Memantin

Memantin is a medication used in the management of moderate to severe Alzheimer's disease. It is approved in many countries for this indication and may be prescribed alone or in combination with acetylcholinesterase inhibitors to improve patient functioning and reduce symptoms.

Mechanism of action is as a low- to moderate-affinity, uncompetitive antagonist of the N-methyl-D-aspartate (NMDA) receptor. By binding to the receptor’s open channel, memantine reduces excessive calcium influx and protects neurons from glutamate-induced excitotoxicity while allowing normal synaptic activity to continue at therapeutic levels. This mechanism is intended to provide symptomatic benefits with a relatively favorable side-effect profile.

Pharmacokinetics and administration: Memantine is well absorbed when taken by mouth and reaches peak plasma concentrations within 3 to 7 hours. It has a long elimination half-life, typically around 60 to 80 hours, and is excreted largely unchanged in the urine. Dose adjustments are recommended for renal impairment; hepatic metabolism plays a limited role in its clearance.

Dosing typically starts at 5 mg once daily for one week, then 5 mg twice daily for another week, followed by 10 mg twice daily (20 mg per day) as maintenance therapy. The dosage may be adjusted based on tolerability and renal function.

Common adverse effects include dizziness, headache, constipation, confusion, and fatigue. Other effects can include hypertension and rare neuropsychiatric symptoms. Memantine is generally well tolerated, and its use is often complementary to cholinesterase inhibitors in moderate to severe disease. Brand names include Namenda and Ebixa; generic memantine is also available.