Comprehensive Guide to Amantadine: Uses, Dosage, Side Effects, and More
What is Amantadine?
Overview of Amantadine
Generic Name: Amantadine
Brand Name: Symmetrel, Gocovri (extended-release), Osmolex ER (extended-release), generics
Drug Group: Antiviral; antiparkinsonian; dopaminergic agent
The medication is used to:
- Prevent and treat influenza A infections (not effective against influenza B).
- Manage symptoms of Parkinson’s disease (e.g., tremor, rigidity).
- Treat extrapyramidal symptoms caused by antipsychotics or other drugs.
- Off-label uses include managing levodopa-induced dyskinesia in Parkinson’s disease or fatigue in multiple sclerosis under specialist guidance.
Key Characteristics
Form: Oral capsules (100 mg), tablets (100 mg), syrup (50 mg/5 mL), extended-release capsules (Gocovri: 68.5 mg, 137 mg), extended-release tablets (Osmolex ER: 129 mg, 193 mg, 258 mg).
Mechanism: Inhibits influenza A M2 ion channel to prevent viral uncoating; enhances dopamine release and blocks NMDA receptors for neurological effects.
Approval: FDA-approved (1966 for Symmetrel) and EMA-approved for influenza and Parkinson’s disease.
Indications and Uses of Amantadine
Influenza A: Prophylaxis and treatment in adults and children ≥1 year, though limited by widespread viral resistance.
Parkinson’s Disease: Improves motor symptoms (e.g., tremor, bradykinesia) in adults, often as adjunct therapy.
Drug-Induced Extrapyramidal Symptoms: Reduces movement disorders (e.g., dystonia, akathisia) caused by antipsychotics.
Off-Label Uses: Manages levodopa-induced dyskinesia, fatigue in multiple sclerosis, or traumatic brain injury symptoms under specialist supervision.
Dosage of Amantadine
Dosage for Adults
Influenza A (Prophylaxis/Treatment):
- 200 mg daily (as a single dose or 100 mg twice daily).
- Duration: Treatment for 5–7 days; prophylaxis during exposure risk (e.g., 10–14 days).
Parkinson’s Disease (Immediate-Release):
- Initial: 100 mg daily.
- Maintenance: 100–400 mg daily in divided doses (maximum 400 mg/day).
Drug-Induced Extrapyramidal Symptoms: 100 mg twice daily; may increase to 300 mg/day if needed.
Parkinson’s Dyskinesia (Gocovri):
- Initial: 137 mg once daily at bedtime.
- Maintenance: 274 mg once daily (maximum).
Parkinson’s Symptoms (Osmolex ER):
- Initial: 129 mg once daily in the morning.
- Maintenance: 129–322 mg/day (maximum 322 mg/day).
Dosage for Children
Influenza A:
- 1–9 years: 4.4–8.8 mg/kg/day (maximum 150 mg/day).
- ≥10 years (≥40 kg): 200 mg daily (single dose or 100 mg twice daily).
Dosage for Pregnant Women
Dosage Adjustments
Renal Impairment:
- CrCl 30–50 mL/min: 100 mg daily or every other day.
- CrCl 15–29 mL/min: 100 mg every 2–3 days.
- CrCl <15 mL/min or dialysis: Not recommended.
Hepatic Impairment: No specific adjustments; monitor for side effects.
Elderly: Start with 100 mg daily; monitor for confusion, falls, or hallucinations.
Additional Considerations
- Take immediate-release forms with or without food; extended-release forms (Gocovri, Osmolex ER) have specific timing (bedtime or morning).
- Syrup requires accurate measurement with a dosing device.
How to Use Amantadine
Administration:
- Capsules/Tablets: Swallow whole with water, with or without food.
- Syrup: Measure with a dosing device; shake well before use.
- Extended-Release (Gocovri): Take at bedtime; swallow whole, do not crush or chew.
- Extended-Release (Osmolex ER): Take in the morning; swallow whole.
Timing: Follow prescribed schedule (daily or twice daily for immediate-release; once daily for extended-release).
Missed Dose: Take as soon as remembered unless it’s nearly time for the next dose; do not double doses. Consult your doctor if multiple doses are missed.
Additional Tips:
- Avoid alcohol, as it may increase dizziness or confusion.
- Report symptoms like hallucinations, confusion, or swelling promptly.
Contraindications for Amantadine
Patients with hypersensitivity to Amantadine or its components.
Patients with end-stage renal disease (CrCl <15 mL/min) or on dialysis.
Warnings & Precautions for Amantadine
General Warnings
Central Nervous System Effects: Risk of dizziness, confusion, hallucinations, or seizures; monitor closely, especially in elderly patients.
Neuroleptic Malignant Syndrome (NMS): Rare; may occur with dose reduction or discontinuation in Parkinson’s patients; watch for fever, rigidity, or altered mental status.
Orthostatic Hypotension: Risk of low blood pressure or fainting; rise slowly from sitting or lying positions.
Suicidal Ideation: Rare; monitor for mood changes or depression.
Heart Failure: May worsen in patients with congestive heart failure; monitor for edema or weight gain.
Use in Specific Populations
Pregnancy: Category C; limited data; use cautiously with specialist consultation.
