What are the prescribing protocols, monitoring requirements, and potential side effects and adverse reactions for cholinesterase inhibitors (donepezil, rivastigmine, galantamine) and memantine in older adults with dementia?

Prescribing Protocols for Dementia Medications

Base your decision to initiate cholinesterase inhibitors or memantine on individualized assessment of benefits versus harms, as these medications produce statistically significant but clinically marginal improvements in cognition and global function 1.

Cholinesterase Inhibitors (Donepezil, Rivastigmine, Galantamine)

Indications and Dosing

Donepezil:

• FDA-approved for mild to moderate and moderate to severe Alzheimer's disease 2
• Start at 5 mg once daily
• May increase to 10 mg once daily after 4-6 weeks
• For moderate to severe disease, can increase to 23 mg once daily 2
• Take with or without food

Rivastigmine:

• Oral: Start 1.5 mg twice daily, titrate by 1.5 mg increments every 2-4 weeks
• Maximum: 6 mg twice daily (12 mg/day total)
• Transdermal patch causes fewer gastrointestinal side effects than oral formulation 3

Galantamine:

• Start 4 mg twice daily or 8 mg extended-release once daily
• Titrate every 4 weeks
• Target dose: 16-24 mg daily 1

Monitoring Requirements

Assess response within 3 months of initiation - any beneficial effect (improvement or stabilization) should be observed by this timeframe based on trial durations 1. If no benefit is observed or the patient continues to decline and slowing decline is no longer a goal, discontinue treatment 1.

Monitor for:

• Cardiovascular effects: Cholinesterase inhibitors may cause vagotonic effects manifesting as bradycardia or heart block 2. Check baseline heart rate and rhythm, particularly in patients with cardiac conduction abnormalities.
• Gastrointestinal symptoms: Observe closely at initiation and after dose increases for nausea and vomiting 2
• Weight: Particularly with donepezil 23 mg, which is associated with weight loss 2
• Gastrointestinal bleeding risk: Monitor patients at increased risk for ulcers 2

Contraindications

Major contraindications include 1:

• Uncontrolled asthma or obstructive pulmonary disease
• Angle-closure glaucoma
• Sick sinus syndrome
• Left bundle-branch block
• Known hypersensitivity to the drug or piperidine derivatives (for donepezil) 2

Side Effects and Adverse Reactions

Most common adverse events (9-12% in treatment groups) 1:

• Nausea and vomiting (most frequent)
• Diarrhea
• Dizziness
• Headache
• Agitation
• Muscle cramps
• Fatigue
• Anorexia

Comparative tolerability: Rivastigmine has higher rates of nausea during titration and maintenance phases compared to donepezil, with more overall adverse events but no difference in serious events 1. Galantamine shows marginally higher adverse event rates than donepezil 1. In clinical practice, 43.5% of cholinesterase inhibitor recipients experienced at least one adverse event, with 37% being gastrointestinal 4.

Serious considerations:

• May exaggerate succinylcholine-type muscle relaxation during anesthesia 2
• May cause bladder outflow obstruction 2
• Potential to cause generalized convulsions 2

Memantine

Indications and Dosing

FDA-approved for moderate to severe Alzheimer's disease 1, 5. Also shows mild benefit in mild to moderate vascular dementia 1.

Dosing schedule 5:

• Week 1: 5 mg once daily
• Week 2: 5 mg twice daily (10 mg/day)
• Week 3: 15 mg/day (5 mg + 10 mg in separate doses)
• Week 4 and beyond: 10 mg twice daily (20 mg/day target dose)
• Minimum interval between dose increases: 1 week
• Take with or without food

Renal impairment: Target dose of 5 mg twice daily (10 mg/day) in severe renal impairment (creatinine clearance 5-29 mL/min) 5

Hepatic impairment: Use with caution in severe hepatic impairment 5

Monitoring Requirements

Assess response within 3 months - consistent with cholinesterase inhibitor monitoring 1.

Monitor for:

• Urine pH: Alkaline urine conditions decrease memantine clearance by approximately 80%, potentially leading to drug accumulation 5. Be cautious with carbonic anhydrase inhibitors, sodium bicarbonate, renal tubular acidosis, or severe urinary tract infections.
• Renal function: Particularly in patients with renal impairment
• Adverse events: Generally better tolerated than cholinesterase inhibitors

Contraindications

• Known hypersensitivity to memantine or excipients 5
• Use caution with conditions that raise urine pH 5

Side Effects and Adverse Reactions

Most common adverse events (≥5% and higher than placebo) 5:

• Dizziness
• Headache
• Confusion
• Constipation

Discontinuation rates: 10.1% in memantine group versus 11.5% in placebo group - no significant difference 5. In clinical practice, only 12.5% of memantine recipients developed adverse events, significantly lower than the 43.5% seen with cholinesterase inhibitors 4.

Postmarketing serious adverse reactions (rare) 5:

• Blood disorders: agranulocytosis, leukopenia, pancytopenia, thrombocytopenia
• Cardiac: congestive heart failure
• Gastrointestinal: pancreatitis
• Hepatobiliary: hepatitis
• Psychiatric: suicidal ideation
• Renal: acute renal failure
• Skin: Stevens-Johnson syndrome

Seizures: Occurred in 0.2% of memantine-treated patients versus 0.5% of placebo patients 5

Drug Selection Algorithm

Choose based on tolerability, adverse effect profile, ease of use, and cost - evidence is insufficient to demonstrate superiority of one agent over another 1.

1. For mild to moderate Alzheimer's disease: Start with donepezil 5 mg or 10 mg daily (ranked first for cognitive benefit in network meta-analysis, though third for adverse events) 6, or galantamine 16-24 mg daily (ranked second for both benefit and harm) 6

2. For moderate to severe Alzheimer's disease: Use memantine 20 mg daily, which shows significant cognitive and functional improvements 7. May combine with cholinesterase inhibitor, though evidence for added benefit is mixed 3

3. For vascular dementia: Cholinesterase inhibitors are conditionally recommended 7. Memantine shows mild benefit in mild vascular dementia 1

4. For Lewy body dementia: Cholinesterase inhibitors are strongly recommended 7

5. For Parkinson's disease dementia: Cholinesterase inhibitors are conditionally recommended 7

Critical Prescribing Pitfalls

• Avoid tacrine: Severe side effects make it an unreasonable choice 1
• Do not prescribe routinely to all dementia patients: Benefits are modest and not clinically significant for many patients 1
• Reassess at 3 months: If no stabilization or improvement occurs, discontinue 1
• Watch for drug interactions: 41.3% of patients in clinical practice had concomitant use of interacting drugs 4
• Avoid combining with other NMDA antagonists (amantadine, ketamine, dextromethorphan) without careful consideration 5
• Titrate slowly: Average prescribed daily doses in practice are often lower than effective defined daily doses 4

Evidence Quality Note

The evidence shows statistically significant but clinically marginal improvements in cognition and global assessment 8, 1. Most trials were short duration (≤6 months), limiting ability to detect delay in disease progression 8. The clinical importance of small effect sizes (donepezil 10 mg: -2.21 ADAS-Cog points; galantamine: -2.01 points) remains questionable 8. However, in the absence of other treatments, patients may still wish to consider these agents 6.