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 drugs except 
Select and explain. 
A. Memantine, B. Tacrine, C. Rivastigmine, D. Donepezil
A: Memantine
Answer: A: Memantine 
Explanation: Memantine acts on NMDA receptors .remaining all the drugs are indirectly acting cholinergicn drugs used in the treatment of alzhimers disease. Ref: KDT 6th ed pg 472,473