitations of TDM for MPA. Available studies have limitations and report conflicting results. Although early after transplantation MPA area under the curve might have predictive value for the risk of acute rejection, predose levels appear less reliable. With regard to MPA toxicity, most studies showed no correlation between MPA pharmacokinetics and adverse effects. TDM is hampered by several factors such as the considerable intra-subject variability of MPA pharmacokinetics and the increasing number of different drug combinations. Proposed target ranges are restricted to the early posttransplant period when MMF is used in combination with cyclosporine. The current review of the literature indicates no clear support for a substantial clinical benefit of TDM and more data from prospective randomized trials are needed.

Therapeutic drug monitoring of mycophenolate mofetil in transplantation

A roundtable meeting to discuss the use of therapeutic drug monitoring (TDM) to guide immunosuppression with mycophenolate mofetil was held in New York in December 2004. Existing recommendations for the initial months after transplantation were updated. After ensuring adequate levels of mycophenolic acid (MPA, the active metabolite of mycophenolate mofetil) immediately after transplantation, optimal efficacy may require only a few dose adjustments, because intrapatient variability in exposure seems low. Recommendations based on current knowledge were made for posttransplantation sampling time points and for target MPA concentrations. Algorithms for estimating MPA exposure using limited sampling strategies were presented, and a new assay for MPA discussed. It was agreed that because of interpatient variability and the influence of concomitant immunosuppressants, TDM might help optimize outcomes, especially in patients at higher risk of rejection. The value of TDM in the general transplant population will be assessed from large, ongoing, randomized studies.

Sequential Determination of Pharmacokinetics and Pharmacodynamics of Mycophenolic Acid in Liver Transplant Patients Treated with Mycophenolate Mofetil

BACKGROUND

In liver transplantation, mycophenolate mofetil (MMF) is habitually administered using fixed doses. We assessed whether mycophenolic acid (MPA) monitoring could be advisable in liver transplant patients.

METHODS

In 15 liver transplant patients receiving tacrolimus, daclizumab and MMF (1 g bid, orally), we determined the 12-hour plasma MPA pharmacokinetic profile after one dose of MMF at days 6, 10, and 16, and months 3 and 6. The inhibitory capacity of serum MPA on proliferation of CEM cells, a cell line insensitive to other immunosuppressants, was also determined.

RESULTS

A large interindividual variability in MPA profiles was observed at any time. Regardless of a gradual increase in individual MPA AUC and C(0) over time following transplantation, a substantial proportion of patients had these parameters below the ranges recommended in other organ transplantations throughout the study. When MPA AUC and C(0) were within the recommended ranges, CEM proliferation was inhibited by almost all serum samples, but when these pharmacokinetic parameters were below the recommended ranges, CEM proliferation was very variable and, therefore, unpredictable. No relationship between MPA pharmacokinetics and the efficacy of MMF could be established (only one patient developed rejection), probably due to the concomitant administration of tacrolimus and daclizumab. Gastrointestinal symptoms were the only adverse events with a significant relationship with MPA levels.

CONCLUSIONS

During the first postoperative months, exposure to MPA is low in a considerable proportion of liver transplant patients receiving MMF at a fixed dose of 1 g bid. MPA monitoring appears necessary in these patients.

Mycophenolic acid 12-h trough level monitoring in renal transplantation: association with acute rejection and toxicity

Studies of renal transplantation utilizing trough plasma level monitoring of mycophenolic acid (MPA) have shown inconsistent associations with toxicity and rejection. In this study, 5600 12-h trough MPA samples from 121 renal transplant recipients immunosuppressed with mycophenolate mofetil (MMF) and tacrolimus in a steroid sparing protocol (steroids for 7 days only) were sequentially analyzed. Higher MPA levels were associated with lower hemoglobin concentrations and anemia (hemoglobin <10 g/dL). Similarly, higher MPA levels were associated with lower total white cell counts and an increased incidence of leucopenia (total white cell count <4.0 x 10(9)/L). Hypoalbuminemia and renal impairment were also associated with hemotoxicity. MMF-associated diarrhea and viral infection were associated with higher MPA levels. Conversely, biopsy-proven acute rejection within the first month post-transplantation was associated with lower MPA levels. Anti-CD25 antibody induction was also associated with reduced rejection rates. No association was seen between MPA levels and platelet count, thrombocytopenia or bacterial infection. An MPA level of 1.60 mg/L early post-transplantation best discriminated patients with and without rejection, and an MPA level of 2.75 mg/L best discriminated patients with and without toxicity later post-transplantation.

