Memantine Hydrochloride Bristol Laboratories (Memantine Hydrochloride)

• Memantine is an NMDA receptor antagonist used in the management of Alzheimer’s disease.
• Alzheimer’s disease: improves cognition and functional abilities in patients with moderate to severe disease.

• Memantine binds to the phencyclidine site of the N‑methyl‑D‑aspartate (NMDA) receptor as a non‑competitive antagonist. By blocking excessive calcium influx caused by overstimulation of glutamate, it reduces excitotoxic neuronal injury while preserving normal synaptic transmission. This modulation of glutamatergic activity helps maintain neuronal viability and supports cognitive function in Alzheimer’s disease. The drug’s low affinity and rapid off‑rate allow physiological neurotransmission to continue, minimizing adverse effects associated with complete NMDA blockade.

Memantine may be associated with a range of adverse reactions, which are categorized by frequency.

Common Side Effects

• Dizziness: sensation of light‑headedness or unsteadiness.
• Headache: mild to moderate pain in the head region.
• Constipation: reduced bowel movements or hard stools.
• Confusion: transient disorientation or difficulty concentrating.
• Fatigue: feeling unusually tired or weak.
• Hypertension: elevated blood pressure readings.

Serious or Rare Side Effects

• Seizures: uncontrolled electrical activity in the brain.
• Hallucinations: seeing or hearing things that are not present.
• Cardiac arrhythmia: irregular heart rhythm that may require monitoring.
• Severe allergic reaction: rash, swelling, or difficulty breathing.
• Stevens‑Johnson syndrome: rare skin disorder with blistering.
• Suicidal thoughts: emergence of self‑harm ideation.

When prescribing memantine, clinicians should consider several safety factors.

• Renal impairment: adjust dose or monitor renal function.
• Hepatic impairment: use with caution in patients with liver disease.
• History of seizures: assess risk and monitor neurological status.
• Elderly patients: start at low dose and titrate slowly.
• Concomitant NMDA antagonists: avoid combined use to prevent excess blockade.
• Store at ambient temperature: keep in the original container, protect from moisture.

Memantine can interact with other medicines, requiring attention to avoid reduced efficacy or increased toxicity.

Major Interactions (Avoid)

• Amantadine: additive NMDA antagonism may increase neurotoxicity.
• Dextromethorphan: combined use can cause severe CNS depression.
• Ketamine: heightened risk of psychomimetic effects.

Moderate Interactions (Monitor Closely)

• Donepezil: may require dose adjustment for optimal cognitive benefit.
• Antihypertensives: monitor blood pressure for additive hypotensive effect.
• Antipsychotics: observe for increased sedation or extrapyramidal symptoms.