Monitoring of mycophenolic acid in pediatric renal transplant recipients

Efficacy and Safety of Mycophenolate Mofetil In De Novo Renal Transplantation in a Retrospective Cohort of Transplant Recipients in Colombia-Esmitren Study

BACKGROUND

To describe and establish the efficacy and safety of Mycophenolate Mofetil (Micoflavin) in patients with de novo renal transplantation during one-year post-transplant follow-up. As secondary objectives, the behavior of mycophenolic acid (MPA) C0 levels in this population, the relationship between MPA levels and renal function of the grafts, the incidence of acute rejection, and the incidence of adverse effects were evaluated.

METHODS

A prospective cohort study was conducted on patients who received a first kidney transplant from a deceased donor between March 1, 2021, and February 28, 2022, at the Alma Mater of Antioquia Hospital of the Antioquia's University, in Medellín, Colombia. MPA C0 levels were taken from the patients on days 15, 30, 90, 180, and 360 after the kidney transplantation.

RESULTS

Patients presented MPA therapeutic levels in the study. The average of the MPA levels in the population was 2.5 µg/mL, with an IQR of 2.13 to 3.32. There were 5 acute rejections (27%), but none of the patients with acute rejection presented subtherapeutic levels of mycophenolate. No significant relationship was observed between mycophenolic acid levels and rejection (P = .255). The patients who completed the study had no gastrointestinal intolerance to mycophenolate, cytomegalovirus infections, or significant hematological complications.

CONCLUSIONS

MMF (Micoflavin) maintained mycophenolic acid levels C0 within the therapeutic range, was well tolerated and without the presence of significant adverse events, and maintained stable renal function throughout the follow-up period in the population studied.

Mycophenolic Acid Trough Concentration and Dose Are Associated with Hematologic Abnormalities but Not Rejection in Kidney Transplant Recipients

BACKGROUND

Little is known regarding the safe fixed dose of mycophenolic acid (MPA) for preventing biopsy-proven acute rejection (BPAR) in kidney transplant recipients (KTRs). We investigated the correlation of MPA trough concentration (MPA C₀) and dose with renal transplant outcomes and adverse events.

METHODS

This study included 79 consecutive KTRs who received MPA with tacrolimus (TAC) and corticosteroids. The MPA C₀ of all the enrolled KTRs was measured, which was determined monthly by using particle-enhanced turbidimetric inhibition immunoassay for 12 months, and clinical data were collected at each time point. The clinical endpoints included BPAR, any cytopenia, and BK or cytomegalovirus infections.

RESULTS

No differences in MPA C₀ and dose were observed between KTRs with or without BPAR or viral infections under statistically comparable TAC concentrations. MPA C₀ was significantly higher in patients with leukopenia (P = 0.021) and anemia (P = 0.002) compared with those without cytopenia. The MPA dose was significantly higher in patients with thrombocytopenia (P = 0.002) compared with those without thrombocytopenia. MPA C₀ ≥ 3.5 μg/mL was an independent risk factor for leukopenia (adjusted odds ratio [AOR], 3.80; 95% confidence interval [CI], 1.24-11.64; P = 0.019) and anemia (AOR, 5.90; 95% CI, 1.27-27.51; P = 0.024). An MPA dose greater than the mean value of 1,188.8 mg/day was an independent risk factor for thrombocytopenia (AOR, 3.83; 95% CI, 1.15-12.78; P = 0.029). However, an MPA dose less than the mean value of 1,137.3 mg/day did not increase the risk of BPAR.

CONCLUSION

Either a higher MPA C₀ or dose is associated with an increased risk of cytopenia, but neither a lower MPA C₀ nor dose is associated with BPAR within the first year of transplantation. Hence, a reduced MPA dose with TAC and corticosteroids might be safe in terms of reducing hematologic abnormalities without causing rejection.

Polymorphisms in type I and II inosine monophosphate dehydrogenase genes and association with clinical outcome in patients on mycophenolate mofetil

BACKGROUND

Type I and II inosine monophosphate dehydrogenases (IMPDH) are the targets of mycophenolic acid (MPA), a widely used immunosuppressant. The aims of this study were: to check the presence of controversial polymorphisms in the IMPDH II gene; to look for new ones; and to investigate potential associations between the most frequent SNPs in both IMPDH genes and clinical outcome in renal transplant recipients.

