Long-term changes in mycophenolic acid exposure in combination with tacrolimus and corticosteroids are dose dependent and not reflected by trough plasma concentration: a prospective study in 100 de novo renal allograft recipients

Therapeutic Drug Monitoring in Patients with Systemic Lupus Erythematosus: Utility and Gaps

Despite advances in the treatment of patients with systemic lupus erythematous (SLE), outcomes have remained suboptimal. Persistent disease activity, patient comorbidities and drug toxicities contribute to the accrual of progressive irreversible damage and high rates of morbidity and mortality. Currently, similar drug doses and regimens are promulgated in the treatment guidelines for all SLE patients, despite the vast differences in patient and environmental factors that affect the drugs' metabolism and blood concentrations. This causes a disconnect between drug dosing and drug blood concentrations, which can then result in unpredictability in drug toxicities and therapeutic effects. In this review, we discuss commonly used oral immunosuppressive medications in SLE, their pharmacogenomics, and factors affecting their metabolism and blood concentrations. Further, we highlight the role of therapeutic drug monitoring in SLE, which is the first accessible step to individualising therapy.

Clinical Evidence on the Purported Pharmacokinetic Interactions between Corticosteroids and Mycophenolic Acid

Corticosteroids (steroids) are commonly used concurrently with mycophenolic acid (MPA) as the first-line immunosuppression therapy for the prevention of rejection in solid organ transplantations. Steroids are also commonly administered with MPA in various autoimmune disorders such as systemic lupus erythematosus and idiopathic nephrotic syndrome. Despite various review articles having suggested the presence of pharmacokinetic interactions between MPA and steroids, definitive data have not yet been demonstrated. The aim of this Current Opinion is to critically evaluate the available clinical data and propose the optimal study design for characterising the MPA-steroid pharmacokinetic interactions. The PubMed and Embase databases were searched for relevant clinical articles in English as of September 29, 2022, where a total of 8 papers have been identified as supporting and 22 as non-supporting the purported drug interaction. To objectively evaluate the data, novel assessment criteria to effectively diagnose the interaction based on known MPA pharmacology were formulated, including the availability of independent control groups, prednisolone concentrations, MPA metabolite data, unbound MPA concentrations, and the characterisations of entero-hepatic recirculation and MPA renal clearance. Overall, the majority of the identified corticosteroid data were pertaining to prednisone or prednisolone. Our assessment indicated that no conclusive mechanistic data supporting the interaction are available in the current clinical literature, and further studies are required to quantify the effects/mechanisms of steroid-tapering or withdrawal on MPA pharmacokinetics. This current opinion provides justification for further translational investigations, as this particular drug interaction has the potential to exert significant adverse outcomes in patients prescribed MPA.

Pharmacokinetics of free and total mycophenolic acid in paediatric and adult renal transplant recipients: Exploratory analysis of the effects of clinical factors and gene variants

Clinical and genetic influencing factors on free fraction of mycophenolic acid (MPA) have rarely been discussed. The present study investigated whether the clinical and genetic factors could explain the variability in the pharmacokinetics of free MPA (fMPA) and total MPA (tMPA) in Chinese paediatric and adult renal transplant recipients. Twenty-eight paediatric and 31 adult patients were enrolled, and the concentrations of tMPA and fMPA were determined at 0 h (predose) and 0.5, 1, 1.5, 2, 4, 5, 8, 9, 10 and 12 h after mycophenolate mofetil administration. Genetic polymorphisms of UGTs (rs671448, rs1042597, rs2741049, rs62298861, rs7439366, rs12233719) and ABCC2 (rs717620) were simultaneously determined. The clinical and genetic data were analysed and reported. tMPA and fMPA concentrations adjusted for dose per body weight were consistently higher in adults than in paediatric patients. In the paediatric group, only albumin and time after transplantation correlated significantly with the MPA-free fraction variation, which could explain 32.4% of the variability. Besides, ABCC2 polymorphism, albumin and time after transplantation correlated significantly with the MPA-free fraction variation in adults, which could explain 56.9% of the variability. The influencing factors in the paediatric group are different from those in adults, which may be due to age-related transporter expression.

Effects of Corticosteroid Treatment on Mycophenolic Acid Exposure in Renal Transplant Patients-Results From the SAILOR Study

Background: Mycophenolic acid (MPA) is a potent immunosuppressive agent used in solid organ transplantation. MPA exhibits large interindividual variation in dose-normalized plasma concentrations but is nevertheless usually prescribed as a fixed dose without use of therapeutic drug monitoring (TDM). Data on the effect of corticosteroid (CS) treatment on MPA concentrations during concomitant tacrolimus treatment remains sparse. Methods: Data is based on TDM of MPA area under the concentration curve (AUC) in 210 renal transplant recipients participating in the prospective, randomized, controlled, multi-center trial (SAILOR) where a steroid-free immunosuppressive regimen with mycophenolate mofetil (MMF) and low-dose tacrolimus was compared with a conventional prednisolone-based treatment regimen. Multilevel mixed-effects linear regression post-hoc analyses of MPA AUC was performed. Results: Median MPA AUC at baseline (within the first 2 weeks post-transplant) in patients taking 2 g MMF daily was 53 mg*h/L (interquartile range: 43-69 mg*h/L, min: 24-max: 117 mg*h/L). Between-patient variation in MPA AUC was up to 5-fold on the same MMF dose. Patients in the steroid-free group had 12.5% lower (95% CI; 3.2-20.9%, p = 0.01) MPA AUC levels at baseline compared to the steroid treated group. During follow-up (14 days-2 years post-transplant) there were no significant differences in MPA AUC between the groups with MPA AUC being 4.2% lower (95% CI: -4.8%-12,5%, p = 0.35) in the steroid-free vs standard treatment group in restricted analysis after multivariate adjustment for tacrolimus trough level, body weight, time after transplantation and MMF dose. MMF dose was positively correlated with MPA AUC (p < 0.001) whereas body weight was negatively correlated with MPA AUC (p < 0.001). MPA AUC was 0.4% (95% CI: 0.2-0.6%, p < 0.001) lower per 1 kg increase in weight. Tacrolimus trough levels had no significant effect on MPA AUC. Conclusion: Immunosuppression with CS during concomitant tacrolimus treatment was shortly after transplantation associated with a significantly higher MPA exposure but the effect was small and not maintained during follow-up. Low body weight was associated with higher MPA exposure, which suggests a potential for weight adjusted MMF dosing.

