What major adverse effect of metformin requires monitoring during illness or dehydration?

• A. Lactic acidosis risk; risk increases with renal impairment or dehydration; hold metformin during acute illness or before contrast imaging.
• B. Hypoglycemia and weight gain.
• C. Increased blood pressure.
• D. Hair loss.

Answer: (A)

Lactic acidosis risk from metformin is what you watch for during illness or dehydration. When you’re dehydrated or have an acute illness, kidney function can worsen and metformin can accumulate in the body. This slows lactate clearance and can increase lactate production, tipping you toward lactic acidosis. Because contrast imaging or dehydration can further stress the kidneys, holding metformin in these situations helps prevent this serious complication.

Other effects like hypoglycemia with weight gain, blood pressure changes, or hair loss aren’t the major concern in this context; metformin more commonly causes GI upset and may be weight-neutral or lead to modest weight loss, but not this acute, life-threatening risk.