Educational use only. Drug cards are AI-assisted study material for NCLEX preparation.
Mechanism of action
Reduces hepatic gluconeogenesis (the main effect), enhances peripheral insulin sensitivity, and decreases intestinal glucose absorption. Does NOT cause hypoglycemia as monotherapy because it does not stimulate insulin release. First-line oral agent for type 2 diabetes and used for prediabetes and PCOS.
Adverse effects
Life-threatening / NCLEX-tested
- Lactic acidosis — rare but life-threatening; risk rises with renal impairment, contrast media, hypoxia, sepsis, alcohol abuse, severe heart failure
- Vitamin B12 deficiency with long-term use → peripheral neuropathy, anemia
- Severe GI intolerance at start of therapy
Side effects
Common — what to teach
- GI upset — diarrhea, nausea, abdominal cramps, metallic taste (very common; usually improves with extended-release formulation and gradual titration)
- Mild bloating
- Loss of appetite (usually transient)
- Mild weight loss (clinical advantage over many other diabetes agents)
- Mild headache
Food & drug interactions
IV iodinated contrast — hold metformin AT THE TIME OF the procedure for patients with eGFR < 30 or AKI; for stable normal renal function, current ACR guidance does not require routine holding, but check institutional protocol. Alcohol increases lactic acidosis risk. Cimetidine raises levels. Carbonic anhydrase inhibitors (topiramate, acetazolamide) compound acidosis risk.
Nursing implications
Assessment, monitoring, patient teaching
- Take WITH meals to limit GI side effects; titrate dose gradually (start 500 mg with the largest meal, increase weekly)
- Hold AT THE TIME OF iodinated contrast procedure if eGFR < 30 or any AKI; restart 48 hours after, after re-checking creatinine
- Monitor renal function (eGFR/creatinine) at baseline and at least yearly; metformin is contraindicated when eGFR < 30, used cautiously between 30 and 45
- Counsel: report unexplained muscle pain, deep abdominal pain, hyperventilation, or unusual fatigue — possible lactic acidosis
- Recommend B12 level periodically with long-term use (5+ years), and if neuropathy emerges
- Avoid heavy alcohol use
- Hold during acute illness with vomiting/diarrhea/poor oral intake or sepsis (sick-day rule)
When to hold / contraindications
- eGFR < 30 mL/min (contraindicated)
- Acute kidney injury or rising creatinine
- Iodinated contrast in patients with eGFR < 30 or AKI
- Acute illness with significant volume loss or sepsis (sick-day rule)
- Severe heart failure decompensation, severe hepatic impairment, or ongoing alcohol abuse
- Active or suspected lactic acidosis
Memory anchor
Metformin = "first-line, no hypoglycemia, take with meals." Hold for contrast in renal impairment; sick-day rule in any acute illness; B12 in long-term use.
Practice Metformin questions
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