Metformin

Administration

• Type: Diabetes medication
• Dosage Forms: 500, 850, 1000; ER 500, 750, 1000
• Routes of Administration: PO
• Common Trade Names: Fortamet, Glucophage, Glumetza, Riomet

Adult Dosing

Diabetes Mellitus type 2

• Take with meals
• Hold 48 hours for iodinated contrast

Immediate Release

• 850-1000mg PO bid
• Start 500mg bid or 850mg qd
• Increase 500mg qwk or 850mg q2wk
• Max 2550mg/day

Extended Release

• 1000-2000mg PO qd
• Start 500mg qd
  • Increase 500mg qwk
• Alt dosing; 1000mg bid
  • Add 500mg immediate release for inadequate response
• Do not crush or chew

Polycystic Ovarian Syndrome

• Take with meals
• Hold for iodinated contrast

Immediate Release

• 500mg tid
• Alt dosing; 850-1000mg bid
• Increase as needed
• Max 2550mg/day

Extended Release

• 1500-2000mg qd
• Do not crush or chew
• Max 2000mg/day

Pediatric Dosing

• Take with meals
• Hold for iodinated contrast
• Children aged 10-18 years of age

Diabetes Mellitus type 2

• 500-1000mg bid
• Start 500mg qd
• Increase 500mg/day every 1-2 weeks
• Max 2000mg/day

Special Populations

• Pregnancy Rating: B
• Lactation risk: Probably safe

Renal Dosing

• Adult: Contraindicated Cr>1.4 in females and Cr>1.5 in med
• Pediatric: Contraindicated Cr>1.4 in females and Cr>1.5 in med

Hepatic Dosing

• Adult: Avoid with hepatic impairment
• Pediatric: Avoid with hepatic impairment

Contraindications

• Allergy to class/drug
• Creatinine >1.4 female or >1.5 male
• Metabolic acidosis
• DKA
• Lactic acidosis
• Iodinated contrast
• Hypoxemia
• Dehydration
• Sepsis
• Surgery
• Hepatic impairment

Caution

• CHF
• Elderly
• Alcohol abuse
• Hypoglycemia risk

Adverse Reactions

Serious

• Metformin-associated lactic acidosis
• Megaloblastic anemia

Common

• Diarrhea
• nausea and vomiting
• Flatulence
• Indigestion
• Abdominal discomfort
• Anorexia
• Headache
• Rash
• Ovulation reduction

Pharmacology

• Half-life: 6 hours in plasma and 17 hours in blood
• Metabolism: CYP450
• Excretion: Urine

Mechanism of Action

• Decreases hepatic glucose production and intestinal absorption
• Increases insulin sensitivity

See Also

• Metformin-associated lactic acidosis
• Diabetes medications

References

Epocrates