A 25 year old man is brought to the emergency department because of an overdose. He is agitated and has needed physical restraints due to violent behavior. Her temperature is 39°C (102.2°F), pulse is 130/min and blood pressure is 180/90 mm Hg. Physical examination shows diaphoresis, agitation and confusion. The pupils are mydriatic with minimal reactivity to light. Tone is normal. There is no clonus but reflexes are brisk. Abdominal examination shows increased bowel sounds. Which of the following medications is the most likely cause of his presentation?