Cardiovascular Drugs USMLE Step 1 Practice Question
A 70-year-old man with heart failure (EF 35%) and Stage 3b chronic kidney disease presents with weakness and palpitations. Vitals: BP 128/76 mmHg, HR 92/min, RR 16/min, Temp 37°C, SpO2 98% on room air. One month after starting spironolactone, labs show serum potassium 6.2 mEq/L (normal 3.5-5.0), creatinine 2.1 mg/dL (baseline 1.8), and normal magnesium. No concurrent ACE inhibitor use is documented. Which mechanism best explains the hyperkalemia?
Answer choices
- ADisplacement of potassium from intracellular stores to plasma
- BIncreased proximal tubule reabsorption of filtered potassium
- CDirect inhibition of Na-K-ATPase pump activity
- DAldosterone antagonism reducing urinary potassium excretion in collecting ductCorrect answer
- EEnhanced glomerular filtration of potassium-albumin complexes
- FDecreased aldosterone-independent potassium secretion in the distal convoluted tubule
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