Effect of UGT polymorphisms on pharmacokinetics and adverse reactions of mycophenolic acid in kidney transplant patients

Mycophenolic acid (MPA) is a common immunosuppressive drug for kidney transplantation patients, and is characterized by a narrow therapeutic index and significant individual variability. UGTs are the main enzymes responsible for the metabolism of MPA. Although, many studies have focused on the relationship between UGT polymorphisms and pharmacokinetics and adverse reactions of MPA, the conclusion are controversial. We reviewed the relevant literature and summarized the significant influences of UGT polymorphisms, such as UGT1A8 (rs1042597, rs17863762), UGT1A9 (rs72551330, rs6714486, rs17868320, rs2741045, rs2741045) and UGT2B7 (rs7438135, rs7439366, rs7662029), on the pharmacokinetics of MPA and its metabolites and adverse reactions. The review provides a reference for guiding the individualized administration of MPA and reducing adverse reactions to MPA.

A new lateral flow assay to detect sIL-2R during T-cell mediated rejection after kidney transplantation

Kidney is the most frequently transplanted among all solid organs worldwide. Kidney transplant recipients (KTRs) undergo regular follow-up examinations for the early detection of acute rejections. The gold standard for proving a T-cell mediated rejection (TCMR) is a biopsy of the renal graft often occurring as indication biopsy, in parallel to an increased serum creatinine that may indicate deterioration of renal transplant function. The goal of the current work was to establish a lateral flow assay (LFA) for diagnosing acute TCMR to avoid harmful, invasive biopsies. Soluble interleukin-2 (IL-2) receptor (sIl-2R) is a potential biomarker representing the α-subunit of the IL-2 receptor produced by activated T-cells, e.g., after allogen contact. To explore the diagnostic potential of sIL-2R as a biomarker for TCMR and borderline TCMR, plasma and urine samples were collected from three independent KTR cohorts with various distinct histopathological diagnostic findings according to BANFF (containing 112 rsp. 71 rsp. 61 KTRs). Samples were analyzed by a Luminex-based multiplex technique and cut off-ranges were determined. An LFA was established with two specific sIL-2R-antibodies immobilized on a nitrocellulose membrane. A significant association between TCMR, borderline TCMR and sIL-2R in plasma and between TCMR and sIL-2R in urine of KTRs was confirmed using the Mann-Whitney U test. The LFA was tested with sIL-2R-spiked buffer samples establishing a detection limit of 25 pM. The performance of the new LFA was confirmed by analyzing urine samples of the 2^nd and 3^rd patient cohort with 35 KTRs with biopsy proven TCMRs, 3 KTRs diagnosed with borderline TCMR, 1 mixed AMR/TCMR rsp. AMR/borderline TCMR and 13 control patients with a rejection-free kidney graft proven by protocol biopsies. The new point-of-care assay showed a specificity of 84.6% and sensitivity of 87.5%, and a superior estimated glomerular filtration rate (eGFR) at the time point of biopsy (specificity 30.8%, sensitivity 85%).

Initial mycophenolate dose in tacrolimus treated renal transplant recipients, a cohort study comparing leukopaenia, rejection and long-term graft function

The evidence supporting an initial mycophenolate mofetil (MMF) dose of 2 g daily in tacrolimus-treated renal transplant recipients is limited. In a non-contemporaneous single-centre cohort study we compared the incidence of leukopaenia, rejection and graft dysfunction in patients initiated on MMF 1.5 g and 2 g daily. Baseline characteristics and tacrolimus trough levels were similar by MMF group. MMF doses became equivalent between groups by 12-months post-transplant, driven by dose reductions in the 2 g group. Leukopaenia occurred in 42.4% of patients by 12-months post-transplant. MMF 2 g was associated with a 1.80-fold increased risk of leukopaenia compared to 1.5 g. Rejection occurred in 44.8% of patients by 12-months post-transplantation. MMF 2 g was associated with half the risk of rejection relative to MMF 1.5 g. Over the first 7-years post-transplantation there was no difference in renal function between groups. Additionally, the development of leukopaenia or rejection did not result in reduced renal function at 7-years post-transplant. Leukopaenia was not associated with an increased incidence of serious infections or rejection. This study demonstrates the initial MMF dose has implications for the incidence of leukopaenia and rejection. Since neither dose produced superior long-term graft function, clinical equipoise remains regarding the optimal initial mycophenolate dose in tacrolimus-treated renal transplant recipients.

Pharmacokinetic evaluation of MFF in combinations with tacrolimus and cyclosporine. Findings of C0 and AUC

We hypothesized that area under the concentration time curve (AUC(0-12)) is more accurate pharmacokinetic predictor vs trough level of mycophenolic acid (C0).Study was performed at the University Hospital of Limoges (France) and included 238 renal recipients aged 22 to 82 years. Risk of nephropathy was evaluated by analyzing data of protocol biopsies according to the Banff 97 classification.Assessment of immunosuppressants' exposures was based on the calculation of the mean of AUC(0-12). The AUC(0-12) was estimated using a Bayesian estimator and a 3-point limited sampling strategy. Cyclosporine and tacrolimus analyses were performed using liquid chromatography-mass spectrometry method. The measurement of total mycophenolic acid was performed using a validated high-performance liquid chromatography method with ultraviolet detection. IBM SPSS 20.0 was used for statistical analysis.The most accurate dosing of mycophenolate mofetil (MMF) was observed in patients receiving MMF with tacrolimus, 70.6% of patients' AUC(0-12) exposures were within the therapeutic range. The highest rates of low dosing were observed in patients receiving MMF with cyclosporine, 30.9% of patients had AUC(0-12) exposures below the therapeutic range. The assessment of AUC(0-12) revealed 38% of chronic nephropathy cases, while C0 enables to identify only 20% of chronic nephropathy cases.Probability test results showed that more likely AUC(0-12) and C0 will be maintained within the therapeutic width if patients receive MMF with tacrolimus vs MMF with cyclosporine: 0.6320 vs 0.6410 for AUC(0-12) determination and 0.8415 vs 0.4827 for C0 determination.Combination of MMF with tacrolimus is dosed more precisely vs dosing of MMF with cyclosporine. 72 (70.6%) patients AUC(0-12) and 79 (77.5%) patients C0 out of 102 patients were within the therapeutic range. The AUC(0-12) monitoring of mycophenolic acid in patients receiving MMF with tacrolimus or in patients receiving MMF with cyclosporine enabled to identify more overdosing and possible risky cases.Study results show that standard MMF dosing without monitoring and with mycophenolic acid level within the therapeutic width is possible and demonstrates less risky cases in patients receiving MMF with tacrolimus, while patients receiving MMF with cyclosporine should be intensively monitored to achieve the highest safety. However, AUC(0-12) monitoring is advised showing better compliance vs C0 monitoring.

