Review Question - QID 214196

A 73-year-old man is brought to the emergency department by his daughter after he felt lightheaded during dinner at home. She says that he was standing up to get more food when he started complaining of dizziness. She had him sit back down and his symptoms appeared to resolve; however, she was concerned that he may have accidentally mixed up his medications so she decided to bring him in for further evaluation. His past medical history is significant for benign prostatic hyperplasia, diabetes, and depression. He takes tamsulosin, metformin, glipizide, and fluoxetine. Blood and urine tests are performed with the following results:

Blood urea nitrogen: 71 mg/dL
Serum creatinine: 2.7 mg/dL
Urine sodium: 16 mEq/L
Urine osmolality: 628 mOsm/kg

Which of the following etiologies most likely explains this patient's symptoms and findings?