Development of New-Onset Diabetes after Transplantation (NODAT) is common and serious complication after kidney transplantation. Patients who develop NODAT are at increased risk for loss of the transplanted organ and for diseases of the cardiovascular system.

It is believed that in many patients the development of overt NODAT is preceded by a phase of impaired glucose tolerance that is called pre-diabetes.

This study aims at improving glucose metabolism in patients after kidney transplantation who are in a pre-diabetic metabolic state. Patients who exhibit impaired glucose tolerance (IGT) after kidney transplantation are randomized to either receive vildagliptin (Galvus), pioglitazone(Actos) or placebo for three months.

The investigators hypothesize that treatment with vildagliptin or pioglitazone leads to improved glycemic control compared to placebo.

Inclusion Criteria:

• Time since renal transplantation > 6 months
• Stable graft function
• Routine OGTT has been performed, and pre-diabetes has been diagnosed by pathological OGTT (2h, 75 g glucose, glucose level between 140 and 200 mg/dl)
• Informed consent of the patient

Exclusion Criteria:

• Patients with type 1 or type 2 diabetes
• Patients with NODAT (2h glucose level at OGTT >200 mg/dl)
• allergy against vildagliptin or pioglitazone
• pregnancy
• GFR<15ml/min/1.73 with need for dialysis
• hepatic impairment