Memantine (Namenda)
Memantine Indications
| Indication | Approved Population | Therapy Type | Status |
|---|---|---|---|
| Moderate-to-severe dementia of the Alzheimer’s type | Adults | Monotherapy or adjunctive with AChE inhibitor | FDA Approved |
Memantine is the only FDA-approved drug for Alzheimer’s disease that works outside the cholinergic system. Unlike acetylcholinesterase inhibitors (donepezil, rivastigmine, galantamine), which target mild-to-moderate disease, memantine is indicated for the moderate-to-severe stage. It is frequently prescribed in combination with a cholinesterase inhibitor, most commonly donepezil, and the fixed-dose combination product Namzaric (memantine XR + donepezil) is available for this purpose. In pivotal trials, memantine demonstrated significant improvements on both cognitive (SIB) and functional (ADCS-ADL) measures relative to placebo.
Vascular dementia: The Latvian Study 3 included patients with vascular dementia and showed functional benefit. Some international guidelines support use in vascular dementia. Evidence quality: Moderate.
Dementia with Lewy bodies (DLB): Limited RCT data; some clinical benefit reported in open-label studies. Evidence quality: Low.
Neuropathic pain, fibromyalgia, OCD (augmentation): Small studies with inconsistent results; not routinely recommended. Evidence quality: Low to Very Low.
Autism spectrum disorder (paediatric): Two controlled trials (n = 578) in children aged 6–12 years failed to demonstrate efficacy. Not recommended.
Memantine Dosing
Dosing by Clinical Scenario
| Clinical Scenario | Starting Dose | Maintenance Dose | Maximum Dose | Notes |
|---|---|---|---|---|
| Moderate-to-severe AD — IR tablet initiation | 5 mg once daily | 10 mg BID (20 mg/day) | 10 mg BID (20 mg/day) | Titrate in 5 mg increments: 5 mg QD → 5 mg BID → 5 mg AM + 10 mg PM → 10 mg BID; minimum 1 week between increases May be taken with or without food |
| Moderate-to-severe AD — XR capsule initiation | 7 mg once daily | 28 mg once daily | 28 mg once daily | Titrate in 7 mg increments weekly: 7 → 14 → 21 → 28 mg/day XR capsules may be opened and sprinkled on applesauce |
| Add-on to stable AChE inhibitor (donepezil) | 5 mg QD (IR) or 7 mg QD (XR) | 20 mg/day (IR) or 28 mg/day (XR) | Same as monotherapy | No dose adjustment needed for either drug; memantine does not affect donepezil PK or vice versa Study 2 demonstrated benefit of adding memantine to donepezil (FDA PI) |
| Switching from IR to XR | IR 10 mg BID (20 mg/day) → XR 28 mg QD the following day | 28 mg/day | Begin XR the day after the last IR dose | |
| Treatment interruption — restart | 5 mg QD (IR) or 7 mg QD (XR) | Re-titrate to target | Same as original target | If missed several days, resume at lower doses and re-titrate |
Special Population Adjustments
| Clinical Scenario | Starting Dose | Maintenance Dose | Maximum Dose | Notes |
|---|---|---|---|---|
| Severe renal impairment (CrCl 5–29 mL/min) | 5 mg QD (IR) | 5 mg BID (10 mg/day) or 14 mg/day (XR) | 10 mg/day (IR) or 14 mg/day (XR) | AUC increased ~115%, t½ nearly doubled; reduce target dose by 50% |
| Mild–moderate renal impairment | No adjustment needed | AUC increased only 4–60%; standard doses appropriate | ||
| Mild–moderate hepatic impairment | No adjustment needed | No change in exposure (moderate impairment); t½ increased ~16% | ||
| Severe hepatic impairment | Use with caution; not studied | Minimal hepatic metabolism, but no safety data in this population | ||
Memantine has a remarkably favourable tolerability profile compared with cholinesterase inhibitors. In pooled controlled trials, the discontinuation rate due to adverse events was the same in the memantine group (10.1%) as in the placebo group (11.5%), and no individual adverse reaction led to discontinuation in 1% or more of memantine-treated patients at a rate exceeding placebo. This makes memantine one of the best-tolerated CNS drugs in elderly patients and is a key advantage over the GI-intolerance-prone cholinesterase inhibitors.
