Mycophenolate mofetil (MMF) is widely used in the field of solid organ transplantation. In combination with calcineurin inhibitors it has become the most often used drug to prevent acute rejection. In an attempt to reduce the incidence of the gastrointestinal adverse events associated with MMF use, the enteric-coated mycophenolate sodium (EC-MPS) was developed. Unfortunately, in two clinical trials EC-MPS 720 mg twice daily and MMF 1000 mg twice daily showed similar efficacy and safety profiles. The two formulations are therefore considered to be therapeutically equivalent. MPA exposure, measured as the area under the plasma concentration time curve (AUC), does not differ during administration of bioequivalent dosages of the two drugs (720 mg EC-MPS and 1000 mg MMF). Also the pharmacodynamic effect, measured as inhibition of the target enzyme inosine monophosphate dehydrogenase (IMPDH) has been shown to be comparable between the two formulations. However, due to the enteric coating the pharmacokinetic profile of EC-MPS is different, with a longer and more variable time to reach the peak concentration (T[sub]max[/sub]). This increased variability in pharmacokinetics impacts on the application of therapeutic drug monitoring in patients using EC-MPS. It is well known that the correlation between pre-dose concentrations and AUC is poor for MMF. At the same time we also realize that drawing full AUCs, consisting of 8-12 blood samples over the 12-hour dosing interval, poses practical problems in routine clinical practice. Therefore limited sampling strategies have successfully been developed, in order to reliably estimate AUC, using only 2 or 3 samples obtained in the first few hours after oral MMF intake. Such limited sampling strategies however require reproducible pharmacokinetic profiles. In contrast to MMF the profiles obtained with EC-MPS show too much variability to develop reliable limited sampling strategies. This implies that the only method to reliably measure the MPA-AUC in a patient treated with EC-MPS is to perform a full (8-12 blood sample) AUC curve.

Keywords: Mycophenolate Mofetil, Organ Transplantation, plasma concentration