Metformin Dosing Guide — India · Kidney Disease · eGFR Adjustment
| eGFR (mL/min/1.73m²) | CKD Stage | Metformin dose | Max daily | Action |
|---|
| >90 | G1 (normal/high) | 500mg BD → titrate up | 2000 mg | Full dose, routine monitoring |
| 60–90 | G2 (mildly decreased) | 500mg BD → titrate up | 2000 mg | Full dose, annual eGFR check |
| 45–59 | G3a (mild-moderate) | Standard dose with caution | 2000 mg | Monitor eGFR every 3–6 months |
| 30–44 | G3b (moderate-severe) | Maximum 500mg BD | 1000 mg | Halved max dose · monitor closely |
| <30 | G4–G5 (severe/failure) | CONTRAINDICATED | — | Stop metformin · seek alternative |
Metformin in Type 2 Diabetes — India Clinical Guide
Metformin (biguanide) is the first-line pharmacological treatment for type 2 diabetes mellitus (T2DM) in India, recommended by both the Indian Council of Medical Research (ICMR) and the American Diabetes Association (ADA) as the preferred initial agent when lifestyle modification alone is insufficient. It works primarily by reducing hepatic glucose output (gluconeogenesis) and improving peripheral insulin sensitivity, without causing hypoglycaemia in monotherapy or weight gain.
In India, where type 2 diabetes affects over 77 million people and a significant proportion have concurrent chronic kidney disease (CKD) at diagnosis, appropriate metformin dosing with renal function monitoring is one of the most clinically important prescribing decisions in primary care. Lactic acidosis — metformin's most serious rare adverse effect — occurs almost exclusively in patients with contraindications to its use, primarily renal impairment. Correct renal dose adjustment essentially eliminates this risk.
How to start metformin — titration for tolerability
The most common reason patients stop metformin is gastrointestinal side effects — nausea, diarrhoea, and abdominal bloating. These occur in up to 30% of patients but are largely avoidable with correct titration. The standard approach: start at 500 mg once daily with dinner. After 1 week, increase to 500 mg twice daily (with breakfast and dinner). After a further 1–2 weeks, increase to 500 mg three times daily or 1000 mg twice daily, depending on tolerability and glycaemic response. The target dose for most patients is 1000–2000 mg/day. Extended-release (SR) formulations (Glycomet SR) have lower GI side effect rates and can be substituted for immediate-release if GI intolerance is significant.
Metformin and kidney disease — the eGFR thresholds that matter
Metformin is renally excreted almost entirely unchanged, with over 90% renal clearance. Accumulation in renal impairment increases lactic acid levels, as metformin inhibits mitochondrial complex I and shifts metabolism toward lactate production. The current evidence-based eGFR thresholds, per BNF, ADA, and KDIGO 2022 guidelines, are:
- eGFR ≥ 45 mL/min/1.73m²: Metformin may be used at standard doses. Annual eGFR monitoring recommended.
- eGFR 30–44 mL/min/1.73m² (CKD G3b): Metformin may be continued but the maximum daily dose should be halved (maximum 1000 mg/day). eGFR should be checked every 3–6 months.
- eGFR < 30 mL/min/1.73m² (CKD G4–G5): Metformin is contraindicated. Stop metformin and switch to an alternative glycaemic agent (SGLT2 inhibitor only if eGFR >20, GLP-1 RA, or sulphonylurea under supervision).
Note that the older threshold of eGFR <60 for stopping metformin — still seen in some older Indian guidelines — is no longer recommended. The current international consensus allows metformin at reduced doses down to eGFR 30, based on safety data from large observational studies. Use the eGFR Calculator on RxMedCalc to calculate the patient's current eGFR before prescribing.
When to hold metformin — perioperative and contrast guidance
Metformin must be temporarily discontinued in certain clinical situations to prevent lactic acidosis risk, even when the patient's baseline eGFR is adequate:
- Iodinated contrast media (CT, coronary angiography, IVP): Metformin should be held from the time of contrast administration and restarted 48 hours later, only if renal function is confirmed to be stable (eGFR unchanged from baseline). Contrast-induced nephropathy can transiently drop eGFR, causing metformin accumulation.
- Surgery requiring general or regional anaesthesia: Hold metformin on the day of surgery and for 48 hours post-operatively. Restart when the patient is eating, haemodynamically stable, and eGFR is checked.
- Acute illness with dehydration: Any illness causing significant dehydration, diarrhoea, or vomiting reduces renal perfusion and effective GFR, even if the baseline eGFR is normal. Hold metformin during the illness and restart when recovered and oral intake is restored.
- Hepatic impairment: Avoid metformin in hepatic failure, as impaired lactate clearance increases lactic acidosis risk.
Metformin and lactic acidosis — putting the risk in perspective
Lactic acidosis associated with metformin use is extremely rare when the drug is used correctly — estimated at approximately 3 cases per 100,000 patient-years. This rate is comparable to that seen in diabetic patients not on metformin, suggesting that lactic acidosis in these patients is often related to the underlying disease burden (sepsis, shock, cardiac failure) rather than metformin itself. The key message for Indian clinicians: metformin is safe in patients with eGFR ≥ 30 mL/min/1.73m², provided the drug is held during the recognised high-risk situations listed above.
Frequently Asked Questions
When should metformin be stopped in kidney disease?+
Metformin is contraindicated when eGFR falls below 30 mL/min/1.73m² (CKD G4–G5). Between eGFR 30–44 (CKD G3b), reduce the maximum daily dose to 1000 mg. Between 45–59 (CKD G3a), continue standard dose with careful monitoring. The old threshold of stopping at eGFR <60 is no longer recommended by ADA, KDIGO, or BNF.
What is the starting dose of metformin in India?+
Start metformin at 500 mg once daily with dinner. After 1 week, increase to 500 mg twice daily. Titrate every 1–2 weeks as tolerated, targeting 1000–2000 mg/day. Extended-release (SR) tablets cause less GI upset and can be given once daily at night — use Glycomet SR 500 or 1g as a once-daily starting option.
Should metformin be stopped before a CT scan with contrast in India?+
Yes. Hold metformin from the time of contrast injection and restart 48 hours later, provided renal function is stable. Contrast-induced nephropathy can transiently impair renal function, causing metformin accumulation. This applies to coronary angiography, contrast CT, IVP, and any iodinated contrast procedure. It is standard practice in India to hold metformin for 48 hours post-contrast regardless of baseline eGFR.
Can metformin cause hypoglycaemia?+
No. Metformin does not cause hypoglycaemia when used as monotherapy, because it reduces hepatic glucose output and sensitises insulin receptors without stimulating insulin secretion. Hypoglycaemia can occur when metformin is combined with sulphonylureas (e.g. glibenclamide) or insulin — in that case, the risk is from the sulphonylurea or insulin, not the metformin.
What is the difference between Glycomet 500 and Glycomet SR 500 in India?+
Glycomet 500 is immediate-release metformin — absorbed and excreted within 6–8 hours, usually given 2–3 times daily. Glycomet SR (sustained-release) releases metformin slowly over 12+ hours, allowing once-daily or twice-daily dosing. SR has lower GI side effects and better tolerability. It is preferred for patients with significant GI side effects on IR tablets, and for once-daily convenience. The SR formulation is generally taken with dinner.
⚠️
This calculator is a clinical decision-support tool for trained healthcare professionals. Always verify doses against the BNF, ADA guidelines, and ICMR Standards of Medical Care in Diabetes — India. Clinical judgement must be applied. Not a substitute for professional medical advice.
Related Tools