Sequential determination of pharmacokinetics and pharmacodynamics of mycophenolic acid in liver transplant patients treated with mycophenolate mofetil

Background. In liver transplantation, mycophenolate mofetil (MMF) is habitually ad ministered using fixed doses. We assessed whether mycophenolic acid (MPA) monitoring could be advisable in liver transplant patients. Methods. In 15 liver transplant patients receiving tacrolimus, daclizumab and MMF (1 g bid, orally), we determined the 12-hour plasma MPA pharmacokinetic profile after one dose of MMF at days 6, 10, and 16, and months 3 and 6. The inhibitory capacity of serum MPA on proliferation of CEM cells, a cell line insensitive to other immunosuppressants, was also determined. Results. A large interindividual variability in MPA profiles was observed at any time. Regardless of a gradual increase in individual MPA AUC and C-0 over time following transplantation, a Substantial proportion of patients had these parameters below the ranges recommended in other organ transplantations throughout the study. When MPA AUC and C-0 were within the recommended ranges, CEM proliferation was inhibited by almost all serum samples, but when these pharmacokinetic parameters were below the recommended ranges, CEM proliferation was very variable and, therefore, unpredictable. No relationship between MPA pharmacokinetics and the efficacy of MMF could be established (only one patient developed rejection), probably due to the concomitant administration of tacrolimus and daclizumab. Gastrointestinal symptoms were the only adverse events with a significant relationship with MPA levels. Conclusions. During the first postoperative months, exposure to MPA is low in a considerable proportion of liver transplant patients receiving MMF at a fixed dose of I g bid. MPA monitoring appears necessary in these patients.