Mycophenolate Mofetil Pharmacokinetic Monitoring in Pediatric Kidney Transplant Recipients

The utility of trough mycophenolic acid levels for the management of lupus nephritis

Background

Monitoring of mycophenolic acid (MPA) levels may be useful for effective mycophenolate mofetil (MMF) dosing. However, whether commonly obtained trough levels are an acceptable method of surveillance remains debatable. We hypothesized that trough levels of MPA would be a poor predictor of area under the curve (AUC) for MPA.

Methods

A total of 51 patients with lupus nephritis who were on MMF 1500 mg twice a day and had a 4-h AUC done were included in this study. MPA levels were measured prior to (C0) and at 1 (C1), 2 (C2) and 4 (C4) h, followed by 1500 mg of MMF. The MPA AUC values were calculated using the linear trapezoidal rule. Regression analysis was used to examine the relationship between the MPA trough and AUC. Differences in the MPA trough and AUC between different clinical and demographic categories were compared using t-tests.

Results

When grouped by tertiles there was significant overlap in MPA, AUC 0-4 and MPA trough in all tertiles. Although there was a statistically significant correlation between MPA trough levels and AUC, this association was weak and accounted for only 30% of the variability in MPA trough levels. This relationship might be even more unreliable in men than women. The use of angiotensin-converting enzyme inhibitors or angiotensin receptor blockers was associated with increased MPA trough levels and AUC at 0-4 h (AUC0-4).

Conclusion

Trough levels of MPA do not show a strong correlation with AUC. In clinical situations where MPA levels are essential to guide therapy, an AUC0-4 would be a better indicator of the adequacy of treatment.

Enteric-coated mycophenolate sodium in de novo pediatric renal transplant patients

Data on the use of enteric-coated mycophenolic acid (EC-MPS) in pediatric transplantation cases are scarce. We undertook a 12-month, multicenter, open-label pilot study in which 16 de novo renal transplant patients aged 5-16 years received EC-MPS with cyclosporine A microemulsion (CsA-ME), steroids, and anti-interleukin-2 receptor antibody induction. The mean dose of EC-MPS was 916 +/- 93 mg/m(2) per day during weeks 1-2, 810 +/- 193 mg/m(2) per day during months 3-6, and 827 +/- 153 mg/m(2) per day during months 6-12. The mean CsA C(2) level exceeded target range up to month 6 post-transplant. Efficacy failure (biopsy-proven acute rejection, graft loss, death or loss to follow-up) occurred in two patients: one patient with primary non-function underwent nephrectomy, and one patient experienced biopsy-proven acute rejection (Grade 1B, day 344) following EC-MPS dose reduction. There were no deaths. Creatinine clearance (Schwartz) was 103 +/- 30 mL/min per 1.73 m(2) at month 6 and 100 +/- 16 mL/min per 1.73 m(2) at month 12. The majority of adverse events were mild or moderate (101/126, 80.2%). In this pilot study, EC-MPS 450 mg/m(2) administered twice daily with CsA, steroids, and interleukin-2 antibody induction resulted in a low rate of rejection with good renal function in a pediatric population. However, a larger, controlled trial is required to confirm these results.

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

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

Population pharmacokinetics of mycophenolic acid in senile Chinese kidney transplant recipients

To explore the pharmacokinetic characteristics of mycophenolic acid (MPA) among elderly Chinese kidney transplant recipients, we enrolled 24 patients over 60 years old (65.6 +/- 3.6) as the (Gs) group and 24 patients of 39.6 +/- 14.3 years old as a control group (Ga). Venous blood samples were taken at 0 (predose), 0.5, 1, 1.5, 2, 3, 4, 6, 8, 10, and 12 hours after the morning dose of mycophenolate mofetil at 10 to 12 weeks posttransplant. Plasma MPA concentrations were measured by a validated high-performance liquid chromatography method. Within 6-month posttransplant follow-up, there had not been an acute rejection episode when five elderly and one other adult experienced severe adverse events (SAEs), such as pneumonia and leukocytopenia. MPA area under the curve (AUC) in Gs was significantly lower than that among Ga (P < .05), while there was no significant difference in predose, peak concentrations, or peak times (P > .05). The concentration-time curve of Gs showed a bipeak pattern in five patients (20.8%) during the early stage (2 to 4 hours postdose). AUC in the subgroup of Gs with SAEs (n = 5) was significantly higher than that of elderly subjects without SAEs (n = 19) (P = .042). When Gs were subdivided at a cutting AUC point of 25 mug/mL, the SAE incidence was significantly higher in the subgroup with a higher AUC than than those with the lower AUC (P = .047). Through multiple stepwise regression, we obtained a minimal model to estimate MPA AUC of elderly recipients: AUC = 3.0410 + 9.8588 x C(0) + 0.5963 x C(0.5) + 2.5612 x C(3) (R(2) = .893).

