This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.N.S, Subject name: Pharmacology
NMDA antagonist used in Alzheimer's disease is: 
Select and explain. 
A. Memantine, B. Rivastigmine, C. Donepezil, D. Galantamine
A: Memantine
Answer: A: Memantine 
Explanation: Ans: A (Memantine) Ref: Goodman and Gilman's "Phannacologica! Basis of Therapeutics'' 12th eci p.622Explanation:Memantine* It is used either as an adjunct or an alternative to cholinesterase inhibitors in Alzheimer's disease, and is also commonly used to treat other neurodegenerative dementias,Memantine is a noncompetitive antagonist of the NMDA-type glutamate receptor.It interacts with the Mg2+ binding site of the channel to prevent excessive activation while sparing normal function.Adverse effects of memantine include headache or dizziness, hut are usually mild and reversible.The drug is excreted by the kidneys and dosage should be reduced in patients with severe renal impairment.