A 29-year-old man with schizophrenia is brought to the emergency department after threatening another patient. He is pacing, shouting and clenching his fists; his temperature, pulse and blood pressure are normal, and there is no history of alcohol or stimulant use. He refuses to sit down or take oral medication and says, ‘If anyone comes near me, I will hit them.’ Staff have moved other patients away and called for assistance. Which one of the following is the most appropriate immediate management?