Which medication is listed as a cause of normal anion gap metabolic acidosis (HARDASS)?

• A. Acetazolamide
• B. Insulin
• C. Furosemide
• D. Bicarbonate

Answer: (A)

This question tests understanding of normal anion gap (hyperchloremic) metabolic acidosis, which happens when bicarbonate is lost or cannot be reabsorbed and chloride rises to maintain electroneutrality. A classic drug cause is acetazolamide, a carbonic anhydrase inhibitor in the proximal tubule. By blocking carbonic anhydrase, bicarbonate reabsorption is reduced, so bicarbonate is lost in urine and serum bicarbonate falls, producing metabolic acidosis with a normal anion gap.

Insulin-related acidosis (as in diabetic ketoacidosis or lactic acidosis) typically yields an increased anion gap, not a normal one, so it doesn’t fit this pattern. Furosemide more commonly causes metabolic alkalosis with volume contraction rather than hyperchloremic acidosis. Administering bicarbonate would raise bicarbonate levels, not cause the acidosis in question.