Memantine — Namenda — is the NMDA glutamate receptor antagonist for moderate-to-severe Alzheimer's. The mechanism is fundamentally different from AChEIs: rather than amplifying cholinergic signaling, memantine attenuates excessive glutamatergic signaling that contributes to ongoing neuronal injury in advanced disease.
- Class
- NMDA glutamate receptor antagonist (low-affinity, voltage-dependent)
- Mechanism
- Uncompetitive NMDA receptor antagonist — blocks pathological glutamate signaling while preserving normal signaling (voltage-dependent affinity). Reduces excitotoxic neuronal injury.
- Typical dose
- 5 mg daily, titrate over 4 weeks to 10 mg BID; ER 28 mg daily
- Half-life
- ~60-80 hours
- FDA indications
- Moderate to severe Alzheimer's disease
- Key adverse effects
- Dizziness, headache, confusion, constipation, somnolence
Different mechanism from AChEIs — often combined (memantine + donepezil) in moderate-severe disease. Generally well-tolerated. Combination product Namzaric (memantine + donepezil) available.
The voltage-dependence is what makes memantine usable. Standard NMDA antagonists (ketamine, dextromethorphan) block NMDA broadly and produce dissociation, confusion, and addiction risk. Memantine is a low-affinity, voltage-dependent antagonist — it blocks pathological NMDA signaling (excessive, prolonged glutamate exposure of the kind seen in Alzheimer's excitotoxicity) while preserving normal physiological NMDA signaling (the brief, regulated signals needed for normal learning and memory). The selectivity is what lets memantine work without producing the dissociative or cognitive side effects of broader NMDA blockers.
Memantine treats Alzheimer's through a different mechanism than the cholinesterase inhibitors — it dampens pathological glutamate signaling without blocking normal transmission.
Mechanism note: Memantine dampens excitotoxic glutamate 'noise' while sparing normal NMDA signaling — a well-tolerated, non-cholinergic agent for moderate-severe disease, frequently combined with a cholinesterase inhibitor.
FDA approval is for moderate-to-severe Alzheimer's. Trial data support modest cognitive and functional benefit. The effect is incremental — like AChEIs, memantine slows decline rather than reversing it.
Memantine is often combined with an AChEI in moderate-to-severe disease. The mechanisms are complementary — cholinergic enhancement plus glutamate excitotoxicity protection. The combination product Namzaric (donepezil + memantine) simplifies adherence. Combination produces modest additional benefit over either monotherapy.
Side effects are generally favorable — much less GI burden than AChEIs. Headache, dizziness, confusion, constipation, somnolence occur. The drug is renally cleared; dose-adjust in CKD.
Dosing: titrate over 4 weeks from 5 milligrams daily to 10 milligrams BID; or use the extended-release 28 milligrams daily formulation. Slow titration reduces side effects.
- Cost
- Generic ~$10-30/month. Namzaric (donepezil + memantine combination) ~$300+/month.
- Generic status
- Memantine generic since 2015. Namzaric brand-only.
- Formulary typical
- Memantine: Tier 1 generic. Namzaric: PA usually requires demonstrated adherence to component therapy.
- Access friction
- Memantine alone is easy. Namzaric (the combination product) faces PA.
Prescriber tip: For most patients, separate generic donepezil + generic memantine is cheaper than Namzaric. Reserve Namzaric for patients where adherence to once-daily combination is the differentiator.
For moderate-to-severe Alzheimer's, memantine added to an AChEI is the standard. For mild disease, memantine is not FDA-indicated, though it is sometimes used off-label.