CNS Pharmacology USMLE Step 1 Practice Question

A 34-year-old man presents to a base camp medical station after ascending rapidly from 1,400 m to 4,200 m over 18 hours during a Himalayan trekking expedition. He reports a throbbing bifrontal headache, nausea, generalized fatigue, and lightheadedness that began approximately 6 hours after arrival. He has no significant past medical history and takes no regular medications. On examination, his temperature is 37.1°C, blood pressure is 138/84 mmHg, heart rate is 102 beats/min, respiratory rate is 18 breaths/min, and oxygen saturation is 88% on room air. Arterial blood gas analysis reveals a pH of 7.45 and a mildly elevated bicarbonate of 26 mEq/L, consistent with early respiratory alkalosis. The expedition physician initiates a medication that inhibits carbonic anhydrase in the proximal tubule, causing bicarbonate diuresis and a mild compensatory metabolic acidosis that reflexively stimulates ventilation and improves oxygenation. Which of the following drugs was most likely prescribed?