Review Question - QID 108865

A 67-year-old farmer presents to the emergency department with a chief complaint of confusion and flushing. His wife states that since this morning he has experienced dryness and flushing of his skin while working outside. As the day went on, the patient found it exceedingly difficult to urinate and had to create significant abdominal pressure for a weak stream of urine to be produced. Currently, the patient seems confused and responds incoherently. The patient has a past medical history of Parkinson disease, alcohol abuse, irritable bowel syndrome, anxiety, diabetes mellitus, hypertension, constipation, and a suicide attempt when he was 23 years old. He is currently taking lisinopril, hydrochlorothiazide, metformin, insulin, benztropine, levodopa/carbidopa, and vitamin C. The only other notable symptoms this patient has experienced are recent severe seasonal allergies. His temperature is 99.5°F (37.5°C), pulse is 112/min, blood pressure is 130/90 mmHg, respirations are 18/min, and oxygen saturation is 96% on room air. A physical exam shows dry, flushed skin in a confused male. Which of the following is the most likely cause of this patient's presentation?