A researcher measures creatinine clearance in healthy volunteers and compares it with simultaneously measured inulin clearance. The creatinine clearance consistently reads about 10 to 20 percent higher than inulin clearance. Administration of which drug would abolish this discrepancy?
- A Furosemide
- C Spironolactone
- B Cimetidine ✓
- D Acetazolamide
Correct answer: B. Cimetidine
Explanation
Creatinine clearance overestimates GFR because creatinine is secreted by the proximal tubule through the organic cation transport system. Cimetidine competitively blocks this cationic secretion, eliminating the excess clearance and bringing creatinine clearance down to the true GFR measured by inulin. Furosemide and acetazolamide alter tubular fluid flow and bicarbonate handling respectively, but neither touches cationic secretion.
Reference: Ganong's Review of Medical Physiology, 26th ed.
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