 Mycophenolate sodium Myfortic is an antiproliferative immunosuppressant used in renal transplantation. Mycophenolate sodium is formulated as an enteric coated tablet that releases mycophenolic acid MPA which in turn inhibits inosine monophosphate dehydrogenase IMPDH. Through inhibition of IMPDH, the de novo pathway of purine synthesis, which T and B lymphocytes rely on for proliferation, is blocked. The pharmacokinetic profile of mycophenolate sodium has mainly been studied in combination with cyclosporine and steroids. There is little information on the pharmacokinetics of mycophenolate sodium in combination with tacrolimus and currently no published information in steroid withdrawal. All current published data on the pharmacokinetics of MPA have been in patients receiving chronic corticosteroids as part of their immunosuppression regimen. As immunosuppression minimization, and especially corticosteroid withdrawal, become more popular it is important to understand how mycophenolate sodium and its metabolites behave in a two-drug maintenance immunosuppression regimen. The study will assess the pharmacokinetic profile of mycophenolate sodium in patients on tacrolimus dose adjusted based on levels, and a steroid withdrawal protocol. 