Acetazolamide is used as prophylaxis for high-altitude cerebral/pulmonary oedema. The mechanism enabling altitude acclimatisation is:

• A Inhibition of carbonic anhydrase in erythrocytes causing a right shift of the oxygen dissociation curve
• B Inhibition of carbonic anhydrase in the proximal tubule causing bicarbonate wasting, reducing plasma pH and stimulating ventilation ✓
• C Blockade of aldosterone receptors in the collecting duct, preventing altitude-induced sodium retention
• D Inhibition of carbonic anhydrase in the choroid plexus, reducing CSF production and intracranial pressure

Explanation

At high altitude, hypoxic ventilatory response causes hyperventilation, which lowers PCO2 and raises pH (respiratory alkalosis). This alkalosis dampens the ventilatory drive (Hering-Breuer alkaline inhibition). Acetazolamide inhibits proximal tubular carbonic anhydrase, impairing HCO3- reabsorption; the resulting metabolic acidosis (bicarbonate wasting) counteracts the respiratory alkalosis and maintains ventilatory drive, improving oxygenation. The choroid plexus CA inhibition (reducing ICP) is a secondary benefit in altitude cerebral oedema.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.