A trekker develops headache, nausea, and insomnia 18 hours after arriving at 3800 m. He is treated with acetazolamide, which improves his symptoms. The therapeutic effect of this drug at altitude is best explained by:

• A Direct pulmonary vasodilation reducing hypoxic vasoconstriction
• B Renal bicarbonate loss producing metabolic acidosis that stimulates ventilation ✓
• C Inhibition of erythropoietin release, lowering hematocrit
• D Enhanced renal bicarbonate reabsorption, correcting alkalosis

Explanation

Acetazolamide inhibits carbonic anhydrase in the proximal tubule, causing bicarbonate diuresis and a mild metabolic acidosis. This acidosis offsets the respiratory alkalosis of altitude hyperventilation and provides a stronger stimulus to the peripheral chemoreceptors, increasing ventilation and arterial PO2. It does not dilate pulmonary vessels or affect erythropoietin secretion, and it reduces rather than enhances bicarbonate reabsorption.

Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.

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Written and medically reviewed by the StethoPrep medical team.