Memantine

Memantine is prescribed to treat:

• Moderate to severe alzheimer's disease • Various related conditions in the neurological category • Associated symptoms and complications

It is an important medication that helps manage these conditions effectively.

Memantine (Namenda) is an NMDA receptor antagonist used for moderate to severe Alzheimer's disease and other dementias. It works through a mechanism entirely different from the cholinesterase inhibitors, which is why the two are frequently used together rather than as alternatives.

Mechanism of Action

Glutamate is the principal excitatory neurotransmitter in the brain, and NMDA receptors mediate much of its action in learning and memory. In Alzheimer's disease, chronic excessive glutamate activity is thought to contribute to neuronal injury through excitotoxicity — sustained calcium influx that damages and eventually kills neurons.

Memantine is a low-affinity, uncompetitive, voltage-dependent NMDA receptor antagonist, and each of those qualifiers matters. It blocks the receptor channel, but binds loosely enough and leaves quickly enough that it does not prevent the brief, high-intensity glutamate signalling that normal learning requires. It preferentially blocks the sustained low-level activation that characterises excitotoxicity.

That selectivity is why memantine is tolerable where earlier, higher-affinity NMDA antagonists were not — those produced hallucinations and cognitive impairment by blocking normal signalling along with the pathological.

As with the cholinesterase inhibitors, the effect is symptomatic. Memantine does not clear amyloid, does not affect tau pathology, and does not halt neurodegeneration. Whether the excitotoxicity it addresses is a genuine driver of progression or a downstream consequence remains unsettled.

The magnitude of benefit is modest — small improvements in cognition, function, and behaviour, most evident in moderate to severe disease.

Clinical Use

Memantine is approved for moderate to severe Alzheimer's disease and, unlike donepezil, it is not indicated in mild disease, where trials have not shown benefit.

Combination with a cholinesterase inhibitor is common and rational, since the mechanisms are independent, and the combination is generally well tolerated. Whether it produces meaningfully more benefit than either alone is debated, but the tolerability is good enough that it is frequently tried.

Its tolerability profile is its practical advantage. Memantine does not cause the nausea, diarrhoea, anorexia, weight loss, and bradycardia that limit cholinesterase inhibitors, which matters in a frail population already at nutritional risk. Dizziness, headache, confusion, and constipation are the usual complaints, generally mild.

Titration is gradual over several weeks to limit dizziness and confusion, and an extended-release once-daily form exists alongside the twice-daily immediate-release.

Expectation setting matters as much here as with any dementia treatment. Families should understand that memantine may modestly slow decline and may help with agitation and daily function, but that memory will not improve and the disease will progress. Framed accurately, families can judge whether continuing is worthwhile. The dementia warning signs article covers early recognition, and our neurologic team manages diagnosis and treatment.

Monitoring and Follow-Up

No routine laboratory monitoring is required beyond kidney function, which matters because memantine is largely eliminated unchanged by the kidneys and requires dose reduction in significant impairment. Accumulation causes confusion and dizziness that is easily attributed to the dementia itself.

Cognitive and functional assessment at intervals guides whether to continue. Caregiver burden should be assessed as a matter of routine, since it predicts institutionalisation more strongly than the patient's cognitive score.

Urinary pH affects elimination — memantine clearance falls markedly in alkaline urine, which can occur with certain diets, urinary alkalinising agents, or renal tubular acidosis, raising levels. This is an unusual interaction worth knowing about when a stable patient becomes newly confused.

Deprescribing deserves the same attention as starting. In advanced dementia, once goals of care have shifted to comfort, continuing a drug with modest symptomatic benefit is often not in the patient's interest, and stopping should be a discussed decision rather than something that never arises. The MedlinePlus memantine entry covers prescribing detail, and the Alzheimer's Association treatment resource sets out what is available.

The Wider Picture

Medication is a small part of dementia care and it is worth being explicit about that rather than allowing a prescription to stand in for a plan.

Managing vascular risk factors, treating hearing loss, maintaining physical activity and social engagement, addressing sleep and mood, and reviewing the medication list for anticholinergic burden all matter at least as much. Anticholinergic drugs — bladder antimuscarinics such as oxybutynin, first-generation antihistamines, tricyclics — worsen cognition directly and are common in this population.

Behavioural and psychological symptoms are frequently the hardest part for families, and non-pharmacologic approaches should be exhausted before antipsychotics, which carry a boxed warning of increased mortality in dementia. Memantine itself may help modestly with agitation.

Planning — advance directives, driving, home safety, financial arrangements, caregiver support — has more impact on how the illness unfolds than any current drug does.

Special Populations

In older adults, which is essentially the entire treated population, kidney function should guide dosing and declines with age even when creatinine appears normal.

In significant kidney impairment, dose reduction is required. Hepatic impairment matters less. Memantine warrants caution in seizure disorders. It is not used in pregnancy, an essentially theoretical consideration given the indication.

Memantine is not indicated in mild cognitive impairment or mild Alzheimer's disease, and prescribing it there exposes patients to side effects without demonstrated benefit.

When to Contact Your Doctor

Report increased confusion, dizziness, unsteadiness, or falls, particularly after a dose change or if kidney function has altered — these may indicate accumulation rather than disease progression.

Report new or worsening agitation, hallucinations, or aggression. Report constipation, headache, or drowsiness that interferes with daily life. Report seizures.

If it is unclear whether the medication is helping, say so — that is a reasonable and answerable question, and a supervised trial off the drug is a legitimate way to find out.

To review whether memantine is providing benefit, discuss combination treatment, or plan care as the illness progresses, contact us or schedule a visit.