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Metformin Uses, Dosage, Side Effects & Benefits | DrugsAtlas

Authoritative Clinical Reference

Therapeutic Class

Antidiabetic Agent

Subclass

Biguanide

Speciality

Endocrinology

Schedule (India)

Schedule H

Routes

Oral

Formulations

Tablets (Immediate-release): 250 mg, 500 mg, 850 mg, 1000 mg
Tablets (Modified-release/Sustained-release/Extended-release): 500 mg, 750 mg, 1000 mg
Oral solution: NOT AVAILABLE in India as monotherapy

Fixed-Dose Combinations (FDCs) Available:

Metformin + Glimepiride
Metformin + Gliclazide
Metformin + Glipizide
Metformin + Vildagliptin
Metformin + Sitagliptin
Metformin + Linagliptin
Metformin + Teneligliptin
Metformin + Empagliflozin
Metformin + Dapagliflozin
Metformin + Canagliflozin
Metformin + Pioglitazone

Adult indications

INDICATIONS + DOSING — FOR CLINICIAN USE ONLY

Primary Indications (Approved / Standard in India)

1. Type 2 Diabetes Mellitus (Monotherapy or Combination Therapy)

First-line pharmacological therapy along with lifestyle intervention as per ICMR Guidelines 2018

Immediate-Release Formulation:

Parameter	Dose
Starting dose	500 mg orally once or twice daily with meals
Titration	Increase by 500 mg every 7–14 days based on glycaemic response and GI tolerability
Usual maintenance dose	1500–2000 mg/day in 2–3 divided doses with meals
Maximum dose	2550 mg/day (in divided doses)

Modified-Release/Extended-Release Formulation:

Parameter	Dose
Starting dose	500 mg orally once daily with evening meal
Titration	Increase by 500 mg every 1–2 weeks based on glycaemic response
Usual maintenance dose	1500–2000 mg once daily with evening meal
Maximum dose	2000 mg/day (once daily)

Clinical Notes:

Administer with meals to reduce GI side effects
MR/SR/XR formulations should be swallowed whole; do not crush or chew
Reduces hepatic glucose output and improves peripheral insulin sensitivity
Does not cause hypoglycaemia when used as monotherapy
Provides modest weight loss or weight neutrality (advantage over sulfonylureas)
Continue metformin when adding other antidiabetic agents including insulin (unless contraindicated)

2. Polycystic Ovary Syndrome (PCOS)

For metabolic and reproductive benefits; used for insulin resistance, menstrual irregularity, and ovulation induction

Parameter	Dose
Starting dose	500 mg orally once daily with food
Titration	Increase by 500 mg every 1–2 weeks to improve GI tolerance
Usual maintenance dose	1500–2000 mg/day in 2–3 divided doses
Maximum dose	2550 mg/day (typically ≤2000 mg/day in practice)

Clinical Notes:

Benefits include improved insulin sensitivity, restoration of ovulation, and menstrual regularity
May be used alone or with clomiphene for ovulation induction
Weight loss and lifestyle modification should accompany pharmacotherapy
Continue for at least 3–6 months to assess efficacy
Not a substitute for lifestyle intervention

Secondary Indications – Adults (Off-label)

Indication	Dose	Duration	Supervision	Evidence Basis
Prevention of Type 2 Diabetes in High-Risk Individuals (Prediabetes/IFG/IGT) (OFF-LABEL)	Starting: 500 mg once daily; Titration: increase to 500–1000 mg twice daily as tolerated; Maintenance: 1000–1700 mg/day	Long-term; indefinite if risk factors persist	Specialist recommended	DPP trial; Indian Diabetes Prevention Programme (IDPP) data; ICMR guidance for high-risk individuals with metabolic syndrome not responding to lifestyle alone
Gestational Diabetes Mellitus (GDM) — Alternative to Insulin (OFF-LABEL)	Starting: 500 mg once or twice daily; Titration: increase by 500 mg/week; Maintenance: 1000–2500 mg/day in divided doses	Duration of pregnancy	Specialist only (Obstetrician/Endocrinologist)	MiG trial; Indian obstetric practice; used when insulin is declined, unavailable, or as adjunct
Antipsychotic-Induced Weight Gain and Metabolic Syndrome (OFF-LABEL)	500–2000 mg/day in divided doses	Long-term as needed	Specialist only (Psychiatrist)	RCTs showing benefit in clozapine/olanzapine-induced weight gain; Indian psychiatric practice
Non-Alcoholic Fatty Liver Disease (NAFLD) with Insulin Resistance (OFF-LABEL)	1000–2000 mg/day in divided doses	Long-term	Specialist recommended (Gastroenterology/Endocrinology)	Limited evidence; may improve insulin resistance but no proven effect on liver histology; used in Indian practice for associated metabolic syndrome

