This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Pharmacodynamics, Subject name: Pharmacology
[{'content': 'Which of the following drugs require therapeutic drug monitoring? \nSelect and explain. \nA. Metformin, B. Propranolol, C. Warfarin, D. Phenytoin', 'role': 'user'}, {'content': 'Answer: D \nExplanation: * Therapeutic drug monitoring is adjustment of dose of the drug according to its plasma concentration. It is required for A Aminoglycosides (e.g. gentamicin) Drug Digitalis Possessing Phenytoin (anti-epileptics) Low Lithium Therapeutic Tricyclic antidepressants Index Immunomodulators (e.g. cyclosporine)', 'role': 'assistant'}]