What safety concern is associated with metformin, particularly in renal impairment or dehydration?

• A. Hypoglycemia
• B. GI upset
• C. Weight gain
• D. Lactic acidosis

Answer: (D)

Metformin carries a risk of lactic acidosis, especially when its clearance is reduced by renal impairment or when dehydration and hypoperfusion occur. Metformin can shift cellular energy metabolism toward increased lactate production, and if the kidneys can’t clear metformin or lactate effectively, lactate can accumulate, leading to lactic acidosis. This is a rare but potentially life-threatening complication, so metformin should be used with caution in patients with kidney dysfunction and paused during dehydration or acute illnesses that predispose to hypoxia or renal injury. In contrast, hypoglycemia is not a common direct risk with metformin alone, and while GI upset and weight loss can occur, the serious safety concern in renal impairment or dehydration is lactic acidosis.