A 56-year-old man is brought to the emergency department by his wife because of memory loss and difficulty walking. She has noticed personality changes, truancy from work, and lack of personal care over the past 1 year. On examination he appears unkempt, smells of urine, and is uncooperative. He cannot recall the date or season, and gets angry when asked questions. His answers are often fabricated when checked with his wife. The blood pressure is 150/90 mm Hg, pulse 100/min, and he is diaphoretic and tremulous. His gait is wide based, and motor strength and reflexes are normal. His ocular movements are normal but there is nystagmus on lateral gaze. In the past he has had multiple admissions for alcohol withdrawal. Which of the following is the most appropriate next step in management?