What is amantadine used for?

Uses of Amantadine

Amantadine is primarily indicated for the treatment of Parkinson's disease, drug-induced extrapyramidal reactions, and historically for influenza A prophylaxis and treatment, though it is no longer recommended for influenza due to widespread viral resistance. 1

Primary Indications

1. Parkinson's Disease

• Indicated for idiopathic Parkinson's disease
• Effective for postencephalitic parkinsonism
• Used for symptomatic parkinsonism following carbon monoxide intoxication
• Beneficial in elderly patients with parkinsonism associated with cerebral arteriosclerosis 1
• Note: Less effective than levodopa for Parkinson's disease treatment

2. Drug-Induced Extrapyramidal Reactions

• Effectively treats drug-induced extrapyramidal reactions
• Has fewer anticholinergic side effects compared to traditional anticholinergic antiparkinson drugs 1

3. Historical Use for Influenza A (No Longer Recommended)

• Previously indicated for prophylaxis and treatment of influenza A virus infections 2, 1
• When effective (pre-resistance), amantadine:
  • Reduced duration of fever and systemic symptoms
  • Was 70-90% effective in preventing illness when used prophylactically 2
  • Was most effective when administered within 48 hours of symptom onset 2

Current Status for Influenza Treatment

Amantadine is no longer recommended for influenza treatment or prophylaxis due to:

• Widespread resistance among circulating influenza A viruses 2, 3
• CDC reported that 92% of influenza A (H3N2) viruses demonstrated resistance to adamantanes by 2005-2006 2
• The Advisory Committee on Immunization Practices (ACIP) recommends against using amantadine for influenza until susceptibility is reestablished 2, 3
• Neuraminidase inhibitors (oseltamivir, zanamivir) have replaced adamantanes as first-line agents 3

Pharmacokinetic Considerations

• Well absorbed orally and widely distributed throughout the body 4
• Primarily eliminated through renal clearance via glomerular filtration and tubular secretion 5, 4
• Half-life in normal renal function: approximately 11.8 hours 5
• Half-life in renal impairment: can extend from 18.5 hours to 33.8 days depending on severity 5
• Dose adjustments required in patients with renal dysfunction to prevent toxicity 5, 4

Side Effects and Safety Concerns

• CNS side effects occur in 5-10% of healthy young adults at standard doses (200 mg/day) 2
  • Nervousness, anxiety, insomnia, difficulty concentrating, lightheadedness
  • More severe in elderly patients (confusion, dizziness, ataxia) 2
• Gastrointestinal side effects: anorexia and nausea 2
• Higher incidence of CNS side effects compared to rimantadine 2, 3
• Dose reduction to ≤100 mg/day may reduce side effect frequency without compromising efficacy 2

Important Considerations for Clinical Use

• Dosage should be adjusted based on:

  • Patient's age and weight
  • Renal function
  • Presence of neuropsychiatric disorders
  • Concomitant use of psychotropic drugs
  • History of seizures 2

• Amantadine is contraindicated or requires special caution in:

  • Patients with severe renal impairment
  • Elderly patients with increased risk of CNS effects
  • Patients with history of seizures or psychiatric disorders

Conclusion

While amantadine was historically valuable for influenza A management, its current clinical utility is primarily limited to Parkinson's disease and drug-induced extrapyramidal reactions due to widespread viral resistance. When prescribing amantadine, clinicians should carefully consider patient-specific factors, particularly renal function and neuropsychiatric history.