Memantine (Namenda) Dosing
Start memantine at 5 mg once daily and titrate up by 5 mg increments weekly to a target dose of 20 mg/day (10 mg twice daily), with dose reductions to 5 mg twice daily (10 mg total daily) required for patients with severe renal impairment (creatinine clearance 5-29 mL/min). 1
Standard Dosing Regimen
The FDA-approved titration schedule for memantine immediate-release 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 morning, 10 mg evening)
- Week 4 onward: 20 mg/day (10 mg twice daily) - target maintenance dose
Key point: The minimum interval between dose increases is one week. Memantine can be taken with or without food 1.
Extended-Release Formulation
An extended-release formulation (Namenda XR) is available at 28 mg once daily, providing higher total daily exposure than the immediate-release 20 mg/day regimen 2. The ER capsules can be opened and sprinkled on applesauce for patients with swallowing difficulties 2. While pharmacokinetic data show greater drug exposure with the ER formulation, the clinical implications remain unclear as no head-to-head trials have compared the two formulations 2.
Renal Dose Adjustments
Critical consideration: Memantine is primarily renally eliminated, making dose adjustment essential in renal impairment 3.
Dosing by Renal Function:
- Normal function (CrCl >80 mL/min): Standard 20 mg/day (10 mg BID)
- Mild impairment (CrCl 50-80 mL/min): No adjustment needed - standard 20 mg/day 3
- Moderate impairment (CrCl 30-49 mL/min): No adjustment needed - standard 20 mg/day 3
- Severe impairment (CrCl 5-29 mL/min): Reduce to 10 mg/day (5 mg BID) 1, 3
Pharmacokinetic studies demonstrate that AUC increases by 60% in moderate renal impairment and 115% in severe renal impairment 3. However, simulations predict that the standard 10 mg BID dosing maintains safe steady-state concentrations in mild and moderate impairment, while severe impairment requires the reduced 5 mg BID regimen to avoid excessive drug accumulation 3.
Common Pitfall:
A retrospective study found that 60% of patients requiring renal dose adjustment were not prescribed the appropriate reduced dose 4. Always calculate creatinine clearance using the Cockcroft-Gault equation before initiating memantine 1:
- Males: CrCl = [140-age] × Weight(kg) / [72 × serum creatinine(mg/dL)]
- Females: CrCl = 0.85 × [140-age] × Weight(kg) / [72 × serum creatinine(mg/dL)]
Clinical Indications and Evidence
Memantine is FDA-approved and strongly recommended for moderate to severe Alzheimer's disease 1, 5. The drug demonstrated significant benefits in:
- Cognition: Measured by Severe Impairment Battery (SIB), with mean difference of 3.4 points favoring memantine over placebo at 28 weeks 1
- Function: Assessed by ADCS-ADL, showing less functional decline compared to placebo 1
- Global outcomes: Clinically meaningful improvements on CIBIC-Plus scales 1
Combination therapy: When added to stable donepezil therapy in moderate-to-severe AD, memantine provided additional significant benefits across all outcome measures (cognition, activities of daily living, global status, and behavior) 6, 5.
For other dementias, evidence quality varies 5:
- Lewy body dementia: Strong recommendation for memantine
- Vascular dementia: Conditional recommendation
- Parkinson's disease dementia: Conditional recommendation
Safety and Tolerability
Memantine is generally well-tolerated with a favorable safety profile 6, 5. Common adverse events include:
- Headache
- Diarrhea
- Dizziness
- Confusion (particularly in elderly)
Important: Once-daily and twice-daily dosing regimens show similar safety profiles 7. Treatment discontinuation rates due to adverse events are relatively low (7.4% in clinical trials) 6.
Deprescribing Considerations
Per Canadian consensus guidelines, consider discontinuing memantine after >12 months if 8:
- Clinically meaningful worsening over past 6 months
- No observed benefit during treatment
- Severe/end-stage dementia with limited life expectancy
- Intolerable side effects (confusion, dizziness, falls)
- Poor medication adherence
Deprescribing protocol: Reduce dose by 50% every 4 weeks until reaching the initial starting dose, then discontinue after 4 weeks at starting dose 8. Reinitiate if clinically meaningful worsening occurs after cessation 8.