Metformin on the NCLEX
Metformin: first-line for type 2 diabetes, lactic acidosis risk, the contrast-dye hold, GI effects, B12.
Metformin is first-line for type 2 diabetes. The NCLEX tests two holds and one rare emergency more than anything else about it.
Why it is first-line
Decreases hepatic glucose production and improves insulin sensitivity. Does not cause hypoglycemia by itself and does not cause weight gain, which separates it from sulfonylureas and insulin in exam questions.
Lactic acidosis
Rare but lethal, and the NCLEX's favorite metformin fact. Risk climbs when the drug accumulates or lactate rises: renal impairment, acute illness with hypoperfusion, heavy alcohol use, liver disease. Report muscle pain, unusual fatigue, difficulty breathing, or GI distress that feels different from the usual startup symptoms. Contraindicated when eGFR is below 30.
The contrast-dye hold
Iodinated contrast can hit the kidneys; if metformin is still on board when that happens, it accumulates. The tested rule: hold metformin at the time of the contrast study and for 48 hours after, and restart only after renal function is rechecked. Same logic around major surgery.
GI effects
Diarrhea, nausea, and metallic taste are the common startup complaints and the top reason patients quit. Teaching that fixes it: take with food, start low with gradual titration, and ask about extended-release, which is gentler. Symptoms usually fade over weeks.
B12 deficiency
Long-term metformin impairs B12 absorption. Suspect it when a stable patient develops neuropathy symptoms or a macrocytic anemia; the sneaky exam version looks like worsening diabetic neuropathy that is actually B12. Periodic B12 levels are reasonable on long-term therapy.
Frequently asked
Patient scheduled for a CT with contrast takes metformin. What do you do?
Hold the metformin, confirm the order, and expect a renal function check before it restarts about 48 hours later.
Does metformin cause hypoglycemia?
Not by itself. Combined with insulin or a sulfonylurea, the combination can.
Which lab findings make you question a metformin order?
eGFR below 30 contraindicates it. Also flag acute kidney injury, severe liver disease, or a rising lactate.
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