What precautions and contraindications should be considered when initiating memantine (NMDA‑receptor antagonist) therapy for a patient with moderate to severe Alzheimer’s disease?

Precautions and Contraindications for Initiating Memantine

Major contraindications to memantine include uncontrolled asthma, angle-closure glaucoma, sick sinus syndrome, and left bundle-branch block; these must be ruled out before starting therapy. 1, 2

Absolute Contraindications

• Known hypersensitivity to memantine hydrochloride or any formulation excipients 3
• Uncontrolled asthma – memantine should not be initiated in patients with active, poorly controlled asthma 1, 2
• Angle-closure glaucoma – contraindicated due to potential worsening of intraocular pressure 1, 2
• Sick sinus syndrome – risk of cardiac conduction abnormalities 1, 2
• Left bundle-branch block – cardiac conduction concerns preclude use 1, 2

Renal Function Assessment

Severe renal impairment requires dose reduction to 5 mg twice daily (rather than the standard 10 mg twice daily maintenance dose). 3 Before initiating memantine:

• Obtain baseline serum creatinine and calculate creatinine clearance 3
• Adjust dosing in patients with creatinine clearance <30 mL/min 3

Urinary pH Considerations

Conditions that raise urine pH may decrease urinary elimination of memantine, resulting in increased plasma levels and potential toxicity. 3 Be cautious with:

• Renal tubular acidosis 3
• Severe urinary tract infections with urease-producing organisms 3
• Concurrent medications that alkalinize urine (e.g., carbonic anhydrase inhibitors, sodium bicarbonate) 3

Common Adverse Effects to Monitor

The most frequent adverse reactions (≥5% and greater than placebo) include:

• Dizziness – most common, counsel patients about fall risk 3
• Headache 3
• Confusion – particularly important to distinguish from disease progression 3
• Constipation 3

Gastrointestinal symptoms and dizziness are typical, though memantine is generally better tolerated than cholinesterase inhibitors. 4

Cardiovascular Screening

Before initiation, assess for:

• Cardiac conduction abnormalities via ECG if history suggests risk 1, 2
• Bradycardia or heart block – particularly in patients on concurrent cholinesterase inhibitors 1

Drug Interactions

Concurrent use with other NMDA antagonists (e.g., amantadine, ketamine, dextromethorphan) should be avoided due to additive effects and increased risk of adverse events. 3

Fall Risk Assessment

Memantine does not increase fall risk in clinical trial populations, unlike some cholinesterase inhibitors. 5 However, dizziness is common, so:

• Assess baseline fall risk and home safety 3
• Counsel caregivers about monitoring during dose titration 3

Dosing Titration Requirements

Start at 5 mg once daily and increase in 5 mg increments with a minimum of 1 week between dose increases to reach the maintenance dose of 10 mg twice daily. 3 This gradual titration minimizes adverse effects, particularly dizziness and confusion. 3

Monitoring for Therapeutic Response

A beneficial effect, if present, should be observable within 3 months of starting treatment, manifesting as either cognitive improvement or stabilization. 1, 2 If no benefit is observed by 3 months or the patient continues to decline without measurable improvement, discontinuation should be considered. 1, 2

Special Population Considerations

• Moderate to severe Alzheimer disease is the FDA-approved indication 3
• Mild vascular dementia has shown some benefit, though memantine is not well-studied in mild Alzheimer disease 1
• Parkinson disease dementia remains investigational with insufficient evidence for routine use 2

Combination Therapy Safety

Memantine is well tolerated as monotherapy and in combination with donepezil or other cholinesterase inhibitors. 4 When combining:

• Monitor for additive adverse effects, particularly gastrointestinal symptoms from the cholinesterase inhibitor 4
• The combination may provide additional benefits across multiple domains compared to cholinesterase inhibitor monotherapy 4, 6