Memantine Starting Dose: 5 mg Once Daily
The recommended starting dose of memantine for adults with Alzheimer's disease is 5 mg once daily, not 2.5 mg. The FDA-approved dosing regimen clearly specifies this initial dose, which is then titrated upward in 5 mg increments over subsequent weeks 1.
Standard Dosing Protocol
The FDA label provides explicit guidance on memantine initiation and titration 1:
- Week 1: Start at 5 mg once daily
- Week 2: Increase to 10 mg/day (5 mg twice daily)
- Week 3: Increase to 15 mg/day (5 mg and 10 mg as separate doses)
- Week 4+: Target dose of 20 mg/day (10 mg twice daily)
The minimum interval between dose increases is one week, allowing assessment of tolerability before advancing to the next dose level 1.
Why Not 2.5 mg?
A starting dose of 2.5 mg is not part of the standard FDA-approved regimen for typical patients. The only scenario where 2.5 mg dosing appears is in the oral solution formulation measurements (2 mg/mL concentration, where 2.5 mL = 5 mg), but this is a volume measurement, not the actual starting dose 1.
Special Population Exception
The only indication for a lower maintenance dose is severe renal impairment (creatinine clearance 5-29 mL/min), where the target dose is reduced to 5 mg twice daily (10 mg/day total) 1. However, even in this population, the starting dose follows the standard titration beginning at 5 mg once daily.
Evidence for Efficacy
The 20 mg/day target dose has been consistently demonstrated as effective in controlled trials for moderate-to-severe Alzheimer's disease 2, 3:
- Cognitive function: Improvement of 3.11 points on the Severe Impairment Battery
- Activities of daily living: Benefit of 1.09 points on ADL19
- Global clinical impression: 0.21 points improvement on CIBIC+
- Behavioral symptoms: 1.84 points improvement on NPI
These benefits are seen both as monotherapy and in combination with cholinesterase inhibitors 2, 4.
Clinical Considerations
Memantine can be taken with or without food, which may help with tolerability 1. The most common adverse effects (≥5%) include dizziness, headache, confusion, and constipation, though overall discontinuation rates are comparable to placebo 1, 3.
Important caveat: For patients with mild Alzheimer's disease (MMSE 20-23), evidence suggests memantine probably provides no benefit and may increase discontinuation rates due to adverse events 3. The drug is FDA-approved and evidence-supported specifically for moderate-to-severe dementia.
If a patient misses several days of treatment, dosing should be resumed at lower doses and retitrated according to the standard schedule 1.