Paediatric indications

PAEDIATRIC DOSING (Specialist Only)

⚠️ Not recommended in children below 10 years of age except under specialist endocrinology supervision.

Primary Indication: Type 2 Diabetes Mellitus (Children ≥10 years)

Immediate-Release Formulation:

Parameter	Dose
Starting dose	500 mg orally once daily with meals
Titration	Increase by 500 mg every 1–2 weeks based on glycaemic response and GI tolerability
Usual maintenance dose	1000–2000 mg/day in 2–3 divided doses
Maximum dose	2000 mg/day

Modified-Release/Extended-Release Formulation (Children ≥10 years):

Parameter	Dose
Starting dose	500 mg orally once daily with evening meal
Titration	Increase by 500 mg every 1–2 weeks
Usual maintenance dose	1000–2000 mg once daily
Maximum dose	2000 mg/day

Safety Monitoring:

Monitor for GI intolerance (nausea, diarrhoea, abdominal pain)
Renal function at baseline and annually
HbA1c every 3 months
Growth and development monitoring
Vitamin B12 levels annually if on long-term therapy

Clinical Notes:

Always combine with lifestyle intervention (diet, physical activity)
Preferred first-line agent in paediatric Type 2 DM per IAP guidelines
Start low and titrate slowly to minimise GI side effects

Secondary Indications – Paediatrics (Off-label)

Indication	Age	Dose	Duration	Supervision	Evidence Basis
Polycystic Ovary Syndrome (PCOS) in Adolescent Girls (OFF-LABEL)	≥12 years	Starting: 500 mg once daily; Titration: increase by 500 mg every 1–2 weeks; Maintenance: 1000–2000 mg/day in divided doses; Maximum: 2000 mg/day	≥6 months; reassess periodically	Specialist only (Paediatric Endocrinology/Adolescent Gynaecology)	IAP adolescent PCOS guidelines; Indian paediatric endocrinology practice
Obesity with Insulin Resistance (OFF-LABEL)	≥10 years	500–2000 mg/day in divided doses	Long-term with lifestyle intervention	Specialist only (Paediatric Endocrinology)	Limited evidence; used as adjunct to lifestyle modification in severe obesity with metabolic complications

Age Restrictions:

Not recommended below 10 years of age for Type 2 DM
Use in children <10 years only under exceptional circumstances with paediatric endocrinology supervision
Not for Type 1 Diabetes (may be considered as adjunct in insulin-resistant T1DM under specialist care — very limited evidence)

Renal Adjustments

Metformin is renally excreted unchanged. Dose adjustment is mandatory in renal impairment due to risk of lactic acidosis.

eGFR (mL/min/1.73 m²)	Recommendation
≥60	No dose adjustment required
45–59	Use with caution; maximum 2000 mg/day; monitor eGFR every 3–6 months
30–44	Reduce dose; maximum 1000 mg/day; monitor eGFR every 3 months; not to be initiated if eGFR <45
<30	Contraindicated
Haemodialysis	Contraindicated
Peritoneal Dialysis	Contraindicated

Additional Notes:

Reassess eGFR before initiating and at least annually (more frequently if eGFR declining or risk factors present)
Withhold metformin temporarily during acute illness with risk of dehydration or AKI (sick day rules)
Withhold 48 hours before and after iodinated contrast administration if eGFR <60 or other risk factors for contrast-induced nephropathy

Hepatic adjustment

Contraindications

Severe renal impairment (eGFR <30 mL/min/1.73 m²)
Acute or chronic metabolic acidosis including diabetic ketoacidosis (DKA)
Conditions predisposing to lactic acidosis:
- Severe dehydration
- Shock (cardiogenic, septic, hypovolaemic)
- Acute or decompensated heart failure
- Acute myocardial infarction
- Severe hypoxia (respiratory failure, severe COPD exacerbation)
Severe hepatic impairment / Hepatic failure
History of lactic acidosis
Chronic alcohol abuse or acute alcohol intoxication
48 hours before and after surgery requiring general anaesthesia (due to risk of acute renal impairment)
Known hypersensitivity to metformin

