Amantadine for Effective Parkinson's and Influenza Management
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Synonyms | |||
Amantadine is a versatile antiviral and antiparkinsonian agent with a well-established clinical profile. Originally developed as an antiviral for influenza A, its dopaminergic and antiglutamatergic properties have made it a valuable therapeutic option in neurology. This medication offers a dual mechanism of action, providing both symptomatic relief in Parkinson’s disease and prophylaxis/treatment for certain viral infections, supported by decades of clinical evidence and a favorable safety profile when used appropriately under medical supervision.
Features
- Chemical name: 1-adamantanamine hydrochloride
- Molecular formula: C₁₀H₁₇N·HCl
- Mechanism: Dopamine facilitation, NMDA receptor antagonism, viral uncoating inhibition
- Bioavailability: Approximately 90% orally
- Half-life: 12–18 hours (prolonged in renal impairment)
- Excretion: Primarily renal (unchanged)
- Formulations: 100 mg capsules, 50 mg/5 mL syrup
Benefits
- Reduces parkinsonian rigidity, bradykinesia, and tremor through dopaminergic enhancement
- Decreases levodopa-induced dyskinesias via NMDA receptor antagonism
- Provides prophylaxis and early treatment against influenza A virus strains
- May improve fatigue and cognitive symptoms in multiple sclerosis and traumatic brain injury
- Allows for flexible dosing adjustments based on renal function and clinical response
- Well-tolerated in most patients with appropriate monitoring and contraindication screening
Common use
Amantadine is primarily indicated for the treatment of Parkinson’s disease, particularly for managing early-stage symptoms and reducing dyskinesias associated with long-term levodopa therapy. It is also approved for the prophylaxis and symptomatic treatment of respiratory tract infections caused by influenza A virus strains. Off-label uses include fatigue management in multiple sclerosis, enhancement of cognitive recovery following traumatic brain injury, and treatment of certain neuroleptic-induced extrapyramidal symptoms. Clinical decision-making should always involve strain-specific antiviral susceptibility testing when used for influenza and careful neurological assessment for movement disorders.
Dosage and direction
For Parkinson’s disease: Initiate at 100 mg once daily, increasing to 100 mg twice daily after one week if tolerated. Maximum dose: 400 mg daily in divided doses, though most patients respond to 100–200 mg daily. For influenza prophylaxis: 200 mg once daily or 100 mg twice daily. For influenza treatment: 200 mg once daily or 100 mg twice daily initiated within 24–48 hours of symptom onset. Renal dosing adjustment mandatory: CrCl 30–50 mL/min: 200 mg first day, then 100 mg daily; CrCl 15–29 mL/min: 200 mg first day, then 100 mg every other day; CrCl <15 mL/min: 200 mg every 7 days. Administer with or without food; evening doses should be given before 6 PM to reduce insomnia risk.
Precautions
Monitor renal function at baseline and periodically during treatment. Use caution in patients with history of seizures, psychiatric disorders, or cardiovascular disease. May cause orthostatic hypotension; advise slow position changes. CNS effects including dizziness and confusion are more common in elderly patients. Avoid abrupt discontinuation (risk of neuroleptic malignant syndrome-like reaction or parkinsonian crisis). Use protective measures against sun exposure due to photosensitivity risk. Not recommended during pregnancy unless potential benefit justifies potential risk (Category C). Breastfeeding should be avoided due to secretion into human milk.
Contraindications
Hypersensitivity to amantadine or any component of the formulation. Severe renal impairment (CrCl <15 mL/min) without appropriate dosing adjustment. Concurrent use of live attenuated influenza vaccine within 48 hours of amantadine administration. Untreated narrow-angle glaucoma. History of recurrent eczema or uncontrolled psoriasis. Concomitant use with other NMDA antagonists (e.g., memantine, ketamine) due to additive neuropsychiatric effects.
Possible side effect
Common (≥5%): nausea, dizziness, insomnia, anxiety, peripheral edema, livedo reticularis. Less common (1–5%): constipation, dry mouth, orthostatic hypotension, visual disturbances, headache. Rare (<1%): hallucinations, confusion, suicidal ideation, seizures, leukopenia, heart failure exacerbation. Most side effects are dose-dependent and reversible upon dosage reduction or discontinuation. Livedo reticularis (mottled skin appearance) typically appears after months of therapy and is generally benign.
Drug interaction
Anticholinergic agents: increased risk of confusion, hallucinations, and dry mouth. CNS depressants (alcohol, benzodiazepines, opioids): additive sedation and dizziness. Dopaminergic agents: enhanced therapeutic and adverse effects. Thiazide diuretics: may reduce amantadine clearance. Drugs affecting renal secretion (cimetidine, quinidine, trimethoprim): may increase amantadine levels. Memantine: contraindicated due to pharmacodynamic overlap. Metoclopramide: may antagonize antiparkinsonian effects.
Missed dose
If a dose is missed, take it as soon as remembered unless it is nearly time for the next dose. Do not double the dose to make up for a missed administration. For twice-daily regimens, if missed for more than 4 hours, skip and resume normal schedule. Consistent timing is important for maintaining stable plasma concentrations, particularly for antiparkinsonian effects.
Overdose
Symptoms may include severe nausea/vomiting, agitation, hallucinations, cardiac arrhythmias, hyperthermia, respiratory depression, and seizures. Serum levels >1.0 μg/mL are considered toxic. Management includes gastric lavage if presented early, activated charcoal, IV fluids, and symptomatic support. Acidification of urine may enhance elimination but is controversial due to risk of crystal formation. Hemodialysis may be effective (20–60% removal). Cardiac monitoring is essential for 48 hours due to risk of QT prolongation.
Storage
Store at controlled room temperature (20–25°C/68–77°F). Protect from light and moisture. Keep bottle tightly closed. Do not freeze the oral solution. Discard any unused portion after 90 days of opening the bottle. Keep out of reach of children and pets. Do not transfer capsules to other containers without proper labeling.
Disclaimer
This information is for educational purposes only and does not constitute medical advice. Prescription and use of amantadine must be under the supervision of a qualified healthcare professional. Dosage and indications may vary based on individual patient factors, regional guidelines, and emerging evidence. Always consult the most current prescribing information and clinical guidelines before administration.
Reviews
Clinical studies demonstrate approximately 60–70% efficacy in reducing parkinsonian symptoms and 40–50% reduction in levodopa-induced dyskinesias. For influenza prophylaxis, efficacy ranges from 50–90% depending on strain susceptibility. Systematic reviews note generally favorable tolerability compared to other antiparkinsonian agents, though CNS side effects remain a limitation in vulnerable populations. Long-term registry data support maintained efficacy for up to 2–3 years in Parkinson’s disease, after which benefit may diminish due to receptor changes. Patient-reported outcomes indicate particular satisfaction with dyskinesia reduction and improved mobility.