Autonomic Pharmacology USMLE Step 1 Practice Question
A 55-year-old man with a 10-year history of hypertension presents to clinic for follow-up. His blood pressure has been well controlled on lisinopril 10 mg daily (current BP 128/82 mmHg). His primary care physician adds clonidine 0.1 mg twice daily for additional blood pressure control. Two weeks later, the patient reports fatigue, generalized weakness, and mild dyspnea on exertion. Vital signs: BP 124/78 mmHg, HR 54/min, RR 16/min, temperature 37.2°C. Laboratory studies show: serum creatinine 2.3 mg/dL (baseline 0.9 mg/dL), potassium 6.9 mEq/L, BUN 48 mg/dL, urinalysis with no proteinuria or hematuria, and urine output 1.2 L/24 hours. Renal ultrasound shows no obstruction. Which of the following best explains the pathophysiologic mechanism of acute kidney injury in this patient?
Answer choices
- AAfferent arteriolar vasoconstriction reducing intraglomerular hydrostatic pressureCorrect answer
- BEfferent arteriolar vasodilation decreasing glomerular filtration pressure
- CImmune-mediated acute interstitial nephritis triggered by clonidine hypersensitivity
- DDirect proximal tubule cytotoxicity from clonidine metabolites
- EAcute volume depletion and prerenal azotemia from excessive sodium and water loss
- FIncreased glomerular basement membrane permeability with massive proteinuria
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