Correlation of mycophenolic acid pharmacokinetic parameters with side effects in kidney transplant patients treated with mycophenolate mofetil

Mycophenolate mofetil (MMF) is widely used in organ transplantation to prevent acute rejection. Because MMF can produce hematologic and/or gastrointestinal toxicity, therapeutic monitoring is becoming mandatory. This study was designed to investigate the relationship between the clinical events and the pharmacokinetics of mycophenolic acid (MPA) in adult renal transplantation.

Thirty-one adult kidney recipients were prospectively included in the study. MPA pharmacokinetic profiles (blood sampling at 0, 0.5, 1, 2, 4, 6, and 12 h after MMF oral dose) were obtained after transplantation (desired creatinine clearance, 40 mL/min), at 3 months after grafting, and at every clinical event (e.g., side effect or rejection). All patients received a 10-day course of anti-thymocyte globulin, cyclosporine, MMF (1 g twice daily), and steroids.

We divided the 31 patients into two groups (groups 1 and 2). Ten patients (32%; group 1) had uneventful outcomes, and 21 patients (68%; group 2) presented with MPA-related side effects. For groups 1 and 2, the MPA trough concentrations (C(min)) were 1.63 +/- 1.07 and 2.29 +/- 1.16 mg/L, respectively (P = 0.06), and the areas under the curve (AUCs) for MPA from t(0) to t(12 h) (MPA-AUC(0-12h)) were 39.80 +/- 15.29 and 62.10 +/- 21.07 mg. h/L, respectively (P = 0.0005, two-sample t-test). Three patients experienced acute graft rejection after the oral MMF dose was reduced because of side effects. In this group, the MPA-C(min) and MPA-AUC were significantly lower by the time acute rejection occurred (1.00 +/- 0.45 mg/L and 25.00 +/- 6.20 mg. h/L, respectively). At a fixed dose (1 g twice per day), we compared the pharmacokinetic parameters of MPA [C(min), the MPA concentration 30 min after the oral dose of MMF (C(30)), and AUC] according to the presence or absence of side effects in the two groups. C:(min) and AUC did not differ between the two groups [C(min) = 2.22 +/- 1.13 vs 2.17 +/- 1.13 mg/L (P = 0.9); AUC = 66.82 +/- 29.87 vs 55.70 +/- 11.74 mg. h/L (P = 0.11)]; and C(30) was significantly higher in group 2 than in group 1 (C(30) = 32.99 +/- 12.59 vs 7.45 +/- 5.40 mg/L; P <0.0001).

Our results demonstrate a pharmacokinetic/pharmacodynamic relationship between MPA and clinical events. At a fixed dose of 2 g/day, a high C(30) is associated with increased risk for side effects. This study suggests that dividing the MMF daily oral dose into more than two divided doses might prevent early MPA toxicity.