This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
[{'content': 'Therapeutic drug monitoring is done for all the following except: \nSelect and explain. \nA. Phenytoin, B. Metformin, C. Tacrolimus, D. Cyclosporin', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]