Memantine

In a healthy brain, glutamate is the main excitatory neurotransmitter — it helps nerve cells communicate and is essential for learning and memory ^{[1, 2]}. After glutamate sends its signal through NMDA receptors, it is quickly cleared away, and the receptors return to a resting state.

In Alzheimer's disease, this process goes wrong. Damaged nerve cells leak excess glutamate, which chronically overstimulates NMDA receptors ^[2]. This sustained overstimulation — called excitotoxicity — creates constant background 'noise' that both damages neurons and makes it harder for the brain to form new memories.

Memantine acts as a moderate-affinity, uncompetitive NMDA receptor antagonist ^{[1, 2]}. It sits in the NMDA receptor channel and blocks the constant low-level background stimulation caused by excess glutamate. However, when a strong, meaningful signal arrives (such as during learning), the surge of glutamate is powerful enough to push memantine out of the channel, allowing the signal through.

This selective action means memantine reduces harmful background noise while still permitting normal signal transmission — helping preserve cognitive function without completely blocking NMDA receptors.

Weeks 1-4 (dose titration): Memantine is started at a low dose and gradually increased over several weeks to minimize side effects ^[1]. During this titration period, it is too early to expect noticeable cognitive improvement. Some patients may experience mild dizziness, headache, or confusion during dose adjustment.

Months 1-3: After reaching the maintenance dose, benefits may begin to emerge over the first 1-3 months ^{[1, 2]}. The effects are often subtle — caregivers may notice that the patient maintains daily activities better, has somewhat improved attention, or shows less agitation compared to what might be expected with disease progression.

Long-term: Memantine does not halt Alzheimer's progression, but clinical trials showed that patients on memantine maintained better cognitive function and daily living skills compared to those on placebo over 6-12 months ^{[1, 2]}. The combination of memantine plus donepezil has shown benefits greater than either drug alone in moderate-to-severe Alzheimer's disease ^[2].

Memantine has minimal food interactions ^[1].

Food: May be taken with or without food. Food does not affect the absorption of memantine ^[1]. The extended-release capsule (Namenda XR) can be opened and sprinkled on applesauce for patients who have difficulty swallowing — do not chew or crush the pellets.

Alcohol: Alcohol should be avoided or minimized in patients taking memantine. Both substances affect the central nervous system, and combining them may worsen confusion, dizziness, and drowsiness — symptoms already common in Alzheimer's disease.

Caffeine: No significant interaction. However, excessive caffeine may increase agitation in some Alzheimer's patients.

Memantine dosing requires gradual titration ^[1].

Immediate-release tablets (Namenda): - Week 1: 5 mg once daily ^[1] - Week 2: 5 mg twice daily (10 mg/day) ^[1] - Week 3: 10 mg in the morning, 5 mg in the evening (15 mg/day) ^[1] - Week 4 and beyond: 10 mg twice daily (20 mg/day) ^[1] - Minimum interval between dose increases: 1 week

Extended-release capsules (Namenda XR): - Week 1: 7 mg once daily ^[1] - Week 2: 14 mg once daily ^[1] - Week 3: 21 mg once daily ^[1] - Week 4 and beyond: 28 mg once daily ^[1]

Renal impairment (severe, CrCl 5-29 mL/min): - Immediate-release: 5 mg twice daily (10 mg/day maximum) ^[1] - Extended-release: 14 mg once daily maximum ^[1]

Switching from IR to XR: Patients on 10 mg IR twice daily can switch to 28 mg XR once daily the next day ^[1].

Administration: IR tablets can be taken with or without food. XR capsules should be swallowed whole or contents sprinkled on applesauce (do not chew or crush pellets).

Memantine is available as a generic medication, reducing costs substantially ^{[1, 3]}.

Typical pricing (approximate 2025 prices): - Brand-name Namenda: Not widely available at retail - Brand-name Namenda XR: $300-500/month - Generic memantine IR: $10-30/month - Generic memantine XR: $30-80/month

Savings strategies: - Generic substitution: Generic memantine has been available since 2015 (immediate-release) and offers dramatic cost savings ^[3]. - Pharmacy discount programs: GoodRx and similar programs can reduce generic memantine costs to under $15/month. - Medicare Part D: Most Medicare plans cover generic memantine with low copays. Check your formulary. - Combination product: Generic memantine XR/donepezil (Namzaric) may simplify treatment and reduce costs if both medications are prescribed.

Pregnancy: Memantine is not typically relevant to pregnancy because Alzheimer's disease primarily affects older adults ^[1]. There are no adequate and well-controlled studies in pregnant women. Animal studies at high doses showed decreased body weight in offspring. Use during pregnancy only if clearly needed.

Breastfeeding: It is not known whether memantine is excreted in human breast milk ^[1]. Memantine is unlikely to be prescribed to women of reproductive age given its indication for Alzheimer's disease.

Generic memantine has been available in the United States since 2015 (immediate-release) ^[3].

Brand names: - Namenda (immediate-release): 5 mg and 10 mg tablets; also available as oral solution (2 mg/mL). Manufactured by Allergan/AbbVie. - Namenda XR (extended-release): 7 mg, 14 mg, 21 mg, and 28 mg capsules - Namzaric (memantine XR + donepezil): combination capsules for patients taking both medications

Generic memantine: - Multiple manufacturers produce FDA-approved generics in all formulations - Rated therapeutically equivalent (AB-rated) by the FDA - The vast majority of prescriptions are filled with generic

Related medication: Donepezil (Aricept) is a cholinesterase inhibitor commonly used in combination with memantine. The combination of memantine + donepezil has shown greater benefit than either drug alone for moderate-to-severe Alzheimer's disease ^[2].