Influence of co-medication with sirolimus or cyclosporine on mycophenolic acid pharmacokinetics in kidney transplantation

The pharmacokinetics of mycophenolic acid (MPA)--the active metabolite of mycophenolate mofetil (MMF)--is significantly influenced by co-medications. The impact of sirolimus on daily MPA exposure, however, has not been investigated so far. As a part of the study aimed at investigating the efficacy of Campath-1H induction therapy in a steroid-free regimen in kidney transplantation, MPA plasma levels were serially measured in 21 patients treated with low-dose sirolimus (SRL) or low-dose CsA both in addition to low-dose MMF over 12 months post-operatively. Full pharmacokinetic profiles were compared at month 6 and 12 post-surgery. Mean dose-adjusted MPA trough levels were 4.4-fold higher in patients on combined SRL and MMF than in those given CsA and MMF. Pharmacokinetic studies demonstrated that mean MPA C(max) and T(max) were comparable in the two groups, while mean MPA AUC(0-12) was higher in SRL than CsA treated patients. The pharmacokinetic profile of SRL- but not of CsA-group showed a second peak consistent with the enterohepatic recirculation of MPA. These findings suggest that SRL and CsA have different effects on MPA metabolism and/or excretion eventually affecting its immunosuppressive property and/or toxicity. CsA, but not SRL, inhibits MPA enterohepatic recirculation, reducing MPA daily exposure.

A phase I/II study of mycophenolate mofetil in combination with cyclosporine for prophylaxis of acute graft-versus-host disease after myeloablative conditioning and allogeneic hematopoietic cell transplantation

Abstract In a phase I/II study, the combination of cyclosporine (CSP) and mycophenolate mofetil (MMF) was investigated as graft-versus-host disease (GVHD) prophylaxis after myeloablative conditioning and hematopoietic cell transplantation from an HLA-matched sibling donor. In phase I, 3 groups, each with 10 or 11 patients, received MMF (15 mg/kg) from day 0 to day 27 at decreasing dose intervals of every 12, 8, and 6 hours to determine a safe and effective total daily dose. At the 45 mg/kg/d dosage level, 4 of 11 patients developed only grade II GVHD, and a concentration at steady state of mycophenolic acid (the active moiety of MMF) consistent with a therapeutic range described for solid-organ transplantation was achieved. There was a suggestion of increased toxicity without improved efficacy at the 60 mg/kg/d dosage level. Accordingly, the 45 mg/kg/d dosage was therefore selected for phase II, and another 15 patients were added to this group from the phase I study (n=26). The concentrations at steady state for this dosage at days 0, 6, 13, 20, and 27 were 2.73, 3.02, 3.20, 2.62, and 2.64 microg/mL, respectively. No toxicities were attributed to MMF at this dose. The median time to engraftment after hematopoietic cell transplantation was 15 days (range, 10-20 days). The incidence of acute GVHD was 62%, which was comparable to a group of historical controls receiving CSP and methotrexate (MTX) for GVHD prophylaxis. Although a significant improvement in the prevention of GVHD was not suggested, compared with CSP and MTX, MMF in combination with CSP could be considered in cases in which MTX is contraindicated.

Review of Major Clinical Trials with Mycophenolate Mofetil in Cardiac Transplantation

Over the past 10 years, the addition of mycophenolate mofetil (MMF) to combination immunosuppressive regimens in cardiac transplant patients has resulted in significant outcomes benefits. Randomized trials and other studies have demonstrated that the use of MMF is associated with a decreased risk of rejection and improved survival. This article will provide an overview of these trials, as well as those evaluating MMF in renal-sparing regimens and in pediatric cardiac transplant recipients. In addition, emerging evidence demonstrating that MMF may provide long-term benefits in reducing cardiac allograft vasculopathy and those evaluating the role of MMF therapeutic drug monitoring in cardiac transplant recipients will be discussed.

Best Single Time Points to Predict the Area-Under-the-Curve in Long-Term Heart Transplant Patients Taking Mycophenolate Mofetil in Combination with Cyclosporine or Tacrolimus

BACKGROUND

The use of C2 levels for therapeutic drug monitoring (TDM) of cyclosporine microemulsion (CsA) has been clinically validated. Routine TDM of tacrolimus and mycophenolate mofetil (MMF) is based on trough (C0) levels and side effects, respectively. The purpose of the present study was to determine the best single time points to assess the area-under-the-curve (AUC(0-12 hours)) in long-term heart transplant patients being treated with MMF in combination with CsA or tacrolimus.

METHODS

We studied the AUC(0-12 hours) in long-term (>1 year), adult heart transplant patients being treated with CsA and MMF (14 patients) and with tacrolimus and MMF (9 patients).

