This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Autonomic nervous system, Subject name: Pharmacology
Which drug is not used now in Alzheimer's disease 
Select and explain. 
A. Tacrine, B. Galantamine, C. Donepezil, D. Rivastigmine
A: Tacrine
Answer: A: Tacrine 
Explanation: Because of hepatotoxicity,and requirements of frequent dosing,tacrine is less often used than other agents Ref-KDT 6/e p104,472,473