Memantine (Namenda) is a low-affinity, uncompetitive NMDA receptor antagonist. Approved for moderate-to-severe Alzheimer's.
Mechanism — Blocks pathologic NMDA activation (excitotoxic glutamate) while sparing physiologic transmission. Distinct from ketamine in affinity and binding kinetics.
Use case — Alzheimer's. Off-label: chronic migraine prevention, OCD adjunct. Typical 10-20 mg/day after titration.
Caveats — Doesn't reverse Alzheimer's — slows symptomatic progression modestly. Dizziness, headache, and confusion are common early. Renal dose adjustment required.