The definition and classification of chronic kidney disease (CKD) have evolved over time, but current international guidelines define this condition as decreased kidney function shown by glomerular filtration rate (GFR) of less than 60 mL/min per 1·73 m2, or markers of kidney damage, or both, of at least 3 months duration, regardless of the underlying cause.Diabetes and hypertension are the main causes of CKD in all high-income and middle-income countries, and also in many low-income countries. Regarding to diabetic patient . Metformin is recommended as a first-line treatment for patients with type 2 diabetes. However, use of this drug has been contraindicated in individuals with impaired kidney function because of the perceived risk of lactic acidosis. Evidence now supports cautious use of metformin in people with mild-to-moderate chronic kidney disease. However, studies examining the use of metformin in patients with advanced chronic kidney disease are lacking. In this study they  assess the safety of metformin in patients with type 2 diabetes and advanced (approximately stage 5) chronic kidney disease.

If you are interested to know more  in the link attached

http://www.thelancet.com/journals/landia/article/PIIS2213-8587(15)00123-0/fulltext