Clinical pharmacokinetics of mycophenolate mofetil in Japanese renal transplant recipients: A retrospective cohort study in a single center

Population pharmacokinetics and limited sampling strategy for therapeutic drug monitoring of mycophenolate mofetil in Japanese patients with lupus nephritis

BACKGROUND

Mycophenolate mofetil (MMF), a prodrug of the immunosuppressive agent mycophenolic acid (MPA), is difficult to administer because of the pharmacokinetic complexity of MPA. Although dosage adjustment according to the 12-h area under the concentration-time curve (AUC_0-12) is thought to be desirable, multiple blood samplings for AUC calculation may pose a clinical challenge. A limited sampling strategy (LSS) would provide a solution; however, little is known about MPA pharmacokinetics in lupus nephritis patients, especially in those with Asian backgrounds, or few, if any, LSSs are reported for them.

METHODS

Thirty-four adult Japanese patients receiving MMF for lupus nephritis were examined retrospectively. MPA pharmacokinetics were investigated, and a PPK model was developed using Phoenix® NLME™ software. Single and double blood sampling strategies from Bayesian estimation using the PPK model and from multiple linear regression were compared. Tolerability was also evaluated.

RESULTS

In the pharmacokinetic analysis, renal function and serum albumin had significant effects on dose-normalized AUC_0-12; and serum albumin, concomitant proton pump inhibitor (PPI) and iron/magnesium oxide did on dose-normalized maximum concentration. As a PPK model, a two-compartment model was developed with a transit absorption model and first-order elimination, in which creatinine clearance and serum albumin were covariates for MPA clearance. The double sampling strategy at 1 and 4 h by multiple linear regression showed the best agreement with the observed AUC_0-12 (r² = 0.885). Of the single sampling strategies, the one at 6 h by Bayesian estimation performed best (r² = 0.769). The tolerability evaluation showed that correlations were suggested for gastrointestinal involvement.

CONCLUSIONS

The present study developed the first PPK model of MPA for Japanese lupus nephritis patients. As for LSSs, a double sampling strategy at 1 and 4 h by multiple linear regression would work best; when only a single blood sampling is allowed, a strategy at 6 h by Bayesian estimation using the PPK model developed in this study would be best. The LSSs good enough for clinical use may facilitate safer, more effective, and individualized therapy.

In vitro and in vivo characterization of AS2643361, a novel and highly potent inosine 5'-monophosphate dehydrogenase inhibitor

Inosine 5'-monophosphate (IMP) dehydrogenase is a critical target in solid organ transplantation. To this end, the development of mycophenolate mofetil (MMF) represents a major advance in transplant medicine. Here, we investigated the in vitro and in vivo pharmacological effects of a novel IMP dehydrogenase inhibitor, AS2643361, in several immunological and non-immunological models. The in vitro inhibitory activity of AS2643361 on immune cell and endothelial cell proliferation and on antibody production from lipopolysaccharide-stimulated B cells, was significantly more potent than that of mycophenolic acid, the active form of MMF, despite the similar potency of these compounds on IMP dehydrogenase. In a rat heterotopic cardiac transplant model, monotherapy using orally administered AS2643361 at 10 or 20mg/kg/day prolonged the median graft survival time from 6 to 16 and 19days, respectively. In dinitrophenol-lipopolysaccharide stimulated rats, oral administration of AS2643361 at 2.5, 5 or 10mg/kg/day resulted in suppression of antibody production. In vivo antibody production against alloantigen was also suppressed by AS2643361 treatment at 5 or 10mg/kg/day. Furthermore, treatment with AS2543361 effectively inhibited balloon injury induced-intimal thickening, which is a major cause of late allograft loss. Overall, the in vivo activity of AS2643361 was over two-fold more potent than that of MMF. In addition, gastrointestinal toxicity, considered a dose-limiting factor for MMF, was reduced with AS2643361 treatment. These results suggest AS2643361 has higher potency and less toxicity than MMF, making it a potential candidate for treatment of acute and chronic rejection in transplant medicine.

The occurrence of diarrhea not related to the pharmacokinetics of MPA and its metabolites in liver transplant patients

PURPOSE

Mycophenolate mofetil (MMF) is a pro-drug that is hydrolyzed to release mycophenolic acid (MPA). Subsequently MPA is extensively metabolized to phenyl mycophenolic acid glucuronide (MPAG) and MPA acyl glucuronide (AcMPAG). It was presumed that the closest association is between plasma AcMPAG concentrations and the incidence of diarrhea. This study aimed to investigate the correlation between pharmacokinetics of MPA, MPAG, and AcMPAG and diarrhea in liver transplant recipients on MMF with tacrolimus.

