A 45-yeаr-оld mаn with а 20-year histоry оf heavy alcohol use (one pint of whiskey daily) presents 12 hours after his last drink with tremors, diaphoresis, anxiety, nausea, tachycardia, and hypertension. His CIWA score is 18, indicating moderate withdrawal. He is alert and oriented without hallucinations or seizures. Which pharmacologic therapy is most appropriate to initiate at this time?