Cautions

Chronic kidney disease (eGFR 30–60) — requires dose adjustment and close monitoring
Elderly patients — often have reduced renal reserve; assess eGFR before and during therapy
Conditions predisposing to dehydration (diarrhoea, vomiting, fever) — temporarily withhold metformin
Congestive heart failure (stable NYHA Class I-II may use with caution; avoid in Class III-IV)
Excessive alcohol intake (increased lactate production)
Planned iodinated contrast procedures — withhold 48 hours before and after; resume only after confirming stable renal function
Concurrent use of nephrotoxic drugs
Patients undergoing major surgery — temporarily discontinue
Vitamin B12 deficiency risk with long-term use — monitor periodically

Pregnancy

Parameter	Information
Overall Safety	Limited but reassuring human data; no confirmed teratogenicity; considered acceptable when indicated
Risk	Crosses placenta; theoretical concerns about fetal effects not substantiated in clinical studies
Preferred Alternatives	Insulin is first-line for GDM and pre-existing T2DM in Indian obstetric guidelines
When Use May Be Justified	GDM when insulin is declined, unavailable, or as adjunct to insulin for insulin resistance; PCOS-related infertility (may continue through first trimester with specialist guidance)
Monitoring	Maternal blood glucose (FBG, PPBG, HbA1c); fetal growth by serial ultrasound; monitor for neonatal hypoglycaemia after delivery

Lactation

Parameter	Information
Compatibility	Compatible with breastfeeding
Expected Drug Level in Milk	Very low (approximately 0.5–1% of weight-adjusted maternal dose reaches infant)
Risk to Infant	Minimal; no significant adverse effects reported in breastfed infants
Preferred Alternatives	None — metformin is preferred over sulfonylureas for glycaemic control in breastfeeding mothers with T2DM
Infant Monitoring	Feeding adequacy, weight gain (routine monitoring sufficient)

Elderly

Parameter	Recommendation
Starting dose	500 mg orally once daily with food
Titration	Increase slowly (every 2 weeks); assess tolerability and renal function frequently
Maximum recommended	Based on renal function; often limited to 1500–2000 mg/day
Increased Risks	Lactic acidosis (age-associated decline in renal function); GI intolerance; vitamin B12 deficiency
Additional Precautions	Assess eGFR before initiation and at least every 3–6 months; avoid in frail elderly with multiple comorbidities predisposing to lactic acidosis; use MR/XR formulations to improve GI tolerability; educate on sick day rules

Major drug interactions

Interacting Drug	Mechanism	Effect	Management
Iodinated Contrast Media	Contrast-induced nephropathy may impair metformin excretion	Increased risk of lactic acidosis	Withhold metformin 48 hours before and after contrast administration if eGFR <60 or other risk factors; resume only after confirming stable renal function
Excessive Alcohol	Alcohol increases lactate production and impairs gluconeogenesis	Significantly increased risk of lactic acidosis; risk of hypoglycaemia	Avoid excessive/binge alcohol consumption; moderate intake acceptable with caution
Cimetidine	Competes for renal tubular secretion	Increased metformin plasma levels (up to 50%)	Avoid combination or monitor closely; consider alternative H2 blocker (ranitidine, famotidine) or PPI
Dolutegravir	Inhibits renal tubular secretion of metformin (OCT2/MATE inhibition)	Increased metformin levels	Monitor for metformin adverse effects; consider dose reduction if GI intolerance develops

