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
All are cholinergic agents except I 
Select and explain. 
A. Galantamine, B. Donepezil, C. Tacrine, D. Memantine
D: Memantine
Answer: D: Memantine 
Explanation: Refer kDT 6/e p 472,473 Donepazil, rivastigmine, gallantamine and tacrine are cholinergic drugs( due to inhibition of cholenesterase enzyme)useful for Alzheimer's disease Memantine is an NMDA blocker, used for Alzheimer's disease