Implementation of Metformin theraPy to Ease Decline of Kidney Function in Polycystic Kidney Disease (IMPEDE-PKD)

Inclusion Criteria:

To be eligible to participate in this trial, patients must satisfy all of the following inclusion criteria:

1. Willing to participate and provide informed consent

2. Aged 18-70 years

3. Diagnosis of ADPKD based on radiological +/- genetic criteria as per Kidney HealthAustralia - Caring for Australians and New Zealanders with Kidney Impairment (KHA-CARI) Guidelines

4. eGFR equal to or greater than 38 mL/min/1.73m2 and <90 mL/min/1.73m2

And have either:

5(a) One or more risk factors of progression from the following:

• Bilateral kidney length equal to or greater than16.5 cm, or

• Total Kidney Volume (TKV) equal to or greater than 750 mL or height-adjusted TKV (htTKV) equal to or greater than 600 mL/m2, or

• Mayo class IC/D/E or Pro-PKD score equal to or greater than 6 OR 5(b) Evidence ofActive progression

• Decline in eGFR equal to or greater than 5 mL/min/1.73m2 in one year, or

• Decline in eGFR equal to or greater than 3 mL/min/1.73m2 per year over five years ormore. or

• Increase in htTKV/TKV of equal to or greater than 5% per year on at least 2measurements in the past year, excluding any initial eGFR effect over the initial 3months of tolvaptan commencement (if applicable) Note: Tolvaptan therapy must havebeen in place for at least 6 months with stable dose for at least 3 months.

Exclusion Criteria:

1. Diabetes mellitus (as per American Diabetes Association definition), or othersystemic conditions that may cause CKD independent of PKD (excluding hypertension)

2. Uncontrolled hypertension (Systolic BP >160 mmHg and/or diastolic BP >100 mmHg aftera period of rest)

3. Clinically significant heart failure, including but not limited to New York HeartAssociation Class (NYHA) III or IV

4. Non-polycystic liver disease, including but not limited to:

5. Liver enzymes (ALT, AST or Total Bilirubin) >2 times the upper limit of normal,except when a diagnosis of Gilbert Syndrome exists and/or,

6. Child-Pugh classification score equal to or greater than 5

7. Any contraindication to metformin including abnormal liver function tests oruntreated Vitamin B12 deficiency

8. Currently taking metformin

9. Pregnancy or breastfeeding, or planning to get pregnant in the next three years.

10. Comorbidities with potential to contaminate trial outcomes, specifically activecancer, history of other solid organ transplantations, active chronic obstructivepulmonary disease (COPD), active inflammatory bowel disease, and the presence ofstoma.

11. History of dialysis.