MMF is the morpholinoethylester prodrug of mycophenolic acid (MPA). After oral administration MMF is well absorbed and rapidly hydrolyzed to MPA. MPA is a noncompetitive inhibitor of inosine monophosphate (IMP) dehydrogenase (DH). Inhibition of IMPDH leads to the depletion of deoxyguanosine triphosphate and a consequent decrease in the level of substrate required for DNA polymerase activity. This results in inhibition of DNA production and cell proliferation. T and B cells are more dependent on this de novo pathway of purine synthesis because alternative salvage pathways are unavailable. Thus, MPA is a selective inhibitor of lymphocyte proliferation, especially in activated lymphocytes (Allison & Eugui 2000).