Acetazolamide is a carbonic anhydrase inhibitor used in altitude sickness. The mechanism by which it reduces altitude sickness is:

• A It reduces pulmonary vasoconstriction at altitude by blocking hypoxia-induced vasoconstriction through cAMP elevation
• B It acts as a diuretic, reducing plasma volume and decreasing cardiac output at altitude
• C It causes respiratory stimulation by inducing metabolic acidosis that drives hyperventilation and raises PaO2 ✓
• D It stimulates erythropoietin release, increasing red cell mass and oxygen-carrying capacity

Explanation

Acetazolamide inhibits carbonic anhydrase in the renal proximal tubule, reducing HCO3- reabsorption and causing a mild metabolic (hyperchloraemic) acidosis. This systemic acidosis stimulates peripheral chemoreceptors (carotid bodies), inducing hyperventilation and raising PaO2 while lowering PaCO2 — essentially accelerating the ventilatory acclimatisation that normally takes days. The improved PaO2 reduces cerebral and pulmonary altitude-related symptoms. Additionally, it reduces CSF production, which may help altitude-related cerebral oedema.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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