Moderate drug interactions

Interacting Drug	Effect	Management
ACE Inhibitors / ARBs	May impair renal function; potential for acute kidney injury	Monitor eGFR; adjust metformin dose if renal function declines
Loop Diuretics / Thiazides	Risk of dehydration and prerenal AKI; diuretics may worsen glucose tolerance	Monitor hydration status, renal function, and glycaemic control
NSAIDs	Risk of acute kidney injury, especially in dehydrated patients	Use with caution; ensure adequate hydration; monitor renal function
Corticosteroids (systemic)	Oppose glycaemic effects of metformin; may cause hyperglycaemia	Monitor blood glucose; may need temporary increase in metformin dose or addition of other antidiabetic agents
Beta-blockers	May mask hypoglycaemia symptoms (relevant when metformin combined with insulin/sulfonylureas)	Counsel patient on hypoglycaemia awareness; less relevant with metformin monotherapy
Carbonic Anhydrase Inhibitors (topiramate, acetazolamide)	May increase risk of lactic acidosis	Use with caution; monitor for acidosis symptoms
Vancomycin	Potential for additive nephrotoxicity	Monitor renal function closely
Rifampicin	Induces OCT1 transporter; may increase metformin uptake into hepatocytes	May enhance metformin effect; monitor for GI side effects and hypoglycaemia

Common Adverse effects

Nausea (very common initially; usually transient)
Diarrhoea
Abdominal discomfort, bloating
Flatulence
Metallic taste (dysgeusia)
Anorexia, decreased appetite
Headache

Note: GI adverse effects are usually transient (first 2–4 weeks) and can be minimized by starting at low dose, slow titration, and taking with meals. MR/XR formulations may improve GI tolerability.

Serious Adverse effects

Adverse Effect	Clinical Action
Lactic Acidosis (rare but potentially fatal; incidence ~3–10 per 100,000 patient-years)	Medical emergency — discontinue metformin immediately; symptoms include malaise, myalgia, respiratory distress, abdominal pain, hypothermia, hypotension; check arterial lactate, pH, bicarbonate; supportive care; haemodialysis may be required in severe cases
Vitamin B12 Deficiency (with long-term use; incidence 5–10% after >4 years)	Monitor serum B12 annually in long-term users; supplement if deficient; presents as macrocytic anaemia, peripheral neuropathy
Hepatotoxicity (very rare)	Monitor LFTs if symptoms of hepatic dysfunction; discontinue if significant elevation
Hypoglycaemia (rare as monotherapy; occurs with insulin/sulfonylureas)	Reduce dose of concomitant hypoglycaemic agent; patient education on recognition and management

Monitoring requirements

Timing	Parameters
Baseline	Renal function (serum creatinine, eGFR); hepatic function (LFTs); fasting blood glucose, postprandial glucose, HbA1c; vitamin B12 (if long-term use planned or risk factors for deficiency)
After initiation / dose change (1–3 months)	Glycaemic parameters (FBG, PPBG, HbA1c); renal function (eGFR); GI tolerability
Long-term (every 3–6 months)	HbA1c (every 3–6 months); eGFR (at least annually; more frequently if eGFR <60 or declining); vitamin B12 (annually if on therapy >12 months); LFTs (periodically if hepatic concerns)
Special Situations	Check renal function before and 48 hours after iodinated contrast procedures; withhold during acute illness with dehydration risk

Brands in India

mmediate-Release Tablets:

Glyciphage™ (Franco-Indian) — 250 mg, 500 mg, 850 mg, 1000 mg
Glycomet™ (USV) — 250 mg, 500 mg, 850 mg
Gluformin™ (Abbott) — 500 mg, 850 mg
Obimet™ (Corona Remedies) — 500 mg
Bigomet™ (Aristo) — 500 mg, 850 mg
Formin™ (Sanofi) — 500 mg

Modified-Release/Sustained-Release Tablets:

Glyciphage SR™ (Franco-Indian) — 500 mg, 1000 mg
Glycomet SR™ (USV) — 500 mg, 1000 mg
Gluformin XR™ (Abbott) — 500 mg, 1000 mg
Metlong™ (USV) — 500 mg SR

Fixed-Dose Combinations (Examples):

Glyciphage G™ (Metformin + Glimepiride)
Glycomet Trio™ (Metformin + Glimepiride + Pioglitazone/Voglibose)
Galvus Met™ (Metformin + Vildagliptin)
Janumet™ (Metformin + Sitagliptin)
Trajenta Duo™ (Metformin + Linagliptin)
Jardiance Met™ (Metformin + Empagliflozin)

⚠️ Note on FDCs: When using FDCs, ensure total metformin dose is calculated correctly to avoid under- or overdosing. FDCs may limit dose flexibility during titration.

