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: 
Select and explain. 
A. Gallantamine, B. Donepezil, C. Tacrine, D. Memantine
D: Memantine
Answer: D: Memantine 
Explanation: Ref: KD Tripathi pharmacology 7th edition (page.no:489) All these drugs are used in Alzheimer's disease. But only A,B,C increase cholinergic activity in Alzheimer's. Memantine is a Glutamate Antagonist.it is an NMDA blocker Examples of direct-acting cholinergic agents include choline esters (acetylcholine, methacholine, carbachol, bethanechol, tacrine) and alkaloids (muscarine, pilocarpine, cevimeline)