A 65-year-old man is hospitalized for an ischemic, nonhealing right lower extremity ulcer with associated biopsy-proven osteomyelitis. On hospital day 1, he was started on cefazolin and underwent angiography and stenting of the iliac artery using a low osmolar contrast agent. On day 2, he became febrile and was switched to vancomycin and gentamicin based on culture sensitivity data. On day 3, his fever resolved and his serum creatinine was at baseline (1.5 mg/dL [132.6 µmol/L]). On day 10, his serum creatinine increased to 3.0 mg/dL (265.2 µmol/L) with a urine output of 0.5 mL/kg/h. Medical history is notable for type 2 diabetes mellitus, hypertension, dyslipidemia, coronary artery disease, and chronic kidney disease. Medications are rosuvastatin, amlodipine, carvedilol, aspirin, insulin, vancomycin, and gentamicin.
On physical examination, blood pressure is 150/78 mm Hg, and pulse rate is 72/min. There is no rash. The lower extremities have decreased peripheral pulses. The right foot has a 1-cm clean-appearing ulcer on the tip of the second toe. The remainder of the physical examination is normal.
Hemoglobin | 11.2 g/dL (112 g/L) |
Leukocyte count | 8500/µL (8.5 × 109/L) with 58% polymorphonuclear leukocytes, 20% lymphocytes, 3% eosinophils |
Creatinine | 3.0 mg/dL (265.2 µmol/L) (baseline, 1.5 mg/dL [132.6 µmol/L]) |
Urine sodium | 40 mEq/L (40 mmol/L) |
Fractional excretion of sodium | 2.1% |
Urinalysis | Specific gravity 1.012; pH 5.5; trace blood; trace protein; 1-3 normal-appearing erythrocytes/hpf; granular casts; tubular epithelial cells |
Kidney ultrasound is normal.
Which of the following is the most likely cause of this patient's acute kidney injury?