Optimizing Mycophenolic Acid Exposure in Kidney Transplant Recipients: Time for Target Concentration Intervention

The immunosuppressive agent mycophenolate is used extensively in kidney transplantation, yet dosing strategy applied varies markedly from fixed dosing ("one-dose-fits-all"), to mycophenolic acid (MPA) trough concentration monitoring, to dose optimization to an MPA exposure target (as area under the concentration-time curve [MPA AUC0-12]). This relates in part to inconsistent results in prospective trials of concentration-controlled dosing (CCD). In this review, the totality of evidence supporting mycophenolate CCD is examined: pharmacological characteristics, observational data linking exposure to efficacy and toxicities, and randomized controlled trials of CCD, with attention to dose optimization method and exposure achieved. Fixed dosing of mycophenolate consistently leads to underexposure associated with rejection, as well as overexposure associated with toxicities. When CCD is driven by pharmacokinetic calculation to a target concentration (target concentration intervention), MPA exposure is successfully controlled and clinical benefits are seen. There remains a need for consensus on practical aspects of mycophenolate target concentration intervention in contemporary tacrolimus-containing regimens and future research to define maintenance phase exposure targets. However, given ongoing consequences of both overimmunosuppression and underimmunosuppression in kidney transplantation, impacting short- and long-term outcomes, these should be a priority. The imprecise "one-dose-fits-all" approach should be replaced by the clinically proven MPA target concentration strategy.

Early pharmacokinetics of low dosage mycophenolate exposure in Thai kidney transplant recipients

Background The effects of mycophenolic acid exposure in the early period after transplantation on clinical outcomes have been reported; however, mycophenolic acid exposure in the early period after transplantation in Asian kidney transplant recipients who receive 1.5 g/d mycophenolate mofetil has never been investigated. Objective To determine mycophenolic acid exposure on day 3 post-transplantation in kidney transplant recipiens who receive 1.5 g/d mycophenolate mofetil. The effects of the reduced renal function on mycophenolic acid area under the concentration-time curve (AUC) and the achievement of the target AUC on the incidence of biopsy proven acute rejection during the first month post-transplantation were also evaluated. Setting A university hospital Method Blood samples and 24-h urine were collected on day 3 post-transplantation. Main outcome measures The mycophenolic acid AUC was calculated by linear trapezoidal rule and compared with the target of 45 mg*h/L. Results Of 42 Thai kidney transplant recipiens, the mean mycophenolic acid AUC of 45.1 mg*h/L (SD 14.7) was comparable to the AUC target (P = 0.962). Significant differences of the mycophenolic acid AUC were observed between patients with urine output of < 2400 mL and those with urine output ≥ 2400 mL (35.3 ± 6.6 and 47.4 ± 15.2, respectively; P = 0.002), and between patients with 24-h measured CrCl < 25 mL/min and those with CrCl ≥ 25 mL/min (38.0 (29.0, 42.2) and 49.2 ± 14.0, respectively; P = 0.017). Proportions of overall biopsy proven acute rejection among patients with mycophenolic acid AUC of < 45 and ≥ 45 mg*h/L were comparable (20.0% and 23.5%, respectively; P = 1.000). Conclusions After the starting dosage of 1.5 g/d mycophenolate mofetil, the mean mycophenolic acid AUC on day 3 post-kidney transplantation is comparable with the target of 45 mg*h/L. Severely reduced renal function significantly influences mycophenolic acid exposure.

Clinical Implication of Mycophenolic Acid Trough Concentration Monitoring in Kidney Transplant Patients on a Tacrolimus Triple Maintenance Regimen: A Single-Center Experience

Background

This study was designed to analyze the clinical implications of mycophenolic acid trough concentration monitoring.

Material/Methods

We collected data of patients with mycophenolic acid trough concentration monitoring after their first kidney transplant between November 2006 and March 2015 who were prescribed tacrolimus, mycophenolate, and methylprednisolone. Analyses were performed on 3 periods: 1 month, 1 month to 1 year, and after 1 year post-transplantation. To analyze factors related to acute cellular rejection, logistic regression was used for 1 month, while Cox analysis was used during 1 month to 1 year and after 1 year post-transplantation.

Results

In the 145 patients receiving mycophenolate mofetil, mean tacrolimus trough ≥7.0 ng/mL (OR=0.177, CI=0.060–0.524, p=0.002) and mean mycophenolic acid trough ≥1.7 mg/L (OR=0.190, CI=0.040–0.896, p=0.036) were protective for rejection during 1 month. Mean mycophenolic acid trough ≥1.7 mg/L (HR=0.179, CI=0.040–0.806, p=0.025) and ≥0.7 mg/L (HR=0.142, CI=0.028–0.729, p=0.019) were related to better rejection-free survival during 1 month to 1 year and after 1 year, respectively. In 399 patients receiving enteric-coated mycophenolate sodium, mean tacrolimus trough ≥7.0 ng/mL (OR=0.258, CI=0.131–0.507, p<0.001) and mean mycophenolic acid trough ≥2.1 mg/L (OR=0.507, CI=0.264–0.973, p=0.041) were protective for rejection during 1 month. Mean mycophenolic acid trough ≥1.7 mg/L (HR=0.519, CI=0.289–0.932, p=0.028) and ≥0.7 mg/L (HR=0.208, CI=0.072–0.602, p=0.004) were related to better rejection-free survival during 1 month to 1 year and after 1 year, respectively.

