What are the indications and dosing guidelines for amantadine?

Amantadine: Indications and Dosing Guidelines

Amantadine is primarily indicated for prophylaxis and treatment of influenza A virus infection and for the treatment of Parkinson's disease, with specific dosing requirements based on age, weight, and renal function. 1

Indications

1. Influenza A

• Prophylaxis: Prevention of signs and symptoms of influenza A virus infection

  • 70-90% effective in preventing illness from influenza A infection 2
  • Allows subclinical infection and development of protective antibody against circulating viruses
  • Should be taken daily during influenza activity in the community

• Treatment: For uncomplicated respiratory tract illness caused by influenza A virus strains

  • Most effective when administered early in the course of illness
  • Should be discontinued after 3-5 days of treatment or within 24-48 hours after symptoms disappear 2

2. Parkinson's Disease/Syndrome

• Treatment of:
  • Idiopathic Parkinson's disease
  • Postencephalitic parkinsonism
  • Symptomatic parkinsonism following carbon monoxide intoxication
  • Parkinsonism in elderly patients with cerebral arteriosclerosis 1
  • Note: Less effective than levodopa for Parkinson's disease

3. Drug-induced Extrapyramidal Reactions

• Management of medication-induced movement disorders 1

Dosing Guidelines

Children

• Under 1 year: Not adequately evaluated, not recommended
• 1-9 years: FDA-approved dosage is 4.4-8.8 mg/kg/day (not exceeding 150 mg/day)
  • Recommended dose: 5 mg/kg/day to reduce toxicity risk 2
• 10+ years:
  • If ≥40 kg: 200 mg/day (100 mg twice daily)
  • If <40 kg: 5 mg/kg/day regardless of age 2

Adults (13-64 years)

• Influenza treatment/prophylaxis: 200 mg/day (100 mg twice daily) 2

Elderly (≥65 years)

• Maximum daily dose: 100 mg/day (not exceeding)
• Rationale: Renal function declines with age 2
• Further dose reduction may be necessary for some elderly patients

Patients with Impaired Renal Function

• Creatinine clearance <50 mL/min/1.73m²: Dose reduction required
• Consult package insert for specific dosing recommendations based on creatinine clearance
• Monitor carefully for adverse reactions
• Hemodialysis contributes minimally to amantadine clearance 2

Administration Duration

• For influenza treatment: 3-5 days or until 24-48 hours after symptoms disappear 2
• For influenza prophylaxis: Daily during influenza activity in the community
  • A more cost-effective approach is to take only during peak activity periods 2

Side Effects and Precautions

• Common side effects: Central nervous system effects (nervousness, anxiety, insomnia, difficulty concentrating) and gastrointestinal effects
• Side effects are usually mild and resolve after discontinuation 2
• CNS side effects are more common with amantadine than rimantadine
• Careful monitoring needed in patients with:
  • Renal dysfunction
  • Liver disease
  • Seizure disorders
  • Elderly patients

Important Clinical Considerations

• Amantadine is not a substitute for influenza vaccination 1
• Influenza viruses may develop resistance mutations that decrease drug effectiveness
• No evidence that amantadine prevents development of influenza A pneumonitis or other complications in high-risk patients
• Not effective for viral respiratory illnesses other than those caused by influenza A virus strains 1

Dosage Forms

• Available in oral formulations (capsules) from which it is well absorbed and widely distributed 1