Price range (INR)

500 mg IR tablet	₹0.50–₹2.00 per tablet	NLEM listed
850 mg IR tablet	₹1.00–₹3.00 per tablet	—
1000 mg IR tablet	₹1.50–₹4.00 per tablet	—
500 mg SR/XR tablet	₹1.50–₹4.00 per tablet	—
1000 mg SR/XR tablet	₹2.50–₹6.00 per tablet	—
FDCs	₹4–₹25 per tablet	Variable based on combination

Regulatory: Listed under NLEM 2022 (500 mg, 850 mg tablets); NPPA price controlled for scheduled strengths; widely available in government supply

Clinical pearls

First-line agent for Type 2 DM — Continue metformin unless contraindicated when adding other agents; proven cardiovascular benefit (UKPDS); no weight gain; no hypoglycaemia as monotherapy
GI tolerability strategy — Start low (500 mg once daily), titrate slowly (every 1–2 weeks), take with meals; if IR formulation not tolerated, switch to MR/SR/XR formulation for better GI tolerance
Sick day rules — Educate patients to temporarily withhold metformin during acute illness with dehydration risk (vomiting, diarrhoea, fever, reduced oral intake) or when undergoing procedures with contrast media; resume when eating and drinking normally and renal function stable
Contrast media protocol — Withhold 48 hours before and after iodinated contrast procedures if eGFR <60 or other AKI risk factors; confirm stable renal function before resuming
Vitamin B12 deficiency — Screen annually in long-term users (>3–4 years); higher risk in vegetarians, elderly, and those on higher doses; supplement if deficient to prevent irreversible neuropathy
PCOS and fertility — May improve ovulation rates; can be continued through conception and early pregnancy (discuss with obstetrician); transition to insulin for GDM if glycaemic targets not met

Version

RxIndia v1.0 — 29 Apr 2025

Reference

CDSCO Product Information
Indian Pharmacopoeia (IP)
National List of Essential Medicines (NLEM) 2022
API Textbook of Medicine
ICMR Guidelines for Management of Type 2 Diabetes 2018
AIIMS Drug Formulary and Treatment Protocols
IAP Paediatric Endocrinology Guidelines
IAP Adolescent PCOS Guidelines
Harrison's Principles of Internal Medicine
Goodman & Gilman's The Pharmacological Basis of Therapeutics
Indian Diabetes Prevention Programme (IDPP) Study
MiG Trial (Metformin in Gestational Diabetes)
WHO Essential Medicines List (paediatric support)

⚖️

Clinical Responsibility

This platform is designed strictly for healthcare professionals. Data provided is synthesized from authoritative pharmacological sources and clinical registries. Do not use for consumer medical decisions. Always verify critical dosing and contraindications with official institutional protocols and peer-reviewed journals.

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Parameter

Dose

Starting dose

500 mg orally once or twice daily with meals

Titration

Increase by 500 mg every 7–14 days based on glycaemic response and GI tolerability

Usual maintenance dose

1500–2000 mg/day in 2–3 divided doses with meals

Maximum dose

2550 mg/day (in divided doses)

Parameter

Dose

Starting dose

500 mg orally once daily with evening meal

Titration

Increase by 500 mg every 1–2 weeks based on glycaemic response

Usual maintenance dose

1500–2000 mg once daily with evening meal

Maximum dose

2000 mg/day (once daily)

Parameter

Dose

Starting dose

500 mg orally once daily with food

Titration

Increase by 500 mg every 1–2 weeks to improve GI tolerance

Usual maintenance dose

1500–2000 mg/day in 2–3 divided doses

Maximum dose

2550 mg/day (typically ≤2000 mg/day in practice)

Indication

Dose

Duration

Supervision

Evidence Basis

Prevention of Type 2 Diabetes in High-Risk Individuals (Prediabetes/IFG/IGT) (OFF-LABEL)

Starting: 500 mg once daily; Titration: increase to 500–1000 mg twice daily as tolerated; Maintenance: 1000–1700 mg/day

Long-term; indefinite if risk factors persist

Specialist recommended

DPP trial; Indian Diabetes Prevention Programme (IDPP) data; ICMR guidance for high-risk individuals with metabolic syndrome not responding to lifestyle alone

Gestational Diabetes Mellitus (GDM) — Alternative to Insulin (OFF-LABEL)

Starting: 500 mg once or twice daily; Titration: increase by 500 mg/week; Maintenance: 1000–2500 mg/day in divided doses