Conclusions

Mycophenolic acid trough concentration monitoring can be useful in preventing acute cellular rejection in patients receiving tacrolimus, mycophenolate, and methylprednisolone.

Pharmacokinetic Variability of Mycophenolic Acid in Pediatric and Adult Patients With Hematopoietic Stem Cell Transplantation

The aim of this study was to evaluate the pharmacokinetic variations of mycophenolic acid (MPA), the active metabolite of mycophenolate mofetil (MMF), in both pediatric and adult patients following hematopoietic stem cell transplantation (HSCT). Twenty pediatric patients with a median age of 3 years (range 0.2-12 years) and 13 adult patients with a median age of 54 years (range 18-63 years) were enrolled. Blood samples were collected on days 0, 7, 14, 21, and 30 after allogeneic HSCT. Total and free (unbound) MPA as well as MPA 7-O-glucuronide (MPAG) were quantified using a validated LC-MS/MS assay. The plasma protein binding of MPA and MPAG did not change significantly in pediatric patients over the 1-month sampling period post-HSCT. However, it increased in adult patients from day 7 to day 30 post-HSCT, from 97.3 ± 0.8% to 98.3 ± 0.6% for MPA (P < .05), and 74.6 ± 9.4% to 82.9 ± 8.1% for MPAG (P < .05). The plasma protein binding of MPA was significantly higher in males compared to females in both pediatric (98.3 ± 1.1% vs 97.4 ± 1.1%) and adult (98.1 ± 0.7% vs 97.4 ± 1.2%) patients (P < .05). The MPAG/MPA ratios on a milligram-per-kilogram dose basis in adult patients were significantly higher than those in pediatric patients (4.3 ± 3.4 vs 2.4 ± 2.6; P < .05). Time-dependent plasma protein binding and age-related differences in MPA metabolism at least in part impact the reported large intra- and interindividual variability in MPA pharmacokinetics. These patient and pharmacologic factors, if incorporated into MMF regimen design and modification, may contribute to the rational dose selection of MMF in HSCT patients.

Tacrolimus and mycophenolate regimen and subclinical tubulo-interstitial inflammation in low immunological risk renal transplants

The aim was to evaluate the relationship between maintenance immunosuppression, subclinical tubulo-interstitial inflammation and interstitial fibrosis/tubular atrophy (IF/TA) in surveillance biopsies performed in low immunological risk renal transplants at two transplant centers. The Barcelona cohort consisted of 109 early and 66 late biopsies in patients receiving high tacrolimus (TAC-C₀ target at 1-year 6-10 ng/ml) and reduced MMF dose (500 mg bid at 1-year). The Oslo cohort consisted of 262 early and 237 late biopsies performed in patients treated with low TAC-C₀ (target 3-7 ng/ml) and standard MMF dose (750 mg bid). Subclinical inflammation, adjusted for confounders, was associated with low TAC-C₀ in the early (OR: 0.75, 95% CI: 0.61-0.92; P = 0.006) and late biopsies (OR: 0.69, 95% CI: 0.50-0.95; P = 0.023) from Barcelona. In the Oslo cohort, it was associated with low MMF in early biopsies (OR: 0.90, 95% CI: 0.83-0.98; P = 0.0101) and with low TAC-C₀ in late biopsies (OR: 0.77, 95% CI: 0.61-0.97; P = 0.0286). MMF dose was significantly reduced in Oslo between early and late biopsies. IF/TA was not associated with TAC-C₀ or MMF dose in the multivariate analysis. Our data suggest that in TAC- and MMF-based regimens, TAC-C₀ levels are associated with subclinical inflammation in patients receiving reduced MMF dose.

Pharmacokinetics of Mycophenolic Acid and Its Glucuronidated Metabolites in Stable Lung Transplant Recipients

Background:

Mycophenolic acid (MPA) is the active metabolite of mycophenolate mofetil, an immunosuppressive agent commonly used in solid organ transplantation. MPA is metabolized to the inactive metabolite 7-O-mycophenolic acid glucuronide (MPAG) and the active metabolite acyl glucuronide (AcMPAG). Pharmacokinetic profiling of MPA by determining AUC is a tool for determining drug exposure. Many studies, conducted primarily in kidney and some heart and liver transplant recipients, have shown wide interpatient variability in MPA's pharmacokinetic parameters. There have been few studies in the lung transplant group and, even though the lung is not involved in drug elimination, these patients may have different MPA pharmacokinetic characteristics.

Objective:

To characterize the pharmacokinetic parameters and metabolic ratios of MPA in stable adult lung transplant recipients.

Methods:

In an open-label manner, lung transplant recipients were recruited. Blood samples were obtained at 0, 0.3, 0.6, 1, 1.5, 2, 4, 6, 8, 10, and 12 hours postdose. Plasma was separated and acidified for drug concentration analysis (MPA, MPAG, AcMPAG) by an HPLC–ultraviolet detection method. Conventional pharmacokinetic parameters were determined via noncompartmental methods.

Results:

There was large interpatient variability in all pharmacokinetic parameters of MPA, MPAG, and AcMPAG. Similar variability was observed after stratifying patients into concomitant medication groups: cyclosporine and tacrolimus. There was a trend for the tacrolimus group to have a higher dose-normalized AUC, higher AUC, lower apparent clearance, and lower AUC ratio of AcMPAG/MPA compared with the cyclosporine group. In addition, the cyclosporine group had a lower minimum concentration and higher AUC ratio of MPAG/MPA than did the tacrolimus group (p < 0.05).

Conclusions:

Because of the large interpatient variability in the pharmacokinetic parameters of MPA, MPAG, and AcMPAG, therapeutic drug monitoring of MPA and its metabolites in lung transplant recipients may be beneficial.

Pharmacokinetics of mycophenolic acid in children with clinically stable idiopathic nephrotic syndrome receiving cyclosporine

BACKGROUND

The suitable dosage regime of mycophenolate mofetil (MMF) based on the pharmacokinetics of mycophenoric acid (MPA) for pediatric patients with idiopathic nephrotic syndrome (INS) is controversial. The pharmacokinetics of MPA is influenced by renal function, serum albumin concentration, and concomitant medications, especially calcineurin inhibitors. This study analyzed the pharmacokinetics of MPA in clinically stable children with INS receiving cyclosporine (CyA).

