What is the use and dosage of Amantadine for influenza A and Parkinson's disease?

Amantadine Use and Dosage for Influenza A and Parkinson's Disease

Amantadine is indicated for prophylaxis and treatment of influenza A virus infection, as well as for the treatment of Parkinson's disease and drug-induced extrapyramidal reactions, with specific dosing requirements for each indication based on patient age and renal function. 1

Influenza A

Prophylaxis and Treatment

• Amantadine is effective for both prevention (70-90% effective) and treatment of influenza A virus infection 2
• For treatment, amantadine should be started within 24-48 hours of symptom onset to reduce severity and duration of illness 2
• Treatment should continue for 24-48 hours after symptoms disappear 2
• For prophylaxis, amantadine should be continued for at least 10 days following known exposure 1

Adult Dosing for Influenza A

• Standard adult dose: 200 mg daily (can be given as single dose or 100 mg twice daily) 1
• For adults ≥65 years: 100 mg daily due to age-related decline in renal function 2
• Split dosing (100 mg twice daily) may reduce CNS side effects 1

Pediatric Dosing for Influenza A

• Children 1-9 years: 5 mg/kg/day (not to exceed 150 mg/day) 2
• Children 10-12 years: 200 mg/day (100 mg twice daily) 2
• For children weighing <40 kg: 5 mg/kg/day regardless of age 2

Parkinson's Disease

Adult Dosing for Parkinson's Disease

• Initial dose: 100 mg twice daily when used alone 1
• For patients with serious medical illnesses or those on other antiparkinson drugs: start with 100 mg daily 1
• May increase to 300-400 mg daily in divided doses if needed, with close supervision 1
• Onset of action typically within 48 hours 1

Concomitant Therapy

• When used with levodopa: maintain amantadine at 100 mg once or twice daily while gradually increasing levodopa to optimal benefit 1
• May help smooth out fluctuations in improvement seen with levodopa alone 1

Drug-Induced Extrapyramidal Reactions

• Standard dose: 100 mg twice daily 1
• May increase to 300 mg daily in divided doses if needed 1

Dosage Adjustments for Renal Impairment

Amantadine is primarily excreted unchanged in urine (90% of ingested dose) and requires dose adjustment in renal impairment 3, 4:

• Creatinine clearance 30-50 mL/min: 200 mg first day, then 100 mg daily thereafter 1
• Creatinine clearance 15-29 mL/min: 200 mg first day, then 100 mg on alternate days 1
• Creatinine clearance <15 mL/min: 200 mg every 7 days 1
• Hemodialysis patients: 200 mg every 7 days (hemodialysis removes <5% of the drug) 1, 3

Side Effects and Monitoring

Common Side Effects

• CNS side effects (5-10% of patients): nervousness, insomnia, difficulty concentrating, lightheadedness 2
• Gastrointestinal effects: anorexia, nausea 2
• Side effects often diminish after the first week of use 2

Special Considerations

• More serious CNS effects (confusion, seizures) occur primarily in elderly, those with renal disease, or seizure disorders 2
• Elderly patients may experience more severe CNS side effects and higher incidence of dizziness and ataxia 2
• Amantadine resistance can develop during treatment, so therapy should be limited to 3-5 days when possible 2, 5

Important Caveats

• Amantadine is not a substitute for influenza vaccination 1
• In Parkinson's disease, amantadine is less effective than levodopa 1
• Patients may experience decreased effectiveness after a few months of use for Parkinson's disease; temporary discontinuation followed by reinitiation may restore benefit 1
• Due to high levels of adamantane resistance among current influenza A strains, neuraminidase inhibitors (oseltamivir, zanamivir) may be preferred for influenza treatment in many regions 5
• Amantadine has a large volume of distribution and can accumulate in patients with impaired renal function, potentially leading to toxicity 4