Antimicrobials USMLE Step 1 Practice Question
A 45-year-old man with chronic kidney disease secondary to long-standing hypertension presents with fever, dysuria, and flank pain. His baseline eGFR is 25 mL/min and serum creatinine is 2.8 mg/dL. He is started on gentamicin 2 mg/kg IV every 8 hours for a complicated urinary tract infection after urine culture grows gentamicin-sensitive Escherichia coli. His temperature is 38.6°C, blood pressure 148/92 mmHg, and heart rate 98 bpm. On day 3 of therapy, repeat labs show serum creatinine risen to 4.2 mg/dL, urine output has decreased to 400 mL over 24 hours, and urinalysis reveals granular casts and tubular epithelial cell casts. Serum drug levels are noted to be elevated. Which of the following best describes the mechanism of this adverse effect?
Answer choices
- AAcute interstitial nephritis from drug hypersensitivity
- BGlomerular filtration barrier disruption by immune complexes
- CProximal tubular toxicity from aminoglycoside accumulationCorrect answer
- DPrerenal azotemia from volume depletion
- ECompetitive inhibition of renal filtration by gentamicin
- FAcute tubular necrosis from sepsis-induced ischemic injury
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