Metformin
GLUCOPHAGE
What it isBiguanide that suppresses hepatic gluconeogenesis and improves insulin sensitivity; first-line for type 2 diabetes.
Why this oneWeight-neutral to weight-losing, causes no hypoglycemia as monotherapy, and carries the longest safety record of any oral agent.
What limits itRenally cleared: avoid below eGFR 30 and hold around iodinated contrast. GI intolerance is the usual reason it fails; long-term use depletes B12.
FDA-approved for
- type 2 diabetes (1994)
Off-label
- PCOS
- antipsychotic weight gain
- prediabetes
FDA label
Read the full label on DailyMed ↗
| FDA dosing | Population | Start | Target | Max |
|---|---|---|---|---|
| Type 2 diabetes mellitus | Adults | 500 mg BID or 850 mg QD (with meals) | Titrate to glycemic control | 2550 mg/day divided |
| Type 2 diabetes mellitus | Pediatric 10–16 yr | 500 mg BID (with meals) | Titrate to glycemic control | 2000 mg/day divided BID |
Titration Increase by 500 mg weekly or 850 mg every 2 weeks
Renal Contraindicated if eGFR <30; do not initiate if eGFR 30–45; reassess if eGFR falls <45; check eGFR before and ≥annually
Hepatic Avoid use in hepatic impairment (lactic acidosis risk)
Instructions
- Take with meals
- Doses above 2000 mg may be better tolerated given 3 times a day with meals
- Discontinue at/before iodinated contrast procedures in at-risk patients; re-evaluate eGFR 48h after and restart if stable
- Temporarily discontinue during surgery/procedures with restricted food and fluids
Contraindications
- Severe renal impairment (eGFR <30 mL/min/1.73m²)
- Acute or chronic metabolic acidosis, including diabetic ketoacidosis
Cautions
- Lactic acidosis (see boxed warning)
- Vitamin B12 deficiency; monitor hematologic parameters annually and B12 every 2–3 years
- Hypoglycemia when combined with insulin or insulin secretagogues
Adverse reactions
- Diarrhea
- Nausea/vomiting
- Flatulence
- Asthenia
- Indigestion
- Abdominal discomfort
- Headache
Pregnancy Limited data insufficient to establish risk; published studies show no clear association with birth defects or miscarriage
Lactation Present in human milk; insufficient data on effects on infant or milk production
⚠ BOXED WARNING
- Lactic acidosis
Cost, est. cash$5–$150/month
Generic entry2002
Classes and tags
Clinical profile
Legacy pregnancy categoryB
Defining liabilityGI intolerance and vitamin B12 deficiency; severe renal/hypoxic illness can precipitate lactic acidosis.
Mechanism of action: Metformin ballicule
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