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 reaches therapeutic levels whereas mycophenolate mofetil does not

BACKGROUND

In kidney transplanted children, it is difficult to obtain blood levels of mycophenolic acid between 2 and 4 microg/mL, when mycophenolate mofetil doses up to 30 mg/kg/d are given two or three times a day. We proposed that using mycophenolic acid, instead of the salt mycophenolate mofetil, may help us to reach target levels.

AIM

We sought to describe the pharmacokinetics of mycophenolic acid in eight kidney transplanted children over a period of 1.2 +/- 0.8 years.

PATIENTS AND METHODS

Eight patients (5 boys and 3 girls) aged 7.0 +/- 1.8 years received cadaveric kidney transplantations. Induction with basiliximab was followed by cyclosporine (n = 4) or tacrolimus (n = 4), tapered steroids (withdrawal at 12 months in six cases and maintained at 0.15 mg/kg/d in two cases), and mycophenolate mofetil (25 to 30 mg/kg/d two or three times a day). For 1.0 +/- 0.3 years mycophenolic acid levels were between 0.8 +/- 0.3 microg/mL. When mycophenolic acid sodium tablets were available, all patients were switched to this drug.

RESULTS

After the conversion, blood levels obtained at 8 +/- 3 days were 1.5 to 5.0 microg/mL (median, 3.2), which were far closer to the target 2 to 4 microg/mL. No gastrointestinal disorders were observed with the follow-up of 72 +/- 18 days.

CONCLUSION

Mycophenolic acid sodium reaches therapeutic levels whereas mycophenolate mofetil does not. If mycophenolic acid were available in syrup form, it could be used in patients under 5 years of age. It is necessary to follow these patients to rule out enzymatic induction.

Beyond cyclosporine: a systematic review of limited sampling strategies for other immunosuppressants

Therapeutic drug monitoring has gained much attention in the management of immunosuppressive therapy. Area under the plasma drug concentration-time curve (AUC) is the pharmacokinetic (PK) parameter most commonly used to assess total exposure to a drug. However, estimation of AUC requires multiple blood samples throughout the dosing period, which is often inconvenient and expensive. Limited sampling strategies (LSSs) are therefore developed to estimate AUC and other PK parameters accurately and precisely while minimizing the number of blood samples needed. This greatly reduces costs, labor and inconvenience for both patients and clinical staff. In the therapeutic management of solid organ transplantation, LSSs for cyclosporine are commonplace and have been extensively reviewed. Thus, this systematic review paper focuses on other immunosuppressive agents and categorizes the 24 pertinent citations according to the U.S. Preventive Services Task Force rating scale. Thirteen articles (3 level I, 1 level II-1, 2 level II-2, and 7 level III) involved LSSs for mycophenolate, 7 citations (1 level I and 6 level III) for tacrolimus (TAC), and 3 citations (all level III) for other drugs (sirolimus) or multiple drugs. The 2 main approaches to establishing LSSs, multiple regression and Bayesian analyses, are also reviewed. Important elements to consider for future LSS studies, including proper validation of LSSs, convenient sampling times, and application of LSSs to the appropriate patient population and drug formulation are discussed. Limited sampling strategies are a useful tool to help clinicians make decisions on drug therapy. However, patients' pathophysiology, environmental and genetic factors, and pharmacologic response to therapy, in conjunction with PK profiling tools such as LSSs, should be considered collectively for optimal therapy management.

Mycophenolate mofetil in the treatment of uveitis in children

BACKGROUND

Mycophenolate mofetil (MMF) is a new immunosuppressive agent that effectively controls the intraocular inflammation in adults.

PURPOSE

To assess the efficacy of MMF in uveitis in children and to analyse the possible side effects.

PARTICIPANTS AND METHODS

A retrospective analysis was carried out on 17 children (32 eyes) with intraocular inflammation treated with MMF and followed up at the University Eye Hospital Tuebingen, Tuebingen, Germany, between 2000 and 2005. All children had chronic non-infectious uveitis and received MMF for at least 6 months. All patients were given steroids or other immunosuppressive agents before initiating treatment with MMF.

RESULTS

17 children (10 boys and 7 girls) with a mean age of 8 (range 2-13) years at the onset of uveitis were examined. The average duration of follow-up after initiation of MMF was 3 (range 2-5) years. A steroid-sparing effect was achieved in 88% of the patients. The oral prednisolone was successfully discontinued in 41% children and reduced to a daily dose of < or =5 mg in 47% of the children. 24% of the patients remained relapse-free during the treatment, but a reduction in the relapse rate was observed in all other patients except one. Visual acuity was increased or maintained in 13 children (76%). Mild side effects (headache, rash, gastrointestinal discomfort) occurred in 7 patients (41%) and were the cause of discontinuation of MMF in 1 patient.

CONCLUSION

The results of our study are encouraging and suggest that MMF is an effective agent also in the treatment for uveitis in children, with marked steroid-sparing potential and an acceptable side effect profile.