METHODS

The DNA and clinical data of 456 patients from two clinical trials were collected. We sequenced the IMPDH II gene in 80 patients and we genotyped the 456 patients' DNA for the IMPDH II rs4974081, rs11706052, 787C>T and the IMPDH I rs2278293 and rs2278294 SNPs, all of which were earlier reported to be potentially involved in MPA treatment related outcome. We investigated the associations of biopsy proven acute rejection (BPAR), leucopenia, cytomegalovirus infections and other infections with these IMPDH polymorphisms, as well as with demographic, biological and treatment data using multivariate analysis.

RESULTS

Many IMPDH II variant alleles referenced in Genbank were not detected and no new polymorphisms were identified. In the whole group of 456 patients, the IMPDH I rs2278294 SNP was associated with a lower risk of BPAR and a higher risk of leucopenia over the first year post-transplantation. No other IMPDH I or IMPDH II polymorphism was significantly associated with any clinical outcome. Interestingly, calcineurin inhibitor and MPA exposures below the therapeutic range increased the risk of BPAR. Cytomegalovirus infection was the factor most closely linked with leucopenia, whereas tacrolimus was associated with fewer infections than cyclosporine.

CONCLUSION

IMPDH II genotyping may not improve MPA treatment outcome over the first year post-transplantation, in contrast to MPA and calcineurine inhibitor therapeutic drug monitoring and IMPDH I genotyping.

Pharmacokinetics and pharmacodynamics of mycophenolic acid and their relation to response to therapy of childhood-onset systemic lupus erythematosus

OBJECTIVES

Mycophenolic acid (MPA) is the active form of mycophenolate mofetil (MMF), which is currently used off-label as immunosuppressive therapy in childhood-onset SLE (cSLE). The objectives of this study were to (1) characterize the pharmacokinetics (MPA-PK) and pharmacodynamics (MPA-PD) of MPA and (2) explore the relationship between MPA-PK and cSLE disease activity.

METHODS

MPA-PK [area under the curve from 0-12 hours (AUC(0-12))] and MPA-PD [inosine-monophosphate dehydrogenase (IMPDH) activity] were evaluated in cSLE patients on stable MMF dosing. Change in SLE disease activity while on MMF therapy was measured using the British Isles Lupus Assessment Group (BILAG) index.

RESULTS

A total of 19 AUC(0-12) and 10 IMPDH activity profiles were included in the analysis. Large interpatient variability in MPA exposure (AUC(0-12)) was observed (mean ± SE: 32 ± 4.2 mg h/L; coefficient of variation: 57%). Maximum MPA serum concentrations coincided with maximum IMPDH inhibition. AUC(0-12) and weight-adjusted MMF dosing were only moderately correlated (r = 0.56, P = 0.01). An AUC(0-12) of ≥30 mg h/L was associated with decreased BILAG scores while on MMF therapy (P = 0.002).

CONCLUSION

Weight-adjusted MMF dosing alone does not reliably allow for the prediction of exposure to biologically active MPA in cSLE. Individualized dosing considering MPA-PK appears warranted as this allows for better estimation of immunologic suppression (IMPDH activity). Additional controlled studies are necessary to confirm that an MPA AUC(0-12) of at least 30 mg h/L is required for cSLE improvement.

Bioequivalence and pharmacokinetic comparison of two mycophenolate mofetil formulations in healthy Chinese male volunteers: an open-label, randomized-sequence, single-dose, two-way crossover study

BACKGROUND

Mycophenolate mofetil (MMF) is an ester prodrug of mycophenolic acid (MPA), so clinical studies measure the circulating plasma MPA concentration instead of MMF. MPA is extensively glucuronidated by several uridine diphosphate glycosyltransferases into an inactive 7-O-glucuronide and a pharmacologically active acylglucuronide. Considering the effect of racial differences and genetic factors on the pharmacokinetic (PK) properties of drugs, it is necessary to study them in Chinese populations.

OBJECTIVES

The aim of this study was to compare the clinical bioequivalence and PK properties of a test (dispersible tablets) and reference (capsules) formulation of MMF 1.0 g in healthy Chinese volunteers. We also established a validated HPLC method for the determination and quantification of MPA in human plasma. The study was required to obtain Chinese regulatory approval for the test formulation.

