Correct (2): Memantine is an NMDA receptor antagonist that reduces glutamate excitotoxicity. It is used in moderate-to-severe Alzheimer disease, often combined with a cholinesterase inhibitor (donepezil, rivastigmine, galantamine) for additional symptomatic cognitive benefit — the two mechanisms are complementary, not redundant. (1) Not a replacement. (3) Different mechanism. (4) Alzheimer is not reversed; both classes slow decline modestly.
For study reference only. Always follow current clinical guidelines and your institution’s protocols.