A 34-year-old male with a known history of schizophrenia is brought to the psychiatric emergency department by police after threatening bystanders at a bus stop. He is pacing rapidly, shouting about government surveillance, and has overturned a chair in the triage area. He refuses to sit or engage in conversation. His vital signs show heart rate 112, blood pressure 158/94, temperature 37.1 C, and respiratory rate 22. He has no known allergies and his home medication list includes oral risperidone 4 mg daily, which he reports he stopped taking three weeks ago. The PMHNP is planning acute management. Which of the following represents the most appropriate initial treatment approach?