What is the equivalent immediate-release dose for a 28 mg delayed-release memantine capsule?

Memantine 28 mg DR Capsule Equivalent in Immediate Release Form

The equivalent immediate-release dose for a 28 mg delayed-release memantine capsule is 20 mg per day, administered as 10 mg twice daily.

Dosing Conversion

The 28 mg extended-release (ER) formulation taken once daily is not directly equivalent to the immediate-release (IR) formulation on a milligram-per-milligram basis. According to FDA labeling, the standard therapeutic dose for memantine IR is 20 mg/day given as 10 mg twice daily 1. The 28 mg ER formulation was specifically designed to provide comparable therapeutic efficacy to the 20 mg/day IR regimen, despite the higher total daily dose 2.

Key Pharmacokinetic Considerations

• The ER formulation provides greater drug exposure than the IR formulation due to its higher total daily dose and modified release characteristics 2
• Despite this difference in exposure, both formulations are considered therapeutically equivalent for moderate to severe Alzheimer's disease
• The clinical implications of the higher exposure with ER formulation remain unclear, as no head-to-head comparative trials have been conducted 2

Practical Conversion Algorithm

When switching from memantine 28 mg ER to IR:

1. Discontinue the 28 mg ER capsule
2. Initiate memantine IR at 20 mg/day (10 mg twice daily)
3. No titration is necessary if the patient has been stable on the ER formulation
4. Monitor for symptom changes during the first 1-2 weeks after conversion

Important Caveat for Renal Impairment

If the patient has severe renal impairment (creatinine clearance 5-29 mL/min), the target IR dose should be reduced to 5 mg twice daily (10 mg total daily) 1.

Clinical Context

Both formulations demonstrate efficacy in moderate to severe Alzheimer's disease, with strong evidence supporting their use for improving cognition and global function 3. The primary advantage of the ER formulation is convenience and potentially improved adherence due to once-daily dosing 2, but when converting to IR, the standard 20 mg/day divided dose remains the appropriate therapeutic equivalent.