Mycophenolate mofetil in patients with acute renal failure: evidence of metabolite (MPAG) accumulation and removal by dialysis

Increased levels of a mycophenolic acid metabolite in patients with kidney failure negatively affect cardiomyocyte health

Chronic kidney disease (CKD) significantly increases cardiovascular risk and mortality, and the accumulation of uremic toxins in the circulation upon kidney failure contributes to this increased risk. We thus performed a screening for potential novel mediators of reduced cardiovascular health starting from dialysate obtained after hemodialysis of patients with CKD. The dialysate was gradually fractionated to increased purity using orthogonal chromatography steps, with each fraction screened for a potential negative impact on the metabolic activity of cardiomyocytes using a high-throughput MTT-assay, until ultimately a highly purified fraction with strong effects on cardiomyocyte health was retained. Mass spectrometry and nuclear magnetic resonance identified the metabolite mycophenolic acid-β-glucuronide (MPA-G) as a responsible substance. MPA-G is the main metabolite from the immunosuppressive agent MPA that is supplied in the form of mycophenolate mofetil (MMF) to patients in preparation for and after transplantation or for treatment of autoimmune and non-transplant kidney diseases. The adverse effect of MPA-G on cardiomyocytes was confirmed in vitro, reducing the overall metabolic activity and cellular respiration while increasing mitochondrial reactive oxygen species production in cardiomyocytes at concentrations detected in MMF-treated patients with failing kidney function. This study draws attention to the potential adverse effects of long-term high MMF dosing, specifically in patients with severely reduced kidney function already displaying a highly increased cardiovascular risk.

Pharmacokinetics of mycophenolic acid and its phenyl glucuronide metabolite in kidney transplant recipients with renal impairment

INTRODUCTION

The aim of the study was to analyse the influence of renal impairment on the pharmacokinetic parameters (PK) of mycophenolic acid (MPA) and its glucuronide metabolite (MPAG) in renal transplant recipients.

MATERIAL AND METHODS

The study included 43 adult patients during the maintenance period (> 6 months) following renal transplantation, treated with mycophenolate mofetil (MMF), calcineurin inhibitors (CNI) (tacrolimus or cyclosporine) and steroids. The study compared patients with normal renal function (n = 17; creatinine clearance (C(cr)) > 60 ml/min) and with renal impairment (n = 26; C(cr) < 60 ml/min). Areas under the 4-h curve (AUC(0-4 h)) of MPA and MPAG were determined using a validated HPLC method.

RESULTS

The renal impairment group showed significantly increased AUC(0-4 h) and pre-dose (C(0)) for MPAG compared to patients with normal renal function and increased MPA C(0). However, there was no significant difference in MPA AUC(0-4 h) between patients with renal impairment and patients with normal renal function. In multivariate analysis some MPA and MPAG PK parameters were correlated with sex, CNI co-administered and body weight.

CONCLUSIONS

Although MPAG is an inactive metabolite, its accumulation in patients with renal impairment can be unfavourable. The results of our study indicate that solely MPA C(0) determination in patients receiving MMF may be insufficient in clinical practice because of great inter-patient variability of this PK parameter caused mainly by enterohepatic recirculation.

Clinical review: Drug metabolism and nonrenal clearance in acute kidney injury

Decreased renal drug clearance is an obvious consequence of acute kidney injury (AKI). However, there is growing evidence to suggest that nonrenal drug clearance is also affected. Data derived from human and animal studies suggest that hepatic drug metabolism and transporter function are components of nonrenal clearance affected by AKI. Acute kidney injury may also impair the clearance of formed metabolites. The fact that AKI does not solely influence kidney function may have important implications for drug dosing, not only of renally eliminated drugs but also of those that are hepatically cleared. A review of the literature addressing the topic of drug metabolism and clearance alterations in AKI reveals that changes in nonrenal clearance are highly complicated and poorly studied, but they may be quite common. At present, our understanding of how AKI affects drug metabolism and nonrenal clearance is limited. However, based on the available evidence, clinicians should be cognizant that even hepatically eliminated drugs and formed drug metabolites may accumulate during AKI, and renal replacement therapy may affect nonrenal clearance as well as drug metabolite clearance.