Cardiovascular Drugs USMLE Step 1 Practice Question
A 65-year-old woman with heart failure on lisinopril and furosemide is started on spironolactone. Three weeks later, she presents with weakness and palpitations. Vital signs: BP 98/62 mmHg, HR 108 bpm, RR 16, temp 37°C. Labs reveal K+ 6.5 mEq/L, creatinine 1.8 mg/dL (baseline 1.0), normal magnesium. ECG shows peaked T waves. Which mechanism of spironolactone most directly explains this complication?
Answer choices
- AAldosterone antagonism reducing potassium excretion and sodium reabsorption in the distal tubuleCorrect answer
- BSpironolactone directly activates potassium channels in the collecting duct
- CInhibition of proximal tubule potassium reabsorption
- DIncreased renal blood flow promoting potassium filtration
- ECompetitive inhibition of the Na-K-ATPase pump
- FInhibition of potassium-sparing diuretic metabolism in the liver leading to systemic accumulation
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