METHODS

This open-label, randomized-sequence, single-dose, 2-way crossover study was conducted at the First Hospital of Nanjing Medical University, Nanjing, China. Eligible subjects were healthy male volunteers who were randomly assigned at a 1:1 ratio to receive a single 1.0-g dose of the test or reference formulation, followed by a 1-week washout period and administration of the alternate formulation. The plasma concentration of MPA, which is the active metabolite of MMF, was determined using a validated HPLC method. For analysis of PK properties, blood samples were collected at 0, 10, 20, 30, and 45 minutes, and 1, 1.5, 3, 5, 8, 11, 18, 36, and 48 hour(s). The PK parameters, including C(max), T(max), t((1/2)), AUC(0-48), and AUC(0-infinity), were determined from the plasma concentrations of the 2 formulations by noncompartmental analysis. Tolerability was assessed at baseline (be- fore administration) and at 30 minutes and 1, 5, 18, and 48 hours after administration by monitoring vital signs. Laboratory tests (hematology, blood biochemistry, hepatic function, and urinalysis) were performed for the identification of adverse events (AEs) (eg, leukopenia, thrombocytopenia, anemia). Patient interviews were conducted to assess the occurrence of AEs such as diarrhea, abdominal pain, nausea, vomiting, and secondary infections. The formulations were considered to meet the regulatory requirements of bioequivalence if the log-transformed ratios of C(max) and AUC were within the predetermined equivalence range (80%-125%) as established by the US Food and Drug Administration (FDA).

RESULTS

Eighteen healthy Chinese male volunteers (mean [range] age, 23.5 [22-30] years; weight, 63.3 [56-68] kg; height, 171 [165-184] cm) were enrolled and completed the study. The main PK parameters of the MMF test and reference formulations were as follows: mean (SD) T(max), 0.68 (0.21) and 0.81 (0.18) hour, respectively; C(max), 25.58 (4.79) and 26.47 (3.67) mg/L; AUC(0-48), 59.19 (9.23) and 58.32 (9.28) mg/L/h; t((1/2)), 15.12 (3.17) and 16.04 (4.22) hours; AUC(0-infinity)), 63.28 (10.23) and 62.41 (10.28) mg/L/h. The mean (SD) relative bioavailability was 101.5% (10.3%). No statistically significant differences were found based on ANOVA. The ratios of C(max) (0.97) and AUC (1.01) for the test and reference formulations were within the FDA bioequivalence definition intervals of 80% to 125%. No AEs were reported by subjects or found on analysis of vital signs or laboratory tests.

CONCLUSIONS

In this study in healthy Chinese male volunteers, results from the PK analysis suggested that a single dose of the test and reference formulations of MMF 1.0 g met the regulatory requirements of bioequivalence, based on the FDA regulatory definition (rate and extent of absorption). Both formulations were well tolerated.

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.

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

STUDY OBJECTIVES

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

DESIGN

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

SETTING

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

PATIENTS

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

INTERVENTION

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

MEASUREMENTS AND MAIN RESULTS

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

CONCLUSION

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

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.

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.

The weight of pharmacokinetic parameters for mycophenolic acid in prediction of rejection outcome: the receiver operating characteristic curve analysis

Often the clinical researcher is confronted with the question of how accurate a particular laboratory test is to identify disease. To confirm the ability of pharmacokinetic (PK) parameters to discriminate between patients with or without acute rejection after kidney transplantation, an analysis of receiver operating characteristic (ROC) curves was performed in 51 adult patients, among whom nearly 50% experienced biopsy-proven acute rejection episodes during the first 90 days posttransplant. All patients received cyclosporine or tacrolimus, prednisone, and mycophenolate mofetil (MMF). The following PK variables were determined for mycophenolic acid, an active metabolite of MMF: predose (C(0)), maximum concentration (C(max)), and area under the concentration-time curve (AUC(0-12h)). ROC plots of sensitivity versus 1-specificity were generated to determine whether a particular PK parameter could discriminate renal transplant recipients with an acute rejection from those who experienced no rejection. Area under the ROC curves and the 95% confidence interval limits were calculated using the method of Hanley and McNeil. The C(0) and C(max) were less predictive values for acute rejection than AUC(0-12h). The AUC parameter appeared the most effective to discriminate an acute rejection episode during MMF therapy. This study indicated the utility of ROC curve analysis to select PK parameters to predict acute rejection episodes.