Among the different creatinine-based GFR predicting equations, the MDRD equation gives the best prediction in renal transplantation but does not provide the level of accuracy usually seen in renal patients with native kidneys.

Blocking the tubular secretion of creatinine with an oral administration of cimetidine is likely to make creatinine a more accurate marker of GFR.

We will test the hypothesis that the accuracy of the MDRD equation will be improved in renal transplant patients by incorporating into the equation a cimetidine-corrected serum creatinine value.

Inclusion Criteria:

• Kidney transplantation > 1 year
• Patient with immunosuppressant treatment of TACROLIMUS (PROGRAF)
• Creatinine clearance > 30 ml/min/1,73m2 within 3 months before inclusion
• Written informed consent
• Patient affiliated to social insurance

Exclusion Criteria:

• Unstable renal function defined by serum creatinine (J0) > 25% serum creatinine realised in 3 months
• Treatment: Bactrim, Fansidar, Cimetidine arrow within the week before inclusion
• Contraindication listed in the labeling of Cimetidine arrow
• Last residual rate of Tacrolimus > 12 ng/ml.
• Treatment : carvedilol, phenytoïn (interaction with cimetidine)
• Serious hepatic insufficiency