Memantine is primarily used in Alzheimer's disease to modulate the effects of glutamate and alter calcium influx into neurons. Which statement best describes this mechanism?

• A. Memantine modulates the effects of glutamate to alter calcium influx into neurons.
• B. Memantine increases acetylcholine release to enhance signaling.
• C. Memantine blocks dopamine receptors to reduce motor symptoms.
• D. Memantine inhibits GABA synthesis to reduce inhibition of neural activity.

Answer: (A)

Memantine works by blocking excessive activity at NMDA receptors, which are activated by glutamate and drive calcium entry into neurons. In Alzheimer's disease, too much glutamate can cause overactivation, leading to calcium influx that contributes to excitotoxicity and cell damage. Memantine is an NMDA receptor antagonist that binds in a use- and voltage-dependent way, preferentially blocking the channel when glutamate levels are high and neurons are depolarized, while allowing normal synaptic transmission to continue. By dampening this excessive calcium influx, memantine modulates glutamatergic signaling and protects neurons from excitotoxic injury.

This is why the statement describing memantine as modulating the effects of glutamate to alter calcium influx is the best fit. It’s not about increasing acetylcholine release (that would relate to cholinesterase inhibitors like donepezil), nor about blocking dopamine receptors or inhibiting GABA synthesis, which are the mechanisms of other drug classes and not memantine’s action.