A patient on metformin 2 g/day requires an iodinated contrast CT. Which approach is evidence-based regarding metformin management?

• A Stop metformin 48 hours before and restart 48 hours after, in all patients regardless of renal function
• B Continue metformin without interruption as modern contrast agents are safe
• C Switch to insulin for 1 week before and after the procedure
• D Stop metformin at the time of contrast administration (or day before) and restart only after 48 hours if renal function remains stable, only in patients with eGFR <60 mL/min/1.73m² ✓

Explanation

Current ACR and ESUR guidelines recommend withholding metformin at the time of or 48 hours before iodinated contrast only in patients with eGFR <60 mL/min/1.73m², with restart after 48 hours once renal function is confirmed stable. The rationale is that contrast may cause acute kidney injury in this population, reducing metformin clearance and precipitating lactic acidosis (metformin inhibits hepatic mitochondrial complex I, reducing lactate clearance). In patients with eGFR ≥60, contrast can be given without withholding metformin.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.