Cardiovascular Drugs USMLE Step 1 Practice Question
A 55-year-old man with hypertension started on hydrochlorothiazide 25 mg daily presents with muscle weakness and fatigue. Vital signs: BP 138/82 mmHg, HR 92 bpm, RR 16/min, Temp 37°C, SpO2 98% on room air. Laboratory studies show serum potassium 3.0 mEq/L (normal 3.5–5.0), fasting glucose 248 mg/dL, arterial pH 7.48, and normal urinary protein. Which mechanism best explains the thiazide-induced hypokalemia?
Answer choices
- ADecreased reabsorption of potassium in the proximal convoluted tubule
- BAldosterone antagonism leading to potassium retention failure
- CDirect potassium wasting through inhibition of H+ secretion in the distal tubule
- DDirect inhibition of Na+/K+-ATPase pump in the collecting duct
- EIncreased urinary potassium loss due to enhanced distal tubular secretion via increased sodium deliveryCorrect answer
- FThiazide-induced hypomagnesemia impairing renal potassium conservation and causing refractory hypokalemia
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