Amantadine: Effective Symptom Control in Parkinsonism and Influenza A
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Synonyms | |||
Amantadine is a versatile antiviral and antiparkinsonian agent with a well-established clinical profile. Originally developed for influenza prophylaxis, its utility in managing Parkinson’s disease symptoms, particularly drug-induced extrapyramidal symptoms, has made it a valuable therapeutic option. This medication functions through multiple mechanisms including NMDA receptor antagonism and dopamine facilitation, providing unique benefits for neurological and infectious indications.
Features
- Chemical classification: Adamantane derivative
- Available formulations: 100 mg capsules and oral syrup (50 mg/5 mL)
- Mechanism: NMDA receptor antagonism and dopamine augmentation
- Half-life: Approximately 12-18 hours in adults with normal renal function
- Administration: Oral route with excellent bioavailability
Benefits
- Reduces parkinsonian tremor, rigidity, and bradykinesia through dopaminergic and antiglutamatergic actions
- Provides effective prophylaxis against influenza A virus strains when administered appropriately
- Demonstrates efficacy in managing levodopa-induced dyskinesias without worsening parkinsonism
- May improve fatigue and cognitive symptoms in multiple sclerosis patients
- Offers flexible dosing options suitable for geriatric populations
- Shows rapid onset of action for parkinsonian symptoms, often within 48 hours
Common use
Amantadine is primarily indicated for the treatment of Parkinson’s disease symptoms, particularly in early-stage disease or as adjunctive therapy with levodopa. It’s also approved for prophylaxis and treatment of respiratory tract infections caused by influenza A virus strains. Off-label uses include management of drug-induced extrapyramidal symptoms, fatigue in multiple sclerosis, and cognitive enhancement in traumatic brain injury. The medication has shown particular utility in managing levodopa-induced dyskinesias while maintaining antiparkinsonian effects.
Dosage and direction
For Parkinson’s disease: Initiate at 100 mg once daily, increasing to 100 mg twice daily after one week if necessary. Maximum dose: 400 mg daily in divided doses. For influenza prophylaxis: 200 mg once daily or 100 mg twice daily. For influenza treatment: 200 mg initially, then 100 mg daily or 100 mg twice daily. Renal impairment requires dosage adjustment: 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.
Precautions
Monitor renal function regularly during therapy. Use caution in patients with history of seizures, as amantadine may lower seizure threshold. Elderly patients are more susceptible to CNS side effects and require careful titration. Patients with congestive heart failure or peripheral edema require cardiovascular monitoring. Psychiatric symptoms including depression, anxiety, and hallucinations may occur, particularly in elderly patients. Abrupt discontinuation may cause neuroleptic malignant syndrome or parkinsonian crisis.
Contraindications
Hypersensitivity to amantadine or any component of the formulation. Severe renal impairment (CrCl <15 mL/min) without appropriate dosage adjustment. History of angle-closure glaucoma. Concurrent use of live attenuated influenza vaccine. Pregnancy unless potential benefit justifies potential risk to fetus. Breastfeeding is not recommended due to secretion in human milk.
Possible side effect
Common reactions include nausea (5-10%), dizziness (5-7%), insomnia (5-10%), and peripheral edema (5-15%). Less frequently, patients may experience livedo reticularis (1-5%), orthostatic hypotension (2-5%), and anticholinergic effects. Neuropsychiatric effects including confusion, hallucinations, and anxiety occur in approximately 5-10% of patients, particularly in elderly populations. Rare but serious side effects include neuroleptic malignant syndrome upon withdrawal, suicidal ideation, and cardiomyopathy.
Drug interaction
Significant interactions occur with anticholinergic agents (additive CNS effects), CNS stimulants (increased nervousness and insomnia), and drugs affecting renal excretion. Triamterene and hydrochlorothiazide reduce amantadine clearance by 20-30%. Alcohol may enhance CNS depression. Co-administration with memantine should be avoided due to similar mechanisms. QT-prolonging agents may have additive effects on cardiac repolarization.
Missed dose
If a dose is missed, take it as soon as remembered unless it’s nearly time for the next dose. Do not double doses. For twice-daily regimens, if missed for more than 4 hours, skip and resume regular schedule. Maintain consistent timing to ensure stable plasma concentrations. If multiple doses are missed, contact healthcare provider for guidance on re-initiation.
Overdose
Symptoms include severe nausea, vomiting, blurred vision, hallucinations, seizures, and cardiac arrhythmias. Management involves gastric lavage if presented early, activated charcoal, and supportive care. Acidification of urine may enhance elimination. Hemodialysis may be effective due to amantadine’s relatively low molecular weight and partial protein binding. Cardiac monitoring is essential for 24-48 hours post-ingestion.
Storage
Store at controlled room temperature (20-25°C/68-77°F). Protect from light and moisture. Keep container tightly closed. Do not freeze oral solution. Discard any unused portion after 30 days of opening. 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. Always consult with a qualified healthcare professional before starting or changing any medication regimen. Individual response to amantadine may vary based on clinical status, renal function, and concomitant medications. Proper diagnosis and monitoring are essential for safe and effective use.
Reviews
Clinical studies demonstrate amantadine’s efficacy in reducing Unified Parkinson’s Disease Rating Scale scores by 20-30% in moderate disease. For influenza prophylaxis, meta-analyses show 61-91% effectiveness against susceptible strains. Patient-reported outcomes indicate significant improvement in quality of life measures, particularly regarding reduction of dyskinesias and improvement in mobility. Long-term studies show maintained efficacy for up to 2 years in Parkinson’s disease management with appropriate monitoring.