RESULTS

C2 is the best surrogate (r2 = 0.87) of CsA AUC(0-12 hours). Tacrolimus C1 (r2 = 0.78), C2 (r2 = 0.83), C3 (r2 = 0.89) and C4 (r2 = 0.92) correlate better than C0 (r2 = 0.51) with the AUC(0-12 hours). When MMF is combined with CsA, there is poor correlation (r2) of MPA at all measured time points (C0 = 0.49, C2 = 0.09, C3 = 0.23, C4 = 0.44, and C6 = 0.60). When MMF is combined with tacrolimus, MPA C2 (r2 = 0.72), C4 (r2 = 0.86), C6 (r2 = 0.85), and C8 (r2 = 0.93) are better surrogates of the AUC(0-12 hours) compared with C0 (r2 = 0.69).

CONCLUSION

Our results suggest that in long-term heart transplant patients, the calcineurin inhibitor used in combination with MMF affects the correlation between MPA single time points and the AUC(0-12 hours). Future studies should determine the clinical benefit of TDM of tacrolimus and MPA with C2 or C4 compared with C0 and determine the therapeutic ranges. As for CsA-treated patients, CsA TDM should be performed with C2, and the TDM of MMF may be clinically irrelevant.

The Rationale for and Limitations of Therapeutic Drug Monitoring for Mycophenolate Mofetil in Transplantation

The addition of mycophenolate mofetil (MMF) to calcineurin inhibitor-based regimens reduces the incidence of acute rejection after kidney transplantation. The interpatient variability, changes over time of pharmacokinetic parameters, and the potential for drug interactions make the systemic exposure of mycophenolic acid (MPA) unpredictable at a fixed-dose regimen. An increase in plasma concentration of MPA significantly correlates with a decreased likelihood of an acute rejection after kidney or heart transplantation; therefore, a strategy of therapeutic drug monitoring for MMF therapy could improve outcome. Two large randomized, multicenter, prospective trials investigating the added value of therapeutic drug monitoring for MPA, by comparing fixed-dose treatment with concentration-controlled MMF treatment in kidney transplant recipients, are currently ongoing. More data are needed to fully establish the meaning of the reported prognostic value of preoperative inosine monophosphate dehydrogenase (IMPDH) activity, and longitudinal studies monitoring IMPDH activity after transplantation are eagerly awaited.

The Use of Systemic Immune Moderators in Dermatology: An Update

In addition to corticosteroids, dermatologists have access to an array of immunomodulatory therapies. Azathioprine, cyclophosphamide, methotrexate, cyclosporine, and mycophenolate mofetil are the systemic immunosuppressive agents most commonly used by dermatologists. In addition, new developments in biotechnology have spurred the development of immunobiologic agents that are able to target the immunologic process of many inflammatory disorders at specific points along the inflammatory cascade. Alefacept, efalizumab, etanercept, and infliximab are the immunobiologic agents that are currently the most well known and most commonly used by dermatologists. This article reviews the pharmacology, mechanism of action, side effects, and clinical applications of these therapies.

The V-Twin system (Dade Behring Laboratories): A useful tool for immunosuppressive drug monitoring

The predose trough cyclosporine (CsA) level (C0) was widely used to assess the possibility of drug nephrotoxicity. Owing to its potential limitation as an indicator of total drug exposure, 2-hour postdose (C2) monitoring has been considered to be a more accurate marker. The V-Twin analyzer (Vital SC, Netherlands) conceived for EMIT technologies (Dade Behring Laboratories) is proposed herein to determine CsA levels using a specific calibrator without any dilution, as well as tacrolimus (FK) and mycophenolate mofetil (MMF) levels. Both CsA (C0: n = 133 and C2: n = 55) and FK (n = 121) EMIT assays were compared to the RIA CsA assay (DiaSorin Laboratory) and to the MEIA tacrolimus assay (Abbott Laboratory), respectively. In addition, the feasibility of MMF EMIT assay was evaluated. Overall, 309 transplant patients were included in this study. For all parameters tested, total imprecision studies were lower than 10%, and the coefficient of linearity was r(2) > .99. For the CsA kit, the range of linearity was between 25 and 500 ng/mL for the C0 and 400 and 2000 ng/mL for the C2 assay. The values obtained were highly correlated with the RIA for the C0 levels (EMIT = 0.9 RIA+3.66; r = .97) and for the C2 levels (EMIT = 0.89 RIA-14.2; r = .956). Similar results were obtained with the EK EMIT kit, with a linearity range between 3 and 30 ng/mL, and a high concordance with the MEIA test (EMIT = 0.98 RIA+1.09; r = .96). Preliminary MMF results in 59 sera, containing from 0.1 to 30 microg/mL, showed that this examination could be included as a routine. The V-twin system is a useful tool for routine monitoring with a single method for C0 and C2 cyclosporine, tacrolimus, and mycophenolate levels.

