Memantine Dosing for Moderate-to-Severe Alzheimer's Disease
Start memantine at 5 mg once daily and titrate by 5 mg increments weekly to a target maintenance dose of 20 mg/day (10 mg twice daily), with dose reduction to 5 mg twice daily in patients with severe renal impairment (creatinine clearance 5-29 mL/min). 1
Standard Titration Schedule
The FDA-approved titration follows a structured 4-week escalation 1:
- Week 1: 5 mg once daily
- Week 2: 10 mg/day (5 mg twice daily)
- Week 3: 15 mg/day (5 mg and 10 mg as separate doses)
- Week 4 onward: 20 mg/day (10 mg twice daily) - target maintenance dose
Minimum interval between dose increases is one week. This gradual titration minimizes adverse effects while achieving therapeutic levels 1.
Key Administration Details
- Can be taken with or without food 1
- If a single dose is missed: Do not double the next dose; resume regular schedule 1
- If multiple doses are missed: Resume at lower dose and retitrate upward 1
Renal Impairment Adjustments
Memantine is primarily renally eliminated, requiring dose modification based on creatinine clearance 1, 2:
- Normal renal function (CrCl >80 mL/min): Standard 20 mg/day (10 mg twice daily)
- Mild impairment (CrCl 50-80 mL/min): No adjustment needed - standard 20 mg/day 2
- Moderate impairment (CrCl 30-49 mL/min): No adjustment needed - standard 20 mg/day 2
- Severe impairment (CrCl 5-29 mL/min): Reduce target to 10 mg/day (5 mg twice daily) 1, 2
The pharmacokinetic data shows that severe renal impairment increases drug exposure by 115%, necessitating the dose reduction to maintain safe plasma levels 2.
Hepatic Impairment
Administer with caution in severe hepatic impairment, though no specific dose adjustment is mandated 1. Monitor closely for adverse effects.
Clinical Context for Efficacy
Memantine at 20 mg/day demonstrates small but consistent clinical benefits in moderate-to-severe AD across multiple domains 3, 4:
- Cognition (3.11 points on Severe Impairment Battery)
- Activities of daily living (1.09 points on ADL19)
- Global clinical impression (0.21 points on CIBIC+)
- Behavior and mood (1.84 points on NPI)
Important caveat: Evidence for mild AD (MMSE 20-23) shows no benefit 4. Memantine is indicated specifically for moderate-to-severe dementia 1, 5.
Combination with Cholinesterase Inhibitors
Memantine can be safely combined with donepezil or other cholinesterase inhibitors without dose adjustment 6. The combination shows additive benefits in moderate-to-severe AD, with the same 20 mg/day target dose 6.
Safety Profile
Discontinuation rates due to adverse events are low (7.4% vs 12.4% for placebo) 6. Most common adverse effects include:
- Dizziness (6.1% vs 3.9% placebo) - 1.6-fold increased risk 4
- Headache (5.5% vs 4.3% placebo) 4
- Confusion (≥5%) 1
Critical warning: Conditions that raise urine pH (e.g., renal tubular acidosis, severe UTIs, alkaline diet) decrease urinary elimination and increase plasma levels - monitor closely 1.
Duration Considerations
The 2020 Canadian Consensus guidelines recommend considering discontinuation after >12 months if 7:
- Clinically meaningful worsening over 6 months
- No observed benefit during treatment
- Severe/end-stage dementia
- Intolerable side effects (confusion, dizziness, falls)
Deprescribing should be gradual: reduce dose by 50% every 4 weeks until reaching starting dose, then discontinue after 4 weeks 7.