Pharmacology
Mechanism of Action
In Alzheimer’s disease, chronic pathological overactivation of NMDA-type glutamate receptors by tonically elevated glutamate levels contributes to excitotoxic neuronal damage and symptom progression. Memantine is a low-to-moderate affinity, uncompetitive (open-channel) NMDA receptor antagonist that binds preferentially to NMDA receptor-operated cation channels. Its voltage-dependent kinetics and rapid off-rate allow it to block pathological tonic activation of NMDA receptors while preserving normal phasic synaptic signalling necessary for learning and memory. This “gentle blockade” contrasts with high-affinity NMDA antagonists (e.g., ketamine, MK-801), which impair physiological neurotransmission. Memantine also exhibits antagonistic activity at the 5-HT3 receptor and weak blockade of nicotinic acetylcholine receptors, though the clinical relevance of these secondary actions at therapeutic doses is uncertain. There is no evidence that memantine prevents or slows the underlying neurodegeneration.
ADME Profile
| Parameter | Value | Clinical Implication |
|---|---|---|
| Absorption | Complete absorption; bioavailability ~100%; Tmax 3–7 h (IR), 9–12 h (XR); food has no effect on absorption; linear PK over therapeutic range | Can be taken with or without food; reliable oral delivery regardless of feeding status |
| Distribution | Vd 9–11 L/kg; plasma protein binding 45%; crosses BBB readily (CSF/serum ratio ~0.52); widely distributed to tissues | Large Vd indicates extensive tissue penetration; low-moderate protein binding makes displacement interactions unlikely |
| Metabolism | Partial hepatic metabolism (not via CYP450); ~48% excreted unchanged in urine; metabolites (N-glucuronide, 6-hydroxy memantine, 1-nitroso-deaminated memantine) have minimal NMDA antagonist activity | CYP450-independent metabolism confers an exceptionally low drug interaction potential; no dose adjustment needed for hepatic impairment (mild–moderate) |
| Elimination | t½ 60–80 h; predominantly renal; active tubular secretion moderated by pH-dependent tubular reabsorption; clearance reduced ~80% at urine pH 8; 74% of dose excreted as parent + N-glucuronide conjugate | Very long half-life supports once-daily XR dosing and provides stable plasma levels; alkaline urine markedly reduces clearance — critical interaction with urine-alkalinising conditions |
Side Effects
Memantine is among the best-tolerated treatments for Alzheimer’s disease. Adverse reaction data below are from eight pooled, double-blind, placebo-controlled trials (FDA PI Table 1; n = 940 memantine vs n = 922 placebo; treatment up to 28 weeks). The overall discontinuation rate due to adverse events was identical to placebo (10.1% vs 11.5%).
| Adverse Effect | Incidence | Clinical Note |
|---|---|---|
| Dizziness | 7% (vs 5% placebo) | Most frequently reported; usually transient during titration |
| Headache | 6% (vs 3% placebo) | Mild; does not typically require treatment discontinuation |
| Confusion | 6% (vs 5% placebo) | Difficult to distinguish from disease progression; evaluate if new-onset |
| Constipation | 5% (vs 3% placebo) | Encourage adequate fluid intake and dietary fibre; rule out anticholinergic burden |
| Adverse Effect | Incidence | Clinical Note |
|---|---|---|
| Hypertension | 4% (vs 2% placebo) | Monitor blood pressure at each visit; clinical significance modest |
| Coughing | 4% (vs 3% placebo) | Non-specific; evaluate for respiratory infection in elderly population |
| Pain | 3% (vs 1% placebo) | Unspecified body pain; assess for musculoskeletal or other causes |
| Back pain | 3% (vs 2% placebo) | Common in elderly; unlikely drug-related but recorded as treatment-emergent |
| Vomiting | 3% (vs 2% placebo) | Much lower incidence than cholinesterase inhibitors (20–47%) |
| Somnolence | 3% (vs 2% placebo) | Advise caution with driving; may compound cognitive slowing |
| Hallucination | 3% (vs 2% placebo) | May also reflect disease progression; evaluate triggers and onset |
| Fatigue | 2% (vs 1% placebo) | Generally mild; assess functional impact |
| Dyspnea | 2% (vs 1% placebo) | Evaluate for cardiac or pulmonary causes in elderly patients |
| Adverse Effect | Estimated Frequency | Typical Onset | Required Action |
|---|---|---|---|
| Stevens-Johnson syndrome | Very rare (post-marketing) | Variable | Discontinue immediately; emergency dermatological care; do not rechallenge |
| Agranulocytosis / pancytopenia / TTP | Very rare (post-marketing) | Variable | Urgent FBC; haematology referral; discontinue memantine |
| Congestive cardiac failure | Rare (post-marketing) | Variable | Cardiac evaluation; manage per standard heart failure guidelines |
| Hepatitis | Rare (post-marketing) | Variable | Check LFTs; discontinue if hepatitis confirmed |
| Acute renal failure | Rare (post-marketing) | Variable | Monitor renal function; hold memantine; evaluate for reversible causes |
| Suicidal ideation | Very rare (post-marketing) | Variable | Psychiatric assessment; ensure safe environment; consider discontinuation |
| Seizures | 0.2% (vs 0.5% placebo) | Any time | Lower rate than placebo in trials; evaluate independently from memantine; seizures may reflect AD progression |
Unlike cholinesterase inhibitors, memantine does not cause significant nausea, vomiting, or diarrhoea. It lacks the cholinergic GI effects that drive much of the treatment discontinuation seen with donepezil, rivastigmine, and galantamine. This makes it particularly suitable for frail elderly patients or those who have failed cholinesterase inhibitor therapy due to GI intolerance.