Duration of pregnancy

Specialist only (Obstetrician/Endocrinologist)

MiG trial; Indian obstetric practice; used when insulin is declined, unavailable, or as adjunct

Antipsychotic-Induced Weight Gain and Metabolic Syndrome (OFF-LABEL)

500–2000 mg/day in divided doses

Long-term as needed

Specialist only (Psychiatrist)

RCTs showing benefit in clozapine/olanzapine-induced weight gain; Indian psychiatric practice

Non-Alcoholic Fatty Liver Disease (NAFLD) with Insulin Resistance (OFF-LABEL)

1000–2000 mg/day in divided doses

Long-term

Specialist recommended (Gastroenterology/Endocrinology)

Limited evidence; may improve insulin resistance but no proven effect on liver histology; used in Indian practice for associated metabolic syndrome

Parameter

Dose

Starting dose

500 mg orally once daily with meals

Titration

Increase by 500 mg every 1–2 weeks based on glycaemic response and GI tolerability

Usual maintenance dose

1000–2000 mg/day in 2–3 divided doses

Maximum dose

2000 mg/day

Parameter

Dose

Starting dose

500 mg orally once daily with evening meal

Titration

Increase by 500 mg every 1–2 weeks

Usual maintenance dose

1000–2000 mg once daily

Maximum dose

2000 mg/day

Indication

Age

Dose

Duration

Supervision

Evidence Basis

Polycystic Ovary Syndrome (PCOS) in Adolescent Girls (OFF-LABEL)

≥12 years

Starting: 500 mg once daily; Titration: increase by 500 mg every 1–2 weeks; Maintenance: 1000–2000 mg/day in divided doses; Maximum: 2000 mg/day

≥6 months; reassess periodically

Specialist only (Paediatric Endocrinology/Adolescent Gynaecology)

IAP adolescent PCOS guidelines; Indian paediatric endocrinology practice

Obesity with Insulin Resistance (OFF-LABEL)

≥10 years

500–2000 mg/day in divided doses

Long-term with lifestyle intervention

Specialist only (Paediatric Endocrinology)

Limited evidence; used as adjunct to lifestyle modification in severe obesity with metabolic complications

eGFR (mL/min/1.73 m²)

Recommendation

≥60

No dose adjustment required

45–59

Use with caution; maximum 2000 mg/day; monitor eGFR every 3–6 months

30–44

Reduce dose; maximum 1000 mg/day; monitor eGFR every 3 months; not to be initiated if eGFR <45

<30

Contraindicated

Haemodialysis

Contraindicated

Peritoneal Dialysis

Contraindicated

Parameter

Information

Overall Safety

Limited but reassuring human data; no confirmed teratogenicity; considered acceptable when indicated

Risk

Crosses placenta; theoretical concerns about fetal effects not substantiated in clinical studies

Preferred Alternatives

Insulin is first-line for GDM and pre-existing T2DM in Indian obstetric guidelines

When Use May Be Justified

GDM when insulin is declined, unavailable, or as adjunct to insulin for insulin resistance; PCOS-related infertility (may continue through first trimester with specialist guidance)

Monitoring

Maternal blood glucose (FBG, PPBG, HbA1c); fetal growth by serial ultrasound; monitor for neonatal hypoglycaemia after delivery

Parameter

Information

Compatibility

Compatible with breastfeeding

Expected Drug Level in Milk

Very low (approximately 0.5–1% of weight-adjusted maternal dose reaches infant)

Risk to Infant

Minimal; no significant adverse effects reported in breastfed infants

Preferred Alternatives

None — metformin is preferred over sulfonylureas for glycaemic control in breastfeeding mothers with T2DM

Infant Monitoring

Feeding adequacy, weight gain (routine monitoring sufficient)

Parameter

Recommendation

Starting dose

500 mg orally once daily with food

Titration

Increase slowly (every 2 weeks); assess tolerability and renal function frequently

Maximum recommended

Based on renal function; often limited to 1500–2000 mg/day

Increased Risks

Lactic acidosis (age-associated decline in renal function); GI intolerance; vitamin B12 deficiency

Additional Precautions

Assess eGFR before initiation and at least every 3–6 months; avoid in frail elderly with multiple comorbidities predisposing to lactic acidosis; use MR/XR formulations to improve GI tolerability; educate on sick day rules

