Amantadine: Effective Antiviral and Parkinson's Symptom Management
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Synonyms | |||
Amantadine is a synthetic antiviral and antiparkinsonian agent with a well-established clinical profile. Originally developed as an antiviral medication, its therapeutic applications have expanded to include the management of Parkinson’s disease and drug-induced extrapyramidal symptoms. This medication functions through multiple mechanisms of action, including inhibition of viral uncoating and modulation of dopaminergic neurotransmission. Its dual indications make it a valuable option in neurologic and infectious disease therapeutics, supported by decades of clinical evidence and prescribing experience.
Features
- Chemical name: 1-adamantanamine hydrochloride
- Molecular formula: C₁₀H₁₇N·HCl
- Molecular weight: 187.71 g/mol
- Appearance: White crystalline powder
- Solubility: Freely soluble in water and alcohol
- Available formulations: 100 mg capsules, 50 mg/5 mL syrup, 100 mg tablets
- Mechanism: Blocks viral M2 ion channel; enhances dopamine release and inhibits reuptake
- Half-life: Approximately 12-18 hours in adults
- Protein binding: ~67%
- Metabolism: Minimal hepatic metabolism
- Excretion: Primarily renal (90% unchanged)
Benefits
- Provides effective prophylaxis against influenza A virus infections when administered appropriately
- Reduces parkinsonian symptoms including rigidity, bradykinesia, and tremor
- Manages drug-induced extrapyramidal symptoms caused by antipsychotic medications
- Demonstrates relatively rapid onset of action in Parkinson’s disease management
- Offers convenient once or twice daily dosing regimen for most indications
- Presents generally favorable tolerability profile when appropriately dosed
Common use
Amantadine is primarily indicated for the prophylaxis and treatment of respiratory tract infections caused by influenza A virus strains. In neurologic practice, it is widely used as monotherapy or adjunctive treatment for Parkinson’s disease, particularly for patients experiencing diminished response to levodopa or those requiring symptomatic relief between doses. Additionally, it is employed off-label for managing fatigue in multiple sclerosis and various movement disorders. The medication has shown utility in addressing levodopa-induced dyskinesias while maintaining antiparkinsonian benefits.
Dosage and direction
For influenza prophylaxis in adults: 200 mg once daily or 100 mg twice daily. For treatment of influenza infection: 200 mg initially, followed by 100 mg once or twice daily. For Parkinson’s disease: Initial dose of 100 mg once daily, increasing to 100 mg twice daily after one week if necessary. Maximum recommended dose is 400 mg daily in divided doses. For patients with renal impairment (creatinine clearance 30-50 mL/min): 200 mg first day, then 100 mg daily. For severe renal impairment (creatinine clearance 15-29 mL/min): 200 mg first day, then 100 mg every other day. Administration with food may minimize gastrointestinal discomfort. Dosage adjustments are necessary in elderly patients and those with impaired renal function.
Precautions
Patients should be monitored for signs of congestive heart failure, peripheral edema, and orthostatic hypotension. Neuropsychiatric symptoms including depression, anxiety, and hallucinations require careful assessment. Caution is advised in patients with history of seizures, as amantadine may lower seizure threshold. Renal function should be evaluated before initiation and periodically during treatment. Patients should avoid abrupt discontinuation to prevent rebound parkinsonism or neuroleptic malignant syndrome. Those with livedo reticularis should be monitored for dermatologic changes. Driving and operating machinery may be impaired due to potential dizziness or blurred vision.
Contraindications
Hypersensitivity to amantadine or any component of the formulation. Severe renal impairment (creatinine clearance <15 mL/min) without appropriate dosage adjustment. History of angle-closure glaucoma. Concurrent use of memantine due to similar pharmacological properties and increased risk of adverse effects. Pregnancy unless potential benefits outweigh risks (Category C). Breastfeeding is not recommended due to secretion into human milk. Patients with uncontrolled hypertension or severe cardiovascular disease require careful risk-benefit assessment.
Possible side effect
Common adverse effects (>10%) include nausea, dizziness, lightheadedness, and insomnia. Less frequent effects (1-10%) comprise dry mouth, constipation, peripheral edema, livedo reticularis, and orthostatic hypotension. Neuropsychiatric effects including anxiety, irritability, and confusion may occur, particularly in elderly patients. Rare but serious adverse reactions (<1%) include suicidal ideation, psychosis, seizures, leukopenia, and neuroleptic malignant syndrome upon abrupt withdrawal. Cardiovascular effects such as congestive heart failure and arrhythmias have been reported in susceptible individuals.
Drug interaction
Increased anticholinergic effects when combined with other anticholinergic medications. Enhanced central nervous system stimulation with sympathomimetic agents. Reduced clearance when administered with quinine or quinidine. Potential for increased toxicity with other renally eliminated drugs. Alcohol may enhance CNS effects and impair alertness. Co-administration with thioridazine may increase risk of Parkinsonian symptoms. Triamterene-hydrochlorothiazide may reduce amantadine clearance. Carbidopa-levodopa combinations may enhance therapeutic effects but also increase dyskinesia risk.
Missed dose
If a dose is missed, it should be taken as soon as remembered unless it is nearly time for the next scheduled dose. In that case, the missed dose should be skipped and the regular dosing schedule resumed. Patients should not double the dose to make up for a missed administration. Consistent timing is important for maintaining stable plasma concentrations, particularly for antiviral prophylaxis. Healthcare providers should be consulted if multiple doses are missed or if uncertainty exists regarding proper dosing resumption.
Overdose
Amantadine overdose may manifest as agitation, hallucinations, psychotic behavior, cardiac arrhythmias, hypertension or hypotension, hyperthermia, respiratory distress, and convulsions. Management includes gastric lavage if presented early, activated charcoal administration, and supportive care with monitoring of vital signs. Acidification of urine may enhance elimination, though this approach requires careful consideration of acid-base status. Hemodialysis may be effective in removing amantadine from circulation. Benzodiazepines may be used for agitation or seizures, while antiarrhythmics may be necessary for cardiac complications.
Storage
Store at controlled room temperature (20-25°C or 68-77°F). Protect from light and moisture. Keep container tightly closed. Do not freeze liquid formulations. Keep out of reach of children and pets. Do not use beyond the expiration date printed on packaging. Properly discard any unused medication through take-back programs or according to local regulations. Do not flush medications down the toilet or pour into drains unless specifically instructed to do so.
Disclaimer
This information is provided for educational purposes only and does not constitute medical advice. Healthcare professionals should exercise clinical judgment when prescribing amantadine, considering individual patient factors and current treatment guidelines. Patients should consult their healthcare provider before starting or changing any medication regimen. The prescribing information included here may not be comprehensive, and practitioners should refer to the complete prescribing information and latest clinical guidelines. Off-label uses should be carefully considered with appropriate informed consent.
Reviews
Clinical studies demonstrate amantadine’s efficacy in influenza prophylaxis with approximately 70-90% effectiveness against susceptible strains. In Parkinson’s disease, multiple trials show significant improvement in Unified Parkinson’s Disease Rating Scale scores, with particular benefit for bradykinesia and rigidity. Systematic reviews indicate moderate evidence for reducing levodopa-induced dyskinesias. Patient-reported outcomes generally reflect improved mobility and quality of life, though individual responses vary. Long-term experience supports its safety profile when appropriately monitored, though tolerance may develop in some Parkinson’s patients requiring dosage adjustments.