Drug Interactions
Memantine has an exceptionally clean drug interaction profile. It does not inhibit or induce any CYP450 isoenzyme and does not affect the pharmacokinetics of warfarin, bupropion, donepezil, or metformin. Its primary interaction risk is pharmacokinetic: because ~48% is excreted unchanged by renal tubular secretion, drugs or conditions that alkalinise urine can dramatically reduce memantine clearance (up to 80% reduction at pH 8).
Monitoring
- Cognitive functionBaseline, then every 3–6 months
RoutineUse SIB (for moderate-severe) or MMSE/MoCA. Memantine targets functional stabilisation rather than cognitive improvement; reassess if progressive decline despite treatment. - Renal functionBaseline, then annually or if clinical change
RoutineTarget dose must be halved in severe renal impairment (CrCl 5–29 mL/min). Long half-life (60–80 h) means accumulation occurs slowly; reassess dose if renal function declines. - Urine pHAs clinically indicated
Trigger-basedClearance drops ~80% at pH 8. Assess in patients with recurrent UTIs, renal tubular acidosis, drastic dietary changes, or concurrent use of carbonic anhydrase inhibitors or sodium bicarbonate. - Blood pressureEach visit
RoutineHypertension was reported in 4% vs 2% placebo. Monitor at each visit, especially in patients with pre-existing cardiovascular disease. - Neuropsychiatric symptomsEach visit
RoutineHallucinations (3%), confusion (6%), and somnolence (3%) may occur. Differentiate drug-related effects from disease progression. Post-marketing reports of suicidal ideation warrant vigilance. - Bowel functionEach visit during titration
RoutineConstipation (5%) is more common than with placebo. Ensure adequate hydration and fibre; especially relevant in patients already taking anticholinergic medications.
Contraindications & Cautions
Absolute Contraindications
- Known hypersensitivity to memantine hydrochloride or any excipient in the formulation
Relative Contraindications (Specialist Input Recommended)
- Severe renal impairment (CrCl 5–29 mL/min): Dose must be halved; monitor closely for accumulation
- Conditions that alkalinise urine: Renal tubular acidosis, severe UTIs, chronic use of carbonic anhydrase inhibitors or sodium bicarbonate; clearance may drop by up to 80%
- Severe hepatic impairment: Not studied; use with caution
Use with Caution
- History of seizures: Seizure incidence in trials was lower on memantine (0.2%) than placebo (0.5%), but theoretical risk remains; monitor
- Cardiovascular disease: Hypertension reported at higher rate; post-marketing cases of congestive cardiac failure
- Concurrent use of other NMDA antagonists: Amantadine, ketamine, dextromethorphan; additive CNS effects possible
- Genitourinary conditions: Conditions affecting urine pH or renal tubular function may alter memantine clearance
The clearance of memantine is reduced by approximately 80% under alkaline urine conditions (pH 8). Drugs such as carbonic anhydrase inhibitors and sodium bicarbonate, clinical states such as renal tubular acidosis and severe urinary tract infections, and drastic dietary changes (e.g., shift to a vegetarian diet) can alkalinise urine and lead to memantine accumulation with increased risk of adverse effects. Clinicians should be aware of this pharmacokinetic vulnerability when prescribing memantine to patients with any of these risk factors.
Patient Counselling
Purpose of Therapy
Memantine is prescribed to help manage the symptoms of moderate-to-severe Alzheimer’s disease. It works differently from other Alzheimer’s medicines (such as donepezil) by blocking a chemical in the brain called glutamate that, when overactive, can damage nerve cells. Memantine does not cure Alzheimer’s disease or stop it from getting worse, but it may help maintain daily functioning and slow the worsening of symptoms. It can be taken alongside other Alzheimer’s medicines.
