Memantine’s mechanism in Alzheimer's therapy is what?

• A. NMDA receptor antagonist
• B. Acetylcholinesterase inhibitor
• C. Dopamine receptor antagonist
• D. GABA receptor agonist

Answer: (A)

Memantine works by blocking NMDA receptors, which are activated by glutamate and can drive excitotoxic damage in Alzheimer's disease. It acts as an uncompetitive, use-dependent blocker of the NMDA receptor channel, meaning it preferentially blocks the receptor when the channel is open during excessive glutamate activity. This reduces calcium influx and neuronal stress without shutting down normal, physiological signaling needed for learning and memory. Its moderate affinity and voltage dependence allow it to dampen pathological NMDA activity while preserving everyday synaptic transmission, which is why it can offer cognitive and functional benefits in moderate to severe stages when excitotoxic processes are more prominent. It is often used in combination with acetylcholinesterase inhibitors, which work by increasing acetylcholine levels to support cholinergic transmission. Memantine, however, does not inhibit acetylcholinesterase, nor does it primarily affect dopamine or GABA receptors, so those mechanisms are not relevant to its action in treating Alzheimer's disease.