METHODS

This retrospective study enrolled children with INS receiving MMF (Cellcept^®) (30-40 mg/kg/day in two divided doses) combined with CyA (Neoral^®) without relapse and renal dysfunction. Pharmacokinetic parameters, including the area under the concentration-time curve (AUC) calculated by the trapezoid method, were calculated from seven serial blood samples.

RESULTS

Thirty-two patients (22 males) of median age 11.0 years were included; 32 pharmacokinetic studies were performed. The median MMF dose was 16.2 mg/kg/time or 470.4 mg/m²/time. The median AUC0-12 was 44.3 ng h/mL. AUC0-12 of all patients showed excellent correlations with C2 (r ²  = 0.6405, P < 0.0001), resulting in a regression formula of AUC0-12 = 21.971 + 2.6059 C2. Comparisons of dose/body weight-normalized AUC0-12 values among age groups showed a lower value in the youngest group (≤5 years).

CONCLUSION

In children with clinically stable INS receiving CyA, C2 monitoring was the most useful single parameter for estimating MPA pharmacokinetics. Younger children required higher MMF doses.

The Value of Monitoring the Serum Concentration of Mycophenolate Mofetil in Children with Steroid-Dependent/Frequent Relapsing Nephrotic Syndrome

BACKGROUND

Mycophenolate mofetil (MMF) is an alternative treatment strategy in children with steroid sensitivity who have frequent relapses or steroid-dependent nephrotic syndrome (FRNS/SDNS).

METHODS

From January 2009 to January 2015, 31 cases of children with FRNS/SDNS were prospectively recruited and administered MMF and prednisone; then, serum samples were collected, and the area under the curve (AUC) of mycophenolic acid (MPA-AUC) was calculated.

RESULTS

A MPA-AUC of 27.99 μg·h/ml had a diagnostic sensitivity of 65.2% and a specificity of 87.5% in discriminating relapsing from non-relapsing patients (receiver operating characteristic-AUC 0.848). The 31 patients were then grouped according to the results of the MPA-AUC as follows: low-AUC group, <30 μg·h/ml and high-AUC group, ≥30 μg·h/ml. The results indicated that there was a significant difference in the remission rate between the groups (x03C7;2 = 6.645, p = 0.01) during the 6 months of follow-up. Compared with the results before MMF therapy, the steroid dosage in both groups was significantly reduced at the 6- and 12-month follow-ups. Furthermore, the steroid dose was reduced more significantly in the high-AUC group than in the low-AUC group (0.447 ± 0.254 vs. 0.219 ± 0.161 mg/kg/day, p = 0.006) at the 6-month follow-up. Compared with the low-AUC group at the 6-month follow-up, the number of patients with relapse and relapse episodes in the high-AUC group were also significantly reduced (7/16 vs. 1/15, p = 0.037, and 15/27 vs. 1/29, p = 0.014, respectively).

CONCLUSIONS

MMF is a reasonable treatment choice to reduce the number of relapse episodes and steroid administration in children with FRNS/SDNS. Moreover, children in the high-AUC group (MPA-AUC ≥30 μg·h/ml) tended to require lower steroid doses and had greater remission rates than the patients in the low-AUC group (<30 μg·h/ml) at the 6-month follow-up.

Implications of Clinical Mycophenolate Mofetil Dose According to Individual Body Weight in Japanese Renal Transplant Recipients

BACKGROUND

Mycophenolate mofetil (MMF) is generally administered at a fixed dose of 0.5-1.5 g/d without considering individual body weight (BW) in Japanese renal transplant outpatients receiving maintenance therapy. We aimed to investigate the implications of the area under the curve of mycophenolic acid (MPA AUC):MMF dose ratio by individual BW and suggest the index of MMF dose according to individual BW.

METHODS

Forty-three Japanese patients who received a renal transplant ≥6 months before the study were enrolled. Blood samples were collected at 4 time points: at predose, 20 minutes, 1 hour, and 3 hours after MMF administration.

RESULTS

The mean ± standard deviation MMF dose, MPA AUC, and BW of all patients were 581 ± 207 mg/d, 36.2 ± 18.7 μg·h/mL, and 56.3 ± 11.1 kg, respectively. Patients with a lower BW tended to have a higher MPA AUC:MMF dose ratio than patients with a higher BW. There was a significant correlation between the MMF dose:BW ratios and MPA AUC (r(2) = 0.330; P < .01). The rate of MPA AUC between 30 and 60 μg·h/mL with the MMF dose:BW ratio of 10-16 mg/kg was 73.7%.

CONCLUSION

Individual BW seems to affect the MPA AUC:MMF dose ratio; therefore, we need to consider individual BW when deciding on a MMF dose. The MMF dose:BW ratio of 10-16 mg/kg could predict MPA AUC between 30 and 60 μg·h/mL with a probability of approximately 75%. Therefore, it could be a useful index for outpatients, because it is difficult to draw blood frequently from such patients.

Use of Glucuronidated Mycophenolic Acid Levels for Therapeutic Monitoring in Pediatric Lupus Nephritis Patients

BACKGROUND/OBJECTIVES

Mycophenolate mofetil (MMF) is used to treat pediatric-onset lupus nephritis (pLN). Data are equivocal on the use of plasma mycophenolic acid (MPA) levels as a measure of efficacy and predictor of therapeutic outcomes in pLN. Glucuronidated MPA (MPA-G) is an inactive metabolite that is a marker of adequate absorption and normal metabolism of MMF. We evaluated the use of MPA and MPA-G levels in routine care of pLN.

METHODS

This was a retrospective study of pLN patients treated with MMF dosed at 600 mg/m. Clinical renal remission (CR) was defined as proteinuria of less than 500 mg/24 h. Midinterval MPA and MPA-G plasma levels were drawn during routine follow-up, approximately 6 hours after the previous dose of MMF. Steady-state levels of MPA were calculated using pharmacokinetics and compared with routine midinterval plasma MPA levels.