Lack of correlation between MMF dose and MPA level in pediatric and young adult cardiac transplant patients: does the MPA level matter?

To determine the correlation between mycophenolate mofetil (MMF) dose and mycophenolic acid (MPA) level as well as its impact on rejection among young cardiac transplant recipients (OHT), trough concentrations of MPA and its metabolite, mycophenolic acid glucuronide (MPAG), were measured following MMF doses of 1200 mg/m2/d (max 3000 mg/d). Corresponding endomyocardial biopsy (EMB) grades and calcineurin inhibitor levels were recorded with simultaneous MPA/MPAG levels. Correlation coefficients were derived between MMF dose and MPA/MPAG levels. Contingency analysis evaluated the relation between MPA level and EMB score. Twenty-six patients (median age 15.4 years) had 120 MPA/MPAG levels measured. Average MMF dose was 1208.8 mg/m2/d with median MPA and MPAG concentrations: 2.1 (therapeutic: 1.0-3.5 microg/mL) and 48 microg/mL (reference range: 35-100 microg/mL), respectively. Only 50% of patients consistently achieved therapeutic levels with standard dosing. No correlation was found between MMF dose and MPA/MPAG levels. In the presence of therapeutic calcineurin inhibition, EMB grade > or = 2 occurred more with MPA concentrations < 2.5 microg/mL (p = 0.01). In young OHT patients, MMF dose does not correlate with MPA/MPAG levels, and standard MMF dosing fails to consistently achieve 'therapeutic' MPA concentrations. An MPA trough level < 2.5 microg/mL was more frequently associated with EMB grade > or = 2. Concentration rather than dose-driven management is a more prudent strategy when using MMF.

Using Established Immunosuppressant Therapy Effectively

Getting the most effective use of immunosuppressant medications in transplant patients continues to be a major challenge in clinical practice. This need applies to established immunosuppressants just as it does to new agents. In this review this principle is illustrated for mycophenolic acid, the active metabolite of mycophenolate mofetil, the most commonly used immunosuppressant, in various combinations with other immunosuppressants, in current clinical practice. Defining, as rigorously as possible, the requirements for effective therapeutic monitoring of MPA is an important goal given all of the changes in immunosuppressive drug regimens. This review will focus on the major factors known to influence MPA clearance including: UDP-glucuronyltransferases, enterohepatic circulation, MPA free fraction, the effect of time posttransplantation, concomitant administration of immunosuppressant drugs. The significant variability of MPA pharmacokinetics and the need to deepen our understanding of the influence of these factors on MPA clearance are strong reasons why additional clinical trials are needed to define best practice therapeutic drug monitoring of this drug.

Monitoring mycophenolate in liver transplant recipients: toward a therapeutic range

Predose plasma mycophenolic acid (MPA) concentrations measured with a semi-automated enzyme-multiplied immunoassay were related to adverse events (e.g., rejection, leukopenia, infection), drug dose, and clinical status in 147 adult and 63 pediatric liver allograft recipients receiving adjunctive immunosuppression with mycophenolate mofetil (MMF). In 12 of 13 acute rejection episodes, predose MPA levels were below the 1 mg/L cut-off defined using receiver operating characteristic (ROC) curve analysis. The relative risk of developing infection or leukopenia increased more than 3-fold above predose MPA levels of 3 to 4 mg/L. Plasma MPA levels correlated weakly (r2 = 0.081) with MMF dose and the dose / level relationship was variably influenced by age, the indication for MMF, concentrations of serum albumin and creatinine, and comedication with tacrolimus or cyclosporine. The median mycophenolate dose required per unit mycophenolate level was 50% lower in children than in adults. Comparable drug requirements were also decreased by renal dysfunction (by 40 and 43% in adults and children, respectively), and in patients prescribed MMF alone rather than with tacrolimus or cyclosporine. However, in patients with serum albumin less than 35 g/L, MMF dose requirements were higher than in those with normal albumin levels (by 2.1- and 2.6-fold in adults and children, respectively). In adults, 44.7% achieved clinically acceptable therapeutic MPA concentrations at a dose less than 1 g MMF twice daily and only 6.3% required 1.5 g twice daily as suggested by the manufacturer. The immunoassay was a rapid, reliable, and acceptably precise technique in which only 10.8% of measurements were unproductive. In conclusion, our data suggests that MPA predose level monitoring is both clinically- and cost-effective and that a therapeutic range of 1 to 3.5mg/L (by immunoassay) is applicable in liver allograft recipients given adjunctive MMF.