- Impaired renal function defined as serum-creatinine at least 133 mcmol/l (at least 1.5 mg/dl) for males and at least 125 mcmol/l (at least 1.4) for females, or as allowed according to local contraindications for metformin (one retest analysed at the central laboratory within a week from first sample taken is permitted with the result of the last sample being the conclusive)