RESULTS

Seventeen pLN patients treated with MMF had MPA and MPA-G levels. Eleven patients were in CR; 6 were not in CR at the time of evaluation and had not responded to MMF after more than 3 months of therapy. The mean MPA level for patients in CR was 3.26 ± 2.02 μg/mL compared with 3.02 ± 1.76 μg/mL for patients not in CR. Three patients in CR did not have detectable levels of MPA. Calculated steady-state levels of MPA did not reflect the observed levels. Glucuronidated MPA levels were therapeutic (44.2 ± 26.7 μg/mL) in patients in CR, but low (29.88 ± 22 μg/mL) in patients not in CR (not statistically significant).

CONCLUSIONS

Midinterval plasma levels of MPA do not reflect predicted steady-state levels in pLN and do not correlate with clinical response. Midinterval plasma levels of MPA-G indicate adequate absorption and may correlate better with clinical pLN activity.

Pharmacokinetics of mycophenolate mofetil in Omani patients on cyclosporine or tacrolimus

BACKGROUND

Mycophenolate mofetil (MMF) reduces rejection in organ transplantation and is effective in controlling autoimmune diseases. Determining the area under the receiver operating characteristic curve (AUC) of MMF is not routine despite interindividual variability. The aim of this study was to look into MMF-AUC in Omani patients on cyclosporine (CsA) or tacrolimus (Tac).

METHODS

We measured MMF-AUC in 27 stable Omani patients. We used the 4-time-points-limited sampling strategy.

RESULTS

Sixteen, 8, and 3 recipients were receiving Tac, CsA, and calcineurin inhibitor (CNI)-free regimens, respectively. The mean MMF dose was 1,685 ± 442 mg/d. All except 3 patients were within or above the target AUC. The AUC was significantly higher in patients receiving Tac versus CsA. All patients on Tac were within or above the target AUC. Seven of the 8 patients with MMF-AUC above target were receiving Tac. Two of the 3 patients with MMF-AUC below target were on CsA.

DISCUSSION

These preliminary results confirm the significant interindividual variability of MMF-AUC. None of the recipients on Tac had an AUC below target. Most patients above the target AUC were receiving Tac. Two of the 3 patients with MMF-AUC below target were on CsA and receiving 1 g/d MMF. Patients on Tac are at risk of having higher than the target AUC, exposing them to overimmunosuppression. Recipients on CsA seem to require >1 g/d MMF.

CONCLUSIONS

These preliminary results encourage measuring the AUC of MMF. The fixed MMF dose regimen seems to be unreliable to predict the AUC. Preventing under- or overimmunosuppression offsets the burden.

Spectroscopy study and co-administration effect on the interaction of mycophenolic acid and human serum albumin

Mycophenolic acid (MPA), an immunosuppressor, is always administered in combination with several drugs in clinical therapy, which may alter the binding of MPA to human serum albumin (HSA) and could influence its pharmacological activities. Thus, this study evaluated the interaction between HSA and MPA, as well as investigated the effect of co-administrated drugs on the MPA-protein binary system using fluorescence spectroscopy. Results revealed that MPA has a strong capability to quench the fluorescence of HSA, and the acting forces for the binding are hydrogen bonds and van der Waals forces. Competition on combined administration showed that balofloxacin significantly affects the MPA-HSA interaction, as reflected by the remarkable decrease in fluorescence intensity. Furthermore, cefminox sodium has competitive capability with MPA to some extent, whereas methyl prednisone and amlodipine besylate have a minor influence on the binary system. However, simvastatin has no appreciable effect on the MPA-HSA interaction. In addition, three-dimensional fluorescence spectra and circular dichroism spectroscopy, which were employed to determine the conformation, showed that the binding of MPA with HSA can induce conformation changes in HSA.

Mycophenolic acid AUC in Thai kidney transplant recipients receiving low dose mycophenolate and its association with UGT2B7 polymorphisms

Background

Despite use of a lower mycophenolate dose in Thai kidney transplant patients, acceptable graft and patient outcomes can be achieved. We therefore examined the pharmacokinetics of mycophenolic acid (MPA) by area under the curve (AUC) and investigated genetic contribution in mycophenolate metabolism in this population.

Methods

Kidney transplant recipients with stable graft function who were receiving mycophenolate mofetil 1,000 mg/d in combination with either cyclosporine or tacrolimus, and prednisolone were studied. The MPA concentration was measured by fluorescence polarization immunoassay (FPIA), at predose and 1, 1.5, 2, 4, 6, 8, 10, and 12 hours after dosing. Genetic polymorphisms in UGT1A8, UGT1A9, and UGT2B7 were examined by denaturing high-performance liquid chromatography (DHPLC)-based single-base extension (SBE) analysis.

Results

A total 138 patients were included in study. The mean AUC was 39.49 mg-h/L (28.39–89.58 mg-h/L), which was in the therapeutic range. The correlation between the predose MPA concentration and AUC was poor. The mean AUC in the tacrolimus group was higher than that in the cyclosporine group. Polymorphisms in UGT2B7 showed significant association with AUC.

Conclusion

Most of our patients with reduced mycophenolate dose had the AUC within the therapeutic range. Genetic polymorphisms in UGT2B7 may play a role in MPA metabolism in Thai kidney transplant patients.

Development and validation of limited sampling strategies for the estimation of mycophenolic acid area under the curve in adult kidney and liver transplant recipients receiving concomitant enteric-coated mycophenolate sodium and tacrolimus

BACKGROUND

Mycophenolic acid (MPA) is widely used in solid organ transplantation. MPA absorption from enteric-coated mycophenolate sodium (EC-MPS) is delayed, which results in a delayed enterohepatic recirculation and subsequently higher and more variable MPA 12-hour trough concentration and tmax values. Therefore, MPA trough level monitoring cannot be used to monitor MPA exposure in patients who are given EC-MPS. The aim of the study was to develop and validate a limited sampling strategy (LSS) for accurate prediction of the 12-hour area under the concentration-time curve (AUC0-12h) for MPA in patients who receive concomitant EC-MPS and Tacrolimus (Prograf or Advagraf) within 196 months posttransplantation. According to our knowledge, the LSS for MPA AUC estimation using high-performance liquid chromatography to determine MPA concentrations in plasma samples of kidney and liver transplant patients receiving EC-MPS and Tacrolimus (Advagraf) has not been previously evaluated.