How to Take
IR tablets: Take twice daily with or without food. XR capsules: Take once daily. Swallow whole, or open and sprinkle on applesauce then swallow immediately without chewing. Oral solution: Measure dose using the provided dosing device.
Sources
- Namenda (memantine hydrochloride) tablets — FDA-approved Prescribing Information. Allergan (AbbVie). Revised November 2018. accessdata.fda.govPrimary source for IR tablet dosing, adverse reactions (Table 1, pooled n=1,862), pharmacokinetics, drug interactions, and clinical trial data (Studies 1–3).
- Namenda XR (memantine hydrochloride) extended-release capsules — FDA-approved Prescribing Information. Revised 2014. accessdata.fda.govSource for XR capsule dosing, PK of extended-release formulation, renal dose adjustment (14 mg/day target for severe impairment), and paediatric ASD study data.
- Reisberg B, Doody R, Stöffler A, Schmitt F, Ferris S, Möbius HJ; Memantine Study Group. Memantine in moderate-to-severe Alzheimer’s disease. N Engl J Med. 2003;348(14):1333–1341. doi:10.1056/NEJMoa013128Landmark 28-week RCT (Study 1, n=252) demonstrating significant benefit on SIB (+5.7 points) and ADCS-ADL (+3.4 points) in moderate-to-severe AD.
- Tariot PN, Farlow MR, Grossberg GT, Graham SM, McDonald S, Gergel I; Memantine Study Group. Memantine treatment in patients with moderate to severe Alzheimer disease already receiving donepezil: a randomized controlled trial. JAMA. 2004;291(3):317–324. doi:10.1001/jama.291.3.317Pivotal 24-week add-on trial (Study 2, n=404) showing benefit of adding memantine to stable donepezil; SIB +3.3, ADCS-ADL +1.6 points vs placebo/donepezil.
- Winblad B, Poritis N. Memantine in severe dementia: results of the 9M-Best Study (benefit and efficacy in severely demented patients during treatment with memantine). Int J Geriatr Psychiatry. 1999;14(2):135–146. doi:10.1002/(SICI)1099-1166(199902)14:2<135::AID-GPS906>3.0.CO;2-012-week Latvian study (Study 3, n=166) in severe dementia showing significant benefit on BGP care dependency and CGI-C.
- Peskind ER, Potkin SG, Pomara N, et al. Memantine treatment in mild to moderate Alzheimer disease: a 24-week randomized, controlled trial. Am J Geriatr Psychiatry. 2006;14(8):704–715. doi:10.1097/01.JGP.0000224350.82719.8324-week RCT examining memantine in mild-to-moderate AD; showed significant benefit on ADAS-cog but not CIBIC-plus.
- van Dyck CH, Schmitt FA, Olin JT. A responder analysis of memantine treatment in patients with Alzheimer disease maintained on donepezil. Am J Geriatr Psychiatry. 2006;14(5):428–437. doi:10.1097/01.JGP.0000203151.17311.38Responder analysis of the Tariot 2004 trial; characterises clinical response patterns in combination therapy.
- National Institute for Health and Care Excellence (NICE). Dementia: assessment, management, and support for people living with dementia and their carers. NICE guideline [NG97]. 2018 (updated 2023). nice.org.uk/guidance/ng97UK guideline recommending memantine for moderate-to-severe AD, including in combination with an AChE inhibitor.
- Lipton SA. Paradigm shift in neuroprotection by NMDA receptor blockade: memantine and beyond. Nat Rev Drug Discov. 2006;5(2):160–170. doi:10.1038/nrd1958Seminal review of memantine’s uncompetitive, open-channel NMDA antagonism and the concept of preserving physiological signalling while blocking excitotoxicity.
- Parsons CG, Stöffler A, Danysz W. Memantine: a NMDA receptor antagonist that improves memory by restoration of homeostasis in the glutamatergic system — too little activation is bad, too much is even worse. Neuropharmacology. 2007;53(6):699–723. doi:10.1016/j.neuropharm.2007.07.013Comprehensive review of memantine pharmacology covering receptor kinetics, selectivity, and dose-response relationships.
- Noetzli M, Eap CB. Pharmacodynamic, pharmacokinetic and pharmacogenetic aspects of drugs used in the treatment of Alzheimer’s disease. Clin Pharmacokinet. 2013;52(4):225–241. doi:10.1007/s40262-013-0038-9PK review covering memantine absorption, distribution, renal elimination, pH-dependent clearance, and renal impairment dose adjustments.