Metformin

Class
Hypoglycemic agents
Subclass
Biguanides
Substance name
metFORMIN
Brand names
Riomet®
Common formulations
Tablet, Solution
See also
Metformin ER (Fortamet®, Glumetza®)
Contained in
Alogliptin / metformin (Kazano®)
Glyburide / metformin (Glucovance®)
Linagliptin / metformin (Jentadueto®)
Sitagliptin / metformin (Janumet®, Zituvimet®)
Dosage and administration
Adults patients
Treatment
Diabetes mellitus type 2
•
Start at: 500 mg PO BID
•
Maintenance: 1,000-2,550 mg PO daily, in 2-3 divided doses
Taken with meals. Titrate in 500 mg increments weekly.
Alternative
•
Start at: 850 mg PO daily
•
Maintenance: 850-2,550 mg PO daily, in 1-3 divided doses
Taken with meals. Titrate in 500 mg increments weekly.
Antipsychotic-induced weight gain • Off-label
•
Start at: 250-500 mg PO BID
•
Maintenance: 1,000-2,000 mg PO daily, in 2-3 divided doses
Gestational diabetes • Off-label
•
Start at: 500 mg PO daily
•
Maintenance: 2,000-2,500 mg PO daily, in 2-3 divided doses ; continue 850 mg PO BID after pregnancy
Taken with meals.
PCOS • Off-label
•
1,500-2,000 mg PO daily, in 2-3 divided doses
Alternative
•
Start at: 250-500 mg PO daily
•
Maintenance: 850 mg PO BID
Prediabetes • Off-label
•
850 mg PO BID
Prevention
Antipsychotic-induced weight gain • Off-label
•
500-2,000 mg PO daily, in 1-3 divided doses
Titrate weekly to 1,000 mg, then every two weeks thereafter as tolerated.
Ovarian hyperstimulation syndrome with PCOS, during IVF • Off-label
•
500 mg PO TID
Alternative
•
850 mg PO BID
Indications for use
Labeled indications
Adults
•
Treatment of diabetes mellitus type 2
Off-label indications
Adults
•
Treatment of antipsychotic-induced weight gain
•
Treatment of gestational diabetes
•
Treatment of PCOS
•
Treatment of prediabetes
•
Prevention of antipsychotic-induced weight gain
•
Prevention of ovarian hyperstimulation syndrome with PCOS, in patients undergoing IVF
Safety risks
Boxed warnings
Lactic acidosis
•
Use extreme caution in patients with renal impairment, concomitant use of certain drugs (carbonic anhydrase inhibitors, such as topiramate), age ≥ 65 years, undergoing a radiological evaluation with contrast, surgery, and other procedures, hypoxic states (such as acute congestive HF), excessive alcohol intake, and hepatic impairment. Assess eGFR before initiating metformin and monitor annually or more frequent in patients at risk of renal impairment.
Contraindications
Hypersensitivity to metformin or its components
Metabolic acidosis
•
Do not use metformin in patients with acute or chronic metabolic acidosis, including diabetic ketoacidosis, with or without coma.
Use of iodine-containing contrast medium
•
Discontinue metformin before iodinated contrast imaging in patients with an eGFR 30-60 mL/min/1.73 m², history of liver disease, alcohol use disorder, or HF, or in patients who will be administered intra-arterial iodinated contrast. Reassess eGFR 48 hours after the imaging and restart metformin if renal function is stable.
Warnings and precautions
Decreased blood glucose
•
Use caution in patients taking insulin or insulin secretagogues. Consider reducing the insulin or insulin secretagogue dose.
Vitamin B12 deficiency
•
Maintain a high level of suspicion, as metformin has been associated with an increased risk of vitamin B12 deficiency. Assess hematologic parameters annually and vitamin B12 every 2-3 years.
Specific populations
Renal impairment
eGFR ≥ 45 mL/min/1.73 m²
•
Use acceptable. No dose adjustment required. Monitor renal function. Monitor for lactic acidosis. Discontinue before iodinated contrast imaging in patients with an eGFR 45-60 mL/min/1.73 m².
eGFR 30-45 mL/min/1.73 m²
•
Avoid use. Monitor renal function. Monitor for lactic acidosis. Assess the benefit/risk of continuing therapy in patients initiated on metformin at higher eGFR rates. Consider initiating metformin at 500 mg once daily, then titrating to 500 mg twice daily if well-tolerated, while closely monitoring renal function. Consider maintaining treatment at a decreased dosage for ongoing management, and increasing up to a maximum of 500 mg twice daily with close monitoring of kidney function. Discontinue metformin before iodinated contrast imaging.
eGFR < 30 mL/min/1.73 m²
•
Do not use.
Renal replacement therapy
Continuous renal replacement
•
Do not use.
Intermittent hemodialysis
•
Do not use.
Peritoneal dialysis
•
Do not use.
Hepatic impairment
Any severity
•
Avoid use.
Substantial chronic alcohol consumption
•
Avoid use.
Pregnancy and breastfeeding
Pregnancy
All trimesters • Australia Category: C
•
Use only if benefits outweigh potential risks. Insulin is the preferred first-line treatment for diabetes in pregnancy.
•
The ACOG guidelines suggest metformin as a second-line choice in patients declining insulin or are unable to safely administer insulin. The American Diabetes Association guidelines recommend discontinuing metformin, when used to treat PCOS and induce ovulation, by the end of the first trimester.
Breastfeeding
Use only if benefits outweigh potential risks.
•
The Endocrine Society guidelines recommend that breastfeeding patients with overt diabetes, who have successfully used metformin during pregnancy, continue to use metformin during breastfeeding if necessary.
Low levels in breastfed infants (5-25%).
Adverse reactions
Very common > 10%
•
Diarrhea, flatulence, nausea, vomiting
Common 1-10%
•
↓ blood glucose, change in bowel habits, hyperhidrosis, abdominal discomfort, asthenia, change in taste, chest discomfort, chills, dyspepsia, headache, myalgia, lightheadedness, dyspnea, palpitations, flu-like symptoms, skin flushing, skin rash, vitamin B12 deficiency
Uncommon < 1%
•
Lactic acidosis, megaloblastic anemia, metabolic acidosis
Unknown frequency
•
Drug-induced liver injury, lichen planus, encephalopathy, ↑ liver enzymes, dizziness, loss of appetite, weight loss
Interactions
Drug(s)
Check Interactions
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