Antimicrobials USMLE Step 1 Practice Question
A 68-year-old man with stage 4 chronic kidney disease (baseline creatinine clearance 22 mL/min) presents with dysuria, urinary frequency, and suprapubic pain. Urinalysis shows pyuria and bacteriuria; urine culture grows E. coli. He is initiated on gentamicin 5 mg/kg intravenously once daily for presumed urosepsis. After 3 days of treatment, his serum creatinine increases from 2.6 to 4.1 mg/dL, and urine output decreases from 800 mL/day to 350 mL/day. Urinalysis now reveals muddy brown casts and epithelial cell casts. His vital signs remain stable (BP 136/80, HR 88, RR 14, temperature 37.1°C), and he denies fever, rash, or new flank pain. Which of the following best explains the mechanism of renal injury in this patient?
Answer choices
- AGentamicin-induced membranoproliferative glomerulonephritis causing immune complex deposition
- BAcute interstitial nephritis from drug hypersensitivity with eosinophiluria and fever
- CAminoglycoside accumulation in proximal tubule cells with inhibition of protein synthesis and cell deathCorrect answer
- DCrystalline nephropathy from precipitation of gentamicin metabolites within the distal convoluted tubule
- EDirect glomerular capillary injury from high serum gentamicin levels causing proteinuria
- FPrerenal azotemia from gentamicin-induced vasoconstriction of the afferent arteriole
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