METHODS

Sixty-seven patients receiving liver transplantation were included. The pharmacokinetics of MPA and its metabolites were monitored repeatedly in the early stage (within 2 weeks) and in the late stage after transplant. The plasma concentrations of MPA, MPAG, and AcMPAG were determined by the HPLC method.

RESULTS

Twenty-two patients (32.8%) suffered from episodes of diarrhea. Compared with the data from the early stage, AUC(0-12h) of MPA, MPAG, and AcMPAG increased significantly in both groups in the later stage. AUC(0-12h) of MPA, MPAG, and AcMPAG were not different significantly between the group with diarrhea and the group without diarrhea, either in the early stage or in the late stage (P > 0.05).

CONCLUSION

These results suggest that systemic exposures to MPA and its metabolites are not associated with the incidence of diarrhea in liver transplant recipients.

Effect of the inosine 5'-monophosphate dehydrogenase inhibitor BMS-566419 on rat cardiac allograft rejection

Inosine 5'-monophosphate dehydrogenase (IMPDH) inhibition is a critical target in solid organ transplantation, and the development of mycophenolate mofetil (MMF) represents a major advance in transplant medicine. In this study, the in vitro and in vivo pharmacological effects of BMS-566419, a novel chemically synthesized IMPDH inhibitor, were compared to those of mycophenolic acid (MPA) and MMF based on results from several immunological experiments. The in vitro inhibitory activity of BMS-566419 on IMPDH type I/II, immune cell proliferation and antibody production from lipopolysaccharide (LPS)-stimulated B cells was similar, albeit slightly less potent than that of MPA. In a rat heterotopic cardiac transplant model, monotherapy using orally administered BMS-566419 60mg/kg or MMF 40mg/kg prolonged the median survival time (MST) of transplanted grafts in the vehicle group from 5 to 18 and 18.5 days, respectively. In the presence of a sub-therapeutic dose of FK506, BMS-566419 30mg/kg and MMF 20mg/kg showed identical efficacy with an MST of 21.5 days. In dinitrophenol-LPS-stimulated rats in which calcineurin inhibitors failed to inhibit antibody production, in vivo oral administration of BMS-566419 resulted in antibody production suppression with similar efficacy to MMF. The in vivo antibody production against alloantigen was also suppressed by MMF or BMS-566419 treatment. In addition, gastrointestinal toxicity, considered a dose-limiting factor of MMF, was reduced in BMS-566419 treatment. These results suggest that BMS-566419 and other chemically synthesized IMPDH inhibitors have beneficial pharmacological effects similar to those of MMF, and are potential pharmaceutical candidates in transplant indications.

Population pharmacokinetics of mycophenolic acid and its 2 glucuronidated metabolites in kidney transplant recipients

The population pharmacokinetics of mycophenolic acid (MPA) and its phenolic (MPAG) and acyl (AcMPAG) glucuronide metabolites were studied in patients taking enteric-coated mycophenolate sodium. Plasma samples (n = 232), obtained from 18 renal transplant recipients, were analyzed for MPA, MPAG, and AcMPAG using a validated high-performance liquid chromatography/ultraviolet assay. Population pharmacokinetic analysis was performed using NONMEM. The pharmacokinetics of MPA were best described by a 2-compartment model, with MPAG and AcMPAG produced from the central compartment and with enterohepatic recirculation of MPA via these 2 metabolites. Population mean estimates for MPA were apparent clearance (CL/F) of 10.6 L/h (interindividual variability [IIV] = 21.4%) and apparent volume of distribution of the central compartment (V(1)/F) of 25.9 L (IIV = 87.8%). Mean elimination rate constants of MPAG and AcMPAG were 0.323 h(-1) (IIV = 29.1%) and 0.206 h(-1) (IIV = 48.8%), respectively. The mean fraction of MPA converted to MPAG and AcMPAG, normalized by their volumes of distribution (FM(AG) and FM(AC), respectively), was also estimated. The elimination rate constant for MPAG and FM(AC) was influenced by glomerular filtration rate in patients with renal impairment. The visual predictive check, based on 100 simulated data sets each for MPA, MPAG, and AcMPAG, found that the final pharmacokinetic model adequately predicts the observed concentrations of all 3 species.