A type 2 diabetic patient with CKD (eGFR 28 mL/min/1.73m²) is on metformin. Which of the following best describes the risk and the threshold at which metformin should be discontinued?

• A Risk of hyperosmolar hyperglycemic state; discontinue at eGFR < 60
• B Risk of lactic acidosis due to metformin accumulation; discontinue at eGFR < 30 ✓
• C Risk of nephrogenic diabetes insipidus; discontinue at eGFR < 45
• D Risk of hypoglycemia due to reduced renal clearance of active metabolite; discontinue at eGFR < 40

Explanation

Metformin is renally excreted unchanged and accumulates in renal impairment. Accumulation inhibits mitochondrial complex I, impairing hepatic lactate clearance and causing lactic acidosis (type B) — a rare but life-threatening complication. Current FDA guidance permits metformin use when eGFR ≥30 mL/min (with dose reduction at 30-45), and contraindicates it at eGFR <30. Initiating new metformin at eGFR 30-45 is not recommended. Metformin does not cause hypoglycemia by itself as it does not stimulate insulin secretion.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.