This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Drugs, Subject name: Medicine
[{'content': 'Which of the following opioid analgesics is most likely to cause central nervous system (CNS) disturbance? \nSelect and explain. \nA. heroin, B. morphine, C. meperidine, D. fentanyl', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Meperidine has a half-life of 3 hours, but it has an active metabolite, normeperidine, which has a half-life of 15-20 hours. Therefore, accumulation of normeperidine with toxicity is common. The drug should not be used for prolonged periods (over 48 hours), and probably should not be used at all in those susceptible to delirium (e.g., the elderly).', 'role': 'assistant'}]