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.