METHODS

Seventy-four renal and liver transplant patients receiving EC-MPS and concomitant tacrolimus (either Prograf or Advagraf) provided a total of 74 pharmacokinetic profiles. MPA concentrations were measured using a validated high-performance liquid chromatography method for 9 plasma samples collected at predose and at 0.5, 1, 2, 3, 4, 6, 9, and 12 hours after the morning dose of EC-MPS after an overnight fast. LSS were developed and validated by stepwise multiple regression analysis with the use of a 2-group method (test, n = 37; and validation, n = 37).

RESULTS

The 3 and 4 time point equations using C1h, C3h, C9h and C1h, C2h, C3h, C6h, respectively, were found to be superior to all other models tested. When these LSS models were tested in the validation group, the results were acceptable [for 3 time points equation: r = 0.824, percentage of prediction error: 6.32 ± 25.75, 95% confidence interval (CI): -40.71 to 79.76; percentage of absolute prediction error: 27.45 ± 29.89, 95% CI: 0.04-199.92, predictive performance, 71% of estimated AUCs comprised within 85%-115% of the measured full MPA AUC, natural logarithmic residuals (ln) mean ± SD: -0.03 ± 0.24; for 4 time points equation: r = 0.898, percentage of prediction error: 3.32 ± 18.26, 95% CI: -49.35 to 51.06; percentage of absolute prediction error: 14.05 ± 11.89, 95% CI 0.13-49.86, percentage of predictive performance, 83% of estimated AUCs comprised within 85%-115% of the measured full MPA AUC, natural logarithmic residuals (ln) mean ± SD: -0.01 ± 0.19].

CONCLUSIONS

LSS equations using concentrations at 1, 3, and 9 hours or 1, 2, 3, and 6 hours time points provided the most reliable and accurate estimations of the MPA AUC in stable renal and liver transplant recipients treated with EC-MPS and tacrolimus. Further studies on independent groups of patients are required to confirm clinical utility of the presented LSS models.

Maximum a posteriori Bayesian estimation of mycophenolic Acid area under the concentration-time curve: is this clinically useful for dosage prediction yet?

This review seeks to summarize the available data about Bayesian estimation of area under the plasma concentration-time curve (AUC) and dosage prediction for mycophenolic acid (MPA) and evaluate whether sufficient evidence is available for routine use of Bayesian dosage prediction in clinical practice. A literature search identified 14 studies that assessed the predictive performance of maximum a posteriori Bayesian estimation of MPA AUC and one report that retrospectively evaluated how closely dosage recommendations based on Bayesian forecasting achieved targeted MPA exposure. Studies to date have mostly been undertaken in renal transplant recipients, with limited investigation in patients treated with MPA for autoimmune disease or haematopoietic stem cell transplantation. All of these studies have involved use of the mycophenolate mofetil (MMF) formulation of MPA, rather than the enteric-coated mycophenolate sodium (EC-MPS) formulation. Bias associated with estimation of MPA AUC using Bayesian forecasting was generally less than 10%. However some difficulties with imprecision was evident, with values ranging from 4% to 34% (based on estimation involving two or more concentration measurements). Evaluation of whether MPA dosing decisions based on Bayesian forecasting (by the free website service https://pharmaco.chu-limoges.fr) achieved target drug exposure has only been undertaken once. When MMF dosage recommendations were applied by clinicians, a higher proportion (72-80%) of subsequent estimated MPA AUC values were within the 30-60 mg · h/L target range, compared with when dosage recommendations were not followed (only 39-57% within target range). Such findings provide evidence that Bayesian dosage prediction is clinically useful for achieving target MPA AUC. This study, however, was retrospective and focussed only on adult renal transplant recipients. Furthermore, in this study, Bayesian-generated AUC estimations and dosage predictions were not compared with a later full measured AUC but rather with a further AUC estimate based on a second Bayesian analysis. This study also provided some evidence that a useful monitoring schedule for MPA AUC following adult renal transplant would be every 2 weeks during the first month post-transplant, every 1-3 months between months 1 and 12, and each year thereafter. It will be interesting to see further validations in different patient groups using the free website service. In summary, the predictive performance of Bayesian estimation of MPA, comparing estimated with measured AUC values, has been reported in several studies. However, the next step of predicting dosages based on these Bayesian-estimated AUCs, and prospectively determining how closely these predicted dosages give drug exposure matching targeted AUCs, remains largely unaddressed. Further prospective studies are required, particularly in non-renal transplant patients and with the EC-MPS formulation. Other important questions remain to be answered, such as: do Bayesian forecasting methods devised to date use the best population pharmacokinetic models or most accurate algorithms; are the methods simple to use for routine clinical practice; do the algorithms actually improve dosage estimations beyond empirical recommendations in all groups that receive MPA therapy; and, importantly, do the dosage predictions, when followed, improve patient health outcomes?

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

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

Development and validation of limited sampling strategies for tacrolimus and mycophenolate in steroid-free renal transplant regimens

PURPOSE

1) To develop and validate limited sampling strategies (LSSs) for tacrolimus (TAC) and mycophenolic acid (MPA) in renal transplant recipients not receiving corticosteroids; and 2) to evaluate predictive performance of published LSSs (for steroid-based regimens) in a steroid-free population.

METHODS

On administration of steady-state morning TAC and mycophenolate mofetil doses, 12-hour serial blood samples from 28 stable renal transplant recipients were collected and measured by validated high-performance liquid chromatography methods and area under the curve (AUC) by trapezoidal rule. TAC LSSs were developed and validated by multiple regression analysis by a two-group method (index n = 18; validation n = 10) and MPA LSSs by the jackknife method (n = 28). Potential LSSs were those with r ≥ .8 (TAC) or r ≥ 0.7 (MPA) and < 3 time points within 2 hours (TAC) or 4 hours (MPA) postdose. Predictive performance was calculated and other published TAC and MPA LSSs tested using preset criteria for bias and precision of within ± 15%.

RESULTS

For TAC, three three-concentration, one two-concentration, and one one-concentration model met preset criteria. The best equations were: TAC AUC = 10.338 + 7.739C0 + 3.589C2 (r = 0.956, bias = -3.4%, precision = 4.7%) and TAC AUC = 29.479 + 5.016C2 (r = 0.862, bias = 3.2%, precision = 9.7%). For MPA, only one model was identified: MPA AUC = 9.328 + 1.311C1 + 1.455C2 + 2.901C4 (r = 0.838, bias = -3.8%, precision = 14.9%). One published TAC (and no MPA) LSS in renal transplant recipients on steroid-based regimens met criteria.

