A 54-year-old woman is hospitalized for management of acute kidney injury. Medical history is significant for obesity but is otherwise unremarkable. She reports that she was seen in a weight loss clinic 1 month ago and was prescribed an unknown weight reduction drug, which she has been taking since that time. She takes no other medications.
On physical examination, blood pressure is 140/70 mm Hg, and pulse rate is 72/min. BMI is 40. Estimated central venous pressure is 10 cm H2O. There are crackles at the lung bases. Heart examination is unremarkable. There is lower extremity edema to the mid-calf bilaterally. The remainder of the examination is unremarkable.
Laboratory studies show a serum creatinine level of 5.1 mg/dL (450.8 µmol/L). Urinalysis is dipstick positive for trace protein, and urine sediment is notable for 0-2 erythrocytes/hpf, 0-5 leukocytes/hpf, and numerous calcium oxalate crystals.
Kidney ultrasound demonstrates normal-sized kidneys with slightly increased echogenicity and no hydronephrosis. Kidney biopsy demonstrates deposition of calcium oxalate crystals within the tubules and the interstitium.
Which of the following is the most likely cause of this patient's acute kidney injury?