Memantine

Antidementia Drug

Drug class: NMDA Receptor Antagonist

Memantine (EBIXA) (中文：美金剛)

Common Strengths of Memantine

• 10 mg, 20 mg

Drug Trade Names

• Ebixa

Drug Usage

Memantine is primarily used in the treatment of moderate to severe Alzheimer's disease.

Mechanism of Action

Memantine blocks the NMDA receptors in the brain, which are activated by glutamate. This action helps prevent excessive neuronal excitability and protects against excitotoxicity, which can lead to neuronal death. Unlike complete antagonist, memantine allows for normal synaptic transmission at physiological levels of glutamate.

Route of Administration

• Oral tablet

Dosages

• Start at 5 mg once daily, increasing to a maximum of 10 mg twice daily.

Side Effects

Frequency	Adverse reactions
Common Side Effects	Dizziness
	Confusion
	Headache
	Constipation
	Diarrhea
Serious Side Effects	Hallucinations
	Severe allergic reactions (e.g. difficulty breathing)
	Shortness of breath

Pharmacokinetics

• Memantine undergoes minimal metabolism, primarily in the liver. It is not significantly affected by cytochrome P450 enzyme, which reduces the potential for drug interactions.
• Excretion: Approximately 57% to 82% of memantine is excreted unchanged in urine.
• Half-Life: The terminal elimination half-life ranges from 60 to 80 hours, allowing for once-daily dosing in clinical settings.
• Onset Time: Typically, within hours after administration.
• Duration: Effects can last up to 24 hours.

Drug Precautions

Pregnancy

The safety of memantine during pregnancy has not been firmly established.

Breastfeeding

The effects of memantine during breastfeeding are also unknown; thus, caution is advised.

Children and Elderly

• Children: Safety and efficacy have not been established in pediatric populations.
• Elderly: Dosage adjustments may be necessary due to increased sensitivity and potential renal impairment.

Drug Monitoring Items

Monitoring should include:

• Renal function (eGFR)
• Neurological status (cognition and behavior changes)
• Side effects such as dizziness, constipation, headache, and drowsiness. Serious adverse effects such as confusion or hallucinations should prompt immediate reevaluation of the treatment plan

Drug Interactions

Memantine can interact with several medications, leading to increased side effects or reduced effectiveness. Key interactions include:

• NMDA Antagonists: Co-administration with other NMDA antagonists such as amantadine and dextromethorphan (cough suppressant) should be approached with caution, as they may enhance the adverse reaction associated with memantine.
• Antacid: Certain antacids containing sodium bicarbonate can alter the excretion of memantine, potentially increasing its levels in the body.
• Warfarin: There is a caution regarding the concurrent use of warfarin, a blood thinner, due to potential alterations in its effectiveness when combined with memantine.

FAQ

How Should I Take the Tablet?

It can be taken with or without food.

What Should I Avoid While Taking?

Avoid alcohol and medications that can affect kidney function without consulting your healthcare provider. Additionally, avoid taking other NMDA antagonists concurrently.

What Happens if I Miss a Dose?

If you miss a dose, take it as soon as you remember unless it is almost time for your next dose. Do not double up on doses.