CONCLUSIONS

To the authors' knowledge, these LSSs are the first to be developed and validated in steroid-free renal transplant recipients and can be used to accurately predict TAC and MPA AUCs for steroid-free regimens. Because the commonly used MPA LSS is based on a steroid regimen and not predictive for steroid-free patients, the newly derived MPA LSS is being applied at the authors' institution. Other renal transplant centers may also wish to validate this equation in their own patients.

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

STUDY OBJECTIVE

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

DESIGN

Open-label, cross-sectional study.

SETTING

Transplant clinic in Vancouver, British Columbia, Canada.

PATIENTS

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

MEASUREMENTS AND MAIN RESULTS

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

CONCLUSION

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

Evalutation of mycophenolic acid systemic exposure by limited sampling strategy in kidney transplant recipients receiving enteric-coated mycophenolate sodium (EC-MPS) and cyclosporine

BACKGROUND

Enteric-coated mycophenolate sodium (EC-MPS) and mycophenolate mofetil (MMF) are prodrugs of mycophenolic acid (MPA). Although many patients still receive MMF as an inosine monophosphate dehydrogenase inhibitor, EC-MPS could be considered a reliable alternative to MMF in the immunosuppressive protocols of kidney transplant recipients. MPA shows high pharmacokinetic variability and consequently a 12-h area under the curve (AUC(0-12)) should be used to guide the therapeutic dosage. However, patient compliance and economic costs make MPA AUC(0-12) an unpractical approach. Limited sampling strategies or predictive systemic drug exposure equation models based on limited sampling times are available only for MMF but lack for EC-MPS.

METHODS

The present study enrolled 26 kidney transplant recipients receiving EC-MPS as part of their immunosuppressive therapy. Twenty-six full MPA AUC(0-12) were performed. By using multiple stepwise regression analysis, we obtained several predictive equations of MPA systemic exposure in this group of patients. The value of the selected equations was tested in a subsequently enrolled group of 26 kidney transplant recipients.

RESULTS

The best equations obtained in the first group of patients were the following: 22.906 + 3.880·C(0) + 1.117·C(1) + 7.527·C(8) (r = 0.901) and 35.064 +3.784·C(0) + 1.002·C(1) + 1.192·C(2) (r = 0.846). These equation models showed an optimal agreement between the full AUCs and estimated AUCs by using the validation group of patients.

CONCLUSIONS

Limited sampling strategies are useful for MPA AUC(0-12) estimation in patients receiving EC-MPS and cyclosporine. The choice of one or the other equation model depends on the pharmacokinetic characteristics of the patients, in particular the potential presence of enterohepatic recirculation.

Mycophenolic acid exposure in high- and low-weight renal transplant patients after dosing with mycophenolate mofetil in the Opticept trial

The Opticept trial was an open-label, randomized, multicenter trial involving 720 kidney recipients. Three immunosuppressant dosing regimens were evaluated, including both fixed and concentration-controlled dosing of mycophenolate mofetil in combination with standard and reduced calcineurin inhibitor levels. Mycophenolic acid (MPA) levels were measured, yielding one of the largest databases to assess the impact of variables on MPA exposure. The present subset analysis evaluated the effect of baseline body weight in three noncontiguous weight categories on MPA exposure at steady state (Day 90) in patients receiving tacrolimus. Multivariate linear regression models assessed the relationship between area under the concentration-time curve (AUC) and several variables. In all, 219 patients had baseline weights in the three categories and an MPA AUC at Day 90: 50 kg or less (n = 12, all female); 60 to 80 kg (n = 136); or 100 kg or greater (n = 71). In overall comparisons by weight class, clearance increased with increased weight, resulting in an inverse relationship between dose-corrected MPA AUCs and weight at Day 90 (P < 0.0001). In patients of extreme weight, wide disparities of MPA exposure were measured despite the mean mycophenolate mofetil dose, notably in those 50 kg or less who had comparatively high dose-corrected MPA AUCs. Patients at the extremes of weight might be at risk of over- or underimmunosuppression unless doses are adjusted.

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.

Pharmacokinetics of mycophenolic acid in severe lupus nephritis

Mycophenolic acid (MPA) is an effective treatment for active lupus nephritis despite its variable efficacy in different ethnic groups. Here we tested whether pharmacokinetic monitoring may help to optimize dosing of MPA in an Asian population. Patients with biopsy-proven class III or IV lupus nephritis (ISN/RPS category) were treated with mycophenolate mofetil or enteric-coated mycophenolate sodium. One month after initiating treatment we measured plasma MPA levels in eight samples taken over a 12-h period after drug administration. The mean area under the time-dependent curve for MPA of responding patients was significantly higher than those not responding. Successful treatment was seen in patients with areas >45 mg h/l. The dosage of the drug was not related to MPA pharmacokinetics. In the mycophenolate mofetil group, however, MPA-area under the curve was positively, and significantly, correlated with trough or 1 h after dose concentrations and associated with a therapeutic response. Thus, our study shows that MPA pharmacokinetics were positively correlated with therapeutic responses of mycophenolate, suggesting that controlling the concentrations may improve its therapeutic efficacy in lupus nephritis. As the absorption and pharmacokinetic peak of enteric-coated tablets is slower, it is important to take different formulations into account when determining optimal MPA concentrations.

Immunosuppression armamentarium in 2010: mechanistic and clinical considerations

Effective immunosuppression is the key to successful organ transplantation, with success being defined as minimal rejection risk with concomitant minimal drug toxicities. Despite the general recognition of this fact, a paucity of appropriate clinical trials in children has contributed to lack of standardization of clinical management regimens, resulting in an extensive diversity of favored approaches. Nonetheless, although consensus has not been reached on the ideal approach to immunosuppression in pediatric transplantation, new drug therapies have contributed to a continuing improvement in graft and patient survival. Future clinical research must focus on diminishing the extensive burden of toxicities of these therapeutic agents in children.