What is the dosing for Symmetrel (amantadine)?

Amantadine (Symmetrel) Dosing Guidelines

For adults, the standard dosage of amantadine (Symmetrel) is 200 mg daily, given either as a single daily dose or divided into 100 mg twice daily; however, dosage must be adjusted based on age, renal function, and indication. 1

Adult Dosing

For Influenza A Treatment and Prophylaxis:

• Standard adult dose: 200 mg daily (single dose or 100 mg twice daily)
• Adults ≥65 years: 100 mg daily due to age-related decline in renal function 2, 1
• Duration:
  • Treatment: Continue for 24-48 hours after symptom resolution
  • Prophylaxis: At least 10 days following known exposure 1

For Parkinson's Disease:

• Initial dose: 100 mg daily, especially in patients with serious medical conditions
• Maintenance dose: 100 mg twice daily (200 mg/day total)
• Maximum dose: May increase to 300-400 mg daily in divided doses under close supervision if needed 1
• Long-term management: Temporary discontinuation may help regain effectiveness if benefit diminishes after several months 1

Pediatric Dosing

For Influenza A Treatment and Prophylaxis:

• Children 1-9 years: 5-8 mg/kg/day (not to exceed 150 mg/day), given as single daily dose or divided into two doses 2
• Children 9-12 years: 200 mg daily, given as 100 mg twice daily 2, 1
• Children <1 year: Not adequately evaluated, use not recommended 2

Dosage Adjustments for Special Populations

Renal Impairment:

• Creatinine clearance 30-50 mL/min: 200 mg first day, then 100 mg daily
• Creatinine clearance 15-29 mL/min: 200 mg first day, then 100 mg on alternate days
• Creatinine clearance <15 mL/min: 200 mg every 7 days
• Hemodialysis patients: 200 mg every 7 days 1

Elderly Patients:

• Maximum 100 mg daily for persons ≥65 years due to decreased renal function 2, 1
• Elderly patients are at higher risk for CNS side effects including visual hallucinations and delirium 3

Administration Considerations

• If CNS side effects develop with once-daily dosing, splitting the dose may reduce complaints 1
• When used with levodopa, maintain amantadine at 100 mg once or twice daily while gradually increasing levodopa to optimal benefit 1
• For drug-induced extrapyramidal reactions, the usual dose is 100 mg twice daily 1

Important Precautions

• Monitor closely for CNS side effects, especially in elderly patients 3
• Amantadine should not be used as primary therapy for influenza due to rapid emergence of resistance 2
• Patients with congestive heart failure, peripheral edema, orthostatic hypotension, or impaired renal function require dose reduction 1
• Avoid combination with anticholinergic agents in elderly patients due to increased risk of delirium 3

Common Pitfalls to Avoid

1. Failing to adjust dosage for renal impairment, which can lead to drug accumulation and toxicity 4
2. Not recognizing early signs of CNS toxicity, especially in elderly patients
3. Using standard adult dosing in elderly patients instead of the recommended reduced dose of 100 mg daily
4. Continuing treatment beyond recommended duration, especially for influenza treatment

Remember that amantadine has a logarithmic increase in plasma concentration as a function of dose, making appropriate dosing particularly important to avoid toxicity 4.