Starting Dose of Memantine
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 reduction to 5 mg twice daily in patients with severe renal impairment (creatinine clearance 5-29 mL/min). 11
Standard Dosing Regimen
The FDA-approved titration schedule is straightforward and should be followed systematically 11:
- 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) - this is the therapeutic target dose
Key administration points:
- Minimum interval between dose increases is one week
- Can be taken with or without food
- If doses are missed for several days, resume at lower doses and retitrate
Renal Impairment Adjustments
Severe renal impairment (CrCl 5-29 mL/min): Target dose is 5 mg twice daily (total 10 mg/day) 11. This recommendation is supported by pharmacokinetic data showing that severe renal impairment increases memantine exposure by 115%, with predicted steady-state concentrations at 5 mg twice daily being comparable to those in patients with normal renal function receiving 10 mg twice daily 2.
Mild to moderate renal impairment (CrCl 30-80 mL/min): No dose adjustment is required 11. Pharmacokinetic studies demonstrate that while exposure increases by 60% in moderate impairment, this does not necessitate dose modification for the standard 10 mg twice daily regimen 2. Japanese population studies confirmed similar findings, showing 1.62-fold and 1.97-fold increases in exposure for mild and moderate impairment respectively 3.
Important Clinical Considerations
Hepatic impairment: Use with caution in severe hepatic impairment, though no specific dose adjustment is provided in the labeling 11.
Genitourinary conditions: Be aware that conditions raising urine pH (e.g., renal tubular acidosis, severe urinary tract infections) can decrease urinary elimination and increase plasma memantine levels 1.
Common pitfall: The slow weekly titration is essential for tolerability. Rushing the titration increases the risk of adverse effects including dizziness, headache, confusion, and constipation 1. Studies comparing once-daily versus twice-daily dosing at the target dose showed similar tolerability profiles 4, but the gradual titration remains standard practice.
Polypharmacy consideration: In patients already on extensive medication regimens (>10 medications), be particularly vigilant about tolerability, as polypharmacy significantly predicts adverse effects when memantine is added to existing therapy 5.