Interacting Drug

Mechanism

Effect

Management

Iodinated Contrast Media

Contrast-induced nephropathy may impair metformin excretion

Increased risk of lactic acidosis

Withhold metformin 48 hours before and after contrast administration if eGFR <60 or other risk factors; resume only after confirming stable renal function

Excessive Alcohol

Alcohol increases lactate production and impairs gluconeogenesis

Significantly increased risk of lactic acidosis; risk of hypoglycaemia

Avoid excessive/binge alcohol consumption; moderate intake acceptable with caution

Cimetidine

Competes for renal tubular secretion

Increased metformin plasma levels (up to 50%)

Avoid combination or monitor closely; consider alternative H2 blocker (ranitidine, famotidine) or PPI

Dolutegravir

Inhibits renal tubular secretion of metformin (OCT2/MATE inhibition)

Increased metformin levels

Monitor for metformin adverse effects; consider dose reduction if GI intolerance develops

Interacting Drug

Effect

Management

ACE Inhibitors / ARBs

May impair renal function; potential for acute kidney injury

Monitor eGFR; adjust metformin dose if renal function declines

Loop Diuretics / Thiazides

Risk of dehydration and prerenal AKI; diuretics may worsen glucose tolerance

Monitor hydration status, renal function, and glycaemic control

NSAIDs

Risk of acute kidney injury, especially in dehydrated patients

Use with caution; ensure adequate hydration; monitor renal function

Corticosteroids (systemic)

Oppose glycaemic effects of metformin; may cause hyperglycaemia

Monitor blood glucose; may need temporary increase in metformin dose or addition of other antidiabetic agents

Beta-blockers

May mask hypoglycaemia symptoms (relevant when metformin combined with insulin/sulfonylureas)

Counsel patient on hypoglycaemia awareness; less relevant with metformin monotherapy

Carbonic Anhydrase Inhibitors (topiramate, acetazolamide)

May increase risk of lactic acidosis

Use with caution; monitor for acidosis symptoms

Vancomycin

Potential for additive nephrotoxicity

Monitor renal function closely

Rifampicin

Induces OCT1 transporter; may increase metformin uptake into hepatocytes

May enhance metformin effect; monitor for GI side effects and hypoglycaemia

Adverse Effect

Clinical Action

Lactic Acidosis (rare but potentially fatal; incidence ~3–10 per 100,000 patient-years)

Medical emergency — discontinue metformin immediately; symptoms include malaise, myalgia, respiratory distress, abdominal pain, hypothermia, hypotension; check arterial lactate, pH, bicarbonate; supportive care; haemodialysis may be required in severe cases

Vitamin B12 Deficiency (with long-term use; incidence 5–10% after >4 years)

Monitor serum B12 annually in long-term users; supplement if deficient; presents as macrocytic anaemia, peripheral neuropathy

Hepatotoxicity (very rare)

Monitor LFTs if symptoms of hepatic dysfunction; discontinue if significant elevation

Hypoglycaemia (rare as monotherapy; occurs with insulin/sulfonylureas)

Reduce dose of concomitant hypoglycaemic agent; patient education on recognition and management

Timing

Parameters

Baseline

Renal function (serum creatinine, eGFR); hepatic function (LFTs); fasting blood glucose, postprandial glucose, HbA1c; vitamin B12 (if long-term use planned or risk factors for deficiency)

After initiation / dose change (1–3 months)

Glycaemic parameters (FBG, PPBG, HbA1c); renal function (eGFR); GI tolerability

Long-term (every 3–6 months)

HbA1c (every 3–6 months); eGFR (at least annually; more frequently if eGFR <60 or declining); vitamin B12 (annually if on therapy >12 months); LFTs (periodically if hepatic concerns)

Special Situations

Check renal function before and 48 hours after iodinated contrast procedures; withhold during acute illness with dehydration risk

500 mg IR tablet

₹0.50–₹2.00 per tablet

NLEM listed

850 mg IR tablet

₹1.00–₹3.00 per tablet

—

1000 mg IR tablet

₹1.50–₹4.00 per tablet

—

500 mg SR/XR tablet

₹1.50–₹4.00 per tablet

—

1000 mg SR/XR tablet

₹2.50–₹6.00 per tablet

—

FDCs

₹4–₹25 per tablet

Variable based on combination