Metformin as RenoProtector of Progressive Kidney Disease

Inclusion Criteria: * Adult patients (≥18 years) of both gender * Seen on a regular base in one of the participating outpatient clinics of renal care with a previous consultation within the last year * Having a chronic kidney disease (including having a transplant kidney for more than 3 years) with: * a CKD stage 2, 3A or 3B (i.e. with estimated glomerular filtration rate (eGFR) between 30 and 70 ml/min/1.73m2) at the time of the baseline visit * showing a decline of eGFR between 3.0 and 20.0 ml/min/year determined using at least three determinations of eGFR (CKD-Epi formula) whereby the oldest one should be from more than 1 year ago and the most recent will be the one of the baseline visit. For transplant patients the decline will be based on serum creatinine values determined during the preceding 24 months. For all other patients, the decline will be based on values determined within the last five years Exclusion Criteria: 1. Illiteracy: patients not knowing how to read or write 2. Patients not able to communicate in Dutch or French 3. Patients with mental deterioration, incapable to give informed consent and to understand the safety instructions of the study (at the discretion of the treating nephrologist) 4. Patients with one of the following clinical problems: * Patients with nephrotic syndrome * Patients showing a fast decline of renal function (more than 20 ml/min/year) during the preceding five years * Diabetes mellitus (any type: 1, 2, Maturity Onset Diabetes of the Young (MODY), New Onset Diabetes After Transplantation (NODAT)) confirmed by a glycemia level \>125 mg/dl (7.0 mmol/L) after a fasting time of 8 hours * Patients with a renal transplantation for less than 3 years * Patients with multi-organ transplantation * History of other solid organ transplantations * Chronic obstructive pulmonary disease (COPD) stage Gold IV (Oxygene-dependency) * Congestive heart failure (NYHA stage IV) * Inflammatory bowel disease (IBD) * Stoma * Hepatic insufficiency or cirrhosis, acute alcohol intoxication or alcoholism (\> 20 glasses of alcoholic beverages per week) * History of metabolic diseases (e.g. mitochondrial encephalomyopathy (MELAS), lactic acidosis, stroke-like episodes, etc…) * Pregnancy and/or lactating women at the time of recruitment and during the study period * Patient with prior use of metformin within the past 12 months (e.g. glucose intolerance, polycystic ovary syndrome, etc…) or with other study medication taken within the framework of another clinical trial 5. Patients showing elevated blood lactate level(s) at the time of recruitment (i.e. a confirmed lactate level ≥ 2.5 mmol/L at baseline and a confirmed lactate level ≥ 2.5 mmol/L after 4 weeks (±1 week)). 6. Patients showing a confirmed (after 3 months) serum bicarbonate level \< 22 mmol/L (or \< 20 mmol/L if delay of more than 1 hour between sampling and determination) 7. Hypersensitivity to metformin or to any of the excipients listed in section 6.1 of the Glucophage SR SmPC (see Attachment A5 Glucophage SR SmPC) 8. One of the following diseases during the previous 6 months: myocardial infarction, shock, acute problems of decompensated heart failure or respiratory failure.