Measurement of Total and Unbound Mycophenolic Acid and Its Glucuronide by LC Coupled with MS. Application to a Pharmacokinetic Study of Mycophenolate Mofetil in Patients with Autoimmune Diseases

Pre-dose plasma concentration monitoring of mycophenolate mofetil in patients with autoimmune diseases

AIM

To date, neither the benefit of mycophenolic acid (MPA) therapeutic drug monitoring (TDM), the prodrug of mycophenolate mofetil (MMF), nor the optimal monitoring technique have been established in autoimmune diseases. This study was undertaken to confirm, in a cohort of new patients, the plasma MPA thresholds previously published in patients with systemic lupus erythematosus (SLE) or vasculitis.

METHODS

MPA areas under the concentration-time curves between 0 and 12 h, 12 h trough concentrations and pre-dose concentrations (C0 ) were determined for 23 patients with SLE and 21 with systemic vasculitis. The relationship between patients' pharmacokinetic (PK) variables and their clinical outcomes during follow-up were analyzed.

RESULTS

In both autoimmune diseases, at PK assessment, median MPA C0 for patients with uncontrolled disease was significantly lower than that of patients with stable disease or in remission, 1.6 mg l(-1) (IQR 0.9-2.1 mg l(-1)) vs. 2.95 mg l(-1) (IQR 1.38-3.73 mg l(-1)) for SLE (P = 0.048) and 1.55 mg l(-1) (IQR 0.98-2.18 mg l(-1)) vs. 3 mg l(-1) (IQR 2.2-4.4 mg l(-1)) for vasculitis (P = 0.016). According to our receiver operating characteristics curve analysis, a C0 threshold of 2.5-3 mg l(-1) was best able to discriminate a flare (SLE: 88% sensitivity, 80% specificity; vasculitis: 100% sensitivity, 90% specificity). Patients with C0 ≥ 2.5-3 mg l(-1) at inclusion had better clinical outcomes during the 12 months following PK assessment.

CONCLUSION

Provided that the benefit of TDM in patients with autoimmune diseases could be confirmed by randomized, controlled trials, it might be based on the C0 measured approximately 12 h post-dose.

Steady-state mycophenolate mofetil pharmacokinetic parameters enable prediction of systemic lupus erythematosus clinical flares: an observational cohort study

Introduction

The aim of this study was to determine whether mycophenolate mofetil (MMF) pharmacokinetics (PK) under combined MMF and prednisone remission-maintenance therapy can predict systemic lupus erythematosus (SLE) clinical flares.

Methods

At inclusion, steady-state PK parameters of the MMF active form, mycophenolic acid (MPA), and its glucuronide metabolite (MPAG) were determined for 25 stable SLE patients without renal manifestations. Disease activity was assessed during 6 months of follow-up. Potential relationships between those entry MMF-PK variables and clinical outcome were analyzed.

Results

MMF controlled disease activity in 17 patients (successes) and failed to do so for 8 others (failures). For failures and successes, respectively, entry MPA areas under the time-concentration curve between 0 and 12 hours (AUC_{0-12 h}) (medians: 37.7 vs 73.1 mg/h/L, P = 0.003) and MPA 12-hour trough concentrations (C_{12 h}) (medians: 1.5 vs 3.7 mg/L, P = 0.008) were significantly lower, and inclusion MPAG/MPA C_{12 h} ratios (medians: 18.7 vs 10.2, P = 0.02) were significantly higher. According to our receiver operating characteristics curve analysis, MPA C_{12 h} was best able to discriminate a flare during follow-up (93% sensitivity, 85% specificity). A 3-mg/L cut-off had 92% negative-predictive value for developing a flare during follow-up.

Conclusions

For our SLE patients without renal manifestations, clinical flares developing under maintenance therapy were associated with steady-state inclusion MPA C_{12 h} < 3 mg/L.

Determination of mycophenolic acid and its phenyl glucuronide in human plasma, ultrafiltrate, blood, DBS and dried plasma spots

Background: Analysis of mycophenolic acid (MPA), the active form of the immunosuppressive drug mycophenolate mofetil, and its glucuronide metabolite MPAG is required for therapeutic monitoring and postmarketing clinical studies. Dried blood spots (DBS) and dried plasma spots (DPS) could be alternatives to conventional assays for small-volume sampling and easy shipment. Results: A LC–MS/MS method with online SPE was established using stable isotope labeled analytes as internal standards. The quantitation limits were set at 0.1 and 1 µg/ml, for total MPA and MPAG, respectively, in plasma, blood, DBS and DPS, but 100-fold lower for free MPA in ultrafiltrate. Ahlstrom 226 or Whatman FTA® DMPK-B cards were well suited for DBS and DPS analyses. Conclusion: MPA and MPAG were analyzed in human plasma and blood either as liquid or dried on cards with similar assay quality. Care should be taken to avoid back-conversion of an instable acyl glucuronide metabolite to MPA.