A 52-year-old man is brought to the emergency department by his wife with a 2-week history of depressed mood, inability to get out of bed, and complete loss of appetite. He reports feeling worthless and guilty about past failures in his business. On examination, he is psychomotor retarded, speaks in monosyllables, and has poor eye contact. He admits to recurrent thoughts that 'everyone would be better off without me' and has a detailed plan to hang himself using a rope in his garage. His wife reports he has never had a manic or hypomanic episode. What is the most appropriate immediate management?