What is Memantine?
Memantine is an N-methyl-D-aspartate (NMDA) receptor antagonist—specifically a moderate-affinity, uncompetitive, voltage-dependent antagonist with fast on/off kinetics—approved for treating moderate to severe Alzheimer's disease dementia. 1
Mechanism of Action
Memantine works by blocking excessive NMDA receptor activity in the brain, which helps modulate glutamatergic dysfunction that contributes to neuronal damage in Alzheimer's disease. Unlike cholinesterase inhibitors that target acetylcholine, memantine represents a fundamentally different therapeutic approach by preventing pathological overstimulation of glutamate receptors while allowing normal physiological signaling to continue 2, 3.
Approved Indications
- Moderate to severe dementia of the Alzheimer's type 1
- Also used for Alzheimer's disease (AD), Parkinson's disease dementia (PDD), Lewy body dementia (DLB), and vascular dementia (VD) per Canadian guidelines 4
- Not indicated for mild cognitive impairment or mild AD 4—evidence shows no benefit in mild AD 5
Dosing Regimen
Standard Titration Schedule 1:
- Week 1: 5 mg once daily
- Week 2: 5 mg twice daily (10 mg/day total)
- Week 3: 10 mg morning + 5 mg evening (15 mg/day total)
- Week 4 onward: 10 mg twice daily (20 mg/day total—target maintenance dose)
Minimum interval between dose increases: 1 week
Key Dosing Considerations:
- Can be taken with or without food 1
- Available as immediate-release (IR) tablets/oral solution (20 mg/day divided twice daily) and extended-release (ER) capsules (28 mg once daily) 6
- If doses are missed for several days, restart at lower dose and retitrate 1
Renal Impairment Adjustments 1:
- Severe renal impairment (CrCl 5-29 mL/min): Target dose is 5 mg twice daily (10 mg/day total)
- Moderate renal impairment: No specific adjustment required, but monitor closely
- Conditions that raise urine pH decrease urinary elimination and increase plasma levels 1
Hepatic Impairment 1:
- Use with caution in severe hepatic impairment
- No specific dose adjustment provided
Clinical Efficacy
Moderate to Severe AD:
High-certainty evidence demonstrates small but consistent clinical benefits 7, 5:
- Cognition: Improvement of 3.11 points on Severe Impairment Battery
- Global function: 0.21 points on CIBIC+ scale
- Activities of daily living: 1.09 points on ADL19 scale
- Behavioral symptoms: 1.84 points on Neuropsychiatric Inventory
These benefits occur whether memantine is used alone or combined with cholinesterase inhibitors 8, 5. The combination of memantine plus donepezil shows additive benefits in moderate to severe AD 8.
Mild AD:
Memantine should NOT be used in mild AD 4—moderate-certainty evidence shows probably no benefit on cognition, function, or behavior, with possible increased discontinuation due to adverse events 5.
Vascular Dementia:
Moderate-certainty evidence suggests probable small benefit for cognition and behavior, but no difference in global status or activities of daily living 5.
Common Adverse Effects
Most Common (≥5% and greater than placebo) 1:
- Dizziness (6.1% vs 3.9% placebo)
- Headache (5.5% vs 4.3% placebo)
- Confusion
- Constipation
Other Notable Effects 7, 1:
- Gastrointestinal symptoms
- Agitation was LESS frequent in memantine groups than placebo in most studies
- Overall adverse event rate similar to placebo (RR 1.03)
- Discontinuation rate due to adverse events: 7.4% (similar to placebo at 11.5%)
Memantine is generally well-tolerated with a favorable safety profile 7, 9, 5.
Important Clinical Considerations
When to Consider Discontinuation 4:
After >12 months of treatment, consider stopping if:
- Clinically meaningful worsening despite treatment over past 6 months
- No benefit ever observed (no improvement, stabilization, or decreased decline rate)
- Severe/end-stage dementia with dependence in most basic ADLs
- Intolerable side effects (confusion, dizziness, falls)
- Poor medication adherence
Discontinuation Protocol 4:
- Taper gradually: Reduce dose by 50% every 4 weeks until reaching initial starting dose
- After 4 weeks at starting dose, can discontinue completely
- Reinitiate if clinically meaningful worsening occurs after cessation
Critical Pitfalls to Avoid:
- Do not use in mild AD or MCI—no evidence of benefit and potential for harm 4, 5
- Do not use for non-approved dementias (frontotemporal dementia, other neurodegenerative conditions) 4
- Adjust dose in severe renal impairment—failure to do so increases risk of adverse effects 1, 9
- Monitor urine pH-altering conditions—can significantly increase memantine levels 1