 A relationship between MPA exposure and acute rejection beyond 3 months has not been demonstrated. There is a paucity of studies examining the concentration-effect relationship beyond the first post transplant year and thus there are no established recommendations for MPA exposure after the first post-transplant year. In clinical practice a significant proportion of long-term 1 year post transplant MPA treated patients will be prescribed less than the recommended dose of MPA due to a variety of reasons including patient intolerance usually gastrointestinal or hematological. Most reductions in MPA dose are undertaken in the first few months after transplantation when renal allograft dysfunction or hypoalbuminemia may have increased free MPA exposure and possibly increased drug related side effects. Importantly recent controlled studies in both de novo and maintenance transplant patients have demonstrated the safety of once daily MPA dosing using less than the initial recommended daily dose. 