Breastfeeding: Excreted in breast milk; avoid or use cautiously after weighing risks.
Elderly: Increased risk of confusion, hallucinations, or falls; use lower doses.
Children: Approved for influenza A (≥1 year); not established for neurological uses.
Renal Impairment: Contraindicated in severe cases; adjust dose in mild to moderate impairment.
Additional Precautions
- Inform your doctor about kidney disease, seizure history, or psychiatric conditions before starting the medication.
- Avoid abrupt discontinuation in Parkinson’s patients to prevent symptom worsening or NMS.
Overdose and Management of Amantadine
Overdose Symptoms
- Severe confusion, hallucinations, or agitation.
- Seizures or arrhythmias.
- Hypotension or respiratory depression.
Immediate Actions
Contact Emergency Services: Call 911 or seek medical help immediately.
Supportive Care: Monitor vital signs, manage seizures (e.g., with benzodiazepines), and provide cardiovascular support.
Monitor: Check renal function and electrolytes; hemodialysis is ineffective due to large volume of distribution.
Additional Notes
- Overdose is rare with proper dosing; store securely to prevent misuse.
- Report persistent symptoms promptly.
Side Effects of Amantadine
Common Side Effects
- Dizziness (5–10%)
- Nausea (3–5%)
- Insomnia (2–4%)
- Dry mouth (1–3%)
- Constipation (1–3%)
These effects are often mild and may resolve with continued use.
Serious Side Effects
Neurological: Hallucinations, confusion, or seizures.
Cardiovascular: Irregular heartbeat or fainting (orthostatic hypotension).
Psychiatric: Depression, suicidal thoughts, or agitation.
Allergic Reactions: Rare; rash, swelling, or difficulty breathing.
Additional Notes
- Regular monitoring for neurological or psychiatric symptoms is essential, especially in elderly patients.
- Report persistent or severe side effects promptly.
Drug Interactions with Amantadine
The medication may interact with:
Anticholinergics (e.g., Benztropine): Increase risk of confusion or hallucinations; monitor closely.
CNS Stimulants (e.g., Methylphenidate): Enhance CNS side effects; use cautiously.
Alcohol: Increases dizziness or confusion; avoid during treatment.
Live Influenza Vaccines: Amantadine may reduce vaccine efficacy; separate by 48 hours before and 2 weeks after vaccination.
Quinidine/Quinine: May increase Amantadine levels; monitor for toxicity.
Patient Education or Lifestyle
Medication Adherence: Take Amantadine as prescribed to ensure efficacy. Refill prescriptions early to avoid interruptions.
Monitoring: Report symptoms like confusion, hallucinations, or swelling immediately. Regular follow-ups are needed for neurological conditions.
Lifestyle: For Parkinson’s, engage in physical therapy or exercise to support mobility; for influenza, practice good hygiene to prevent spread.
Diet: Stay hydrated and maintain a balanced diet; avoid alcohol to reduce CNS side effects.
Emergency Awareness: Carry information about your condition (e.g., Parkinson’s) and medications; know signs of seizures or NMS.
Vaccination: Get annual influenza vaccination, but coordinate timing with Amantadine use for prophylaxis.
Pharmacokinetics of Amantadine
Absorption: Well-absorbed orally; peak plasma concentration at 1–4 hours.
Distribution: Volume of distribution ~3–8 L/kg; crosses blood-brain barrier.
Metabolism: Minimal; not significantly metabolized.
Excretion: Primarily renal (>90% unchanged); clearance dependent on kidney function.
Half-Life: 10–31 hours (average 16 hours); prolonged in renal impairment.
Pharmacodynamics of Amantadine
The antiviral exerts its effects by:
Inhibiting influenza A M2 ion channel, preventing viral uncoating and replication.
Enhancing dopamine release and blocking NMDA receptors, improving motor symptoms in Parkinson’s and extrapyramidal disorders.
Reducing dyskinesia in Parkinson’s (extended-release forms) by modulating glutamate activity.
Providing symptom relief within days for neurological conditions, though antiviral efficacy is limited by resistance.
Storage of Amantadine
Temperature: Store at room temperature (20–25°C or 68–77°F); avoid moisture and heat.
Protection: Keep capsules/tablets in original container; store syrup tightly closed.
Safety: Store out of reach of children to prevent accidental ingestion.
Disposal: Follow local regulations or consult a pharmacist for safe disposal of unused or expired medication.
Frequently Asked Questions (FAQs)
Q: What does Amantadine treat?
A: The drug treats influenza A, Parkinson’s disease, and drug-induced movement disorders.
Q: Can Amantadine cause confusion?
A: Yes, especially in the elderly; report confusion or hallucinations immediately.
Q: Is Amantadine safe for children?
A: Approved for influenza A in children ≥1 year; not for neurological uses.
Q: How long does Amantadine take to work?
A: Antiviral effects begin within 48 hours; neurological benefits may take days to weeks.
Q: Can I stop Amantadine suddenly?
A: No, taper gradually in Parkinson’s to avoid symptom worsening or neuroleptic malignant syndrome.
Regulatory Information
The medication is approved by:
U.S. Food and Drug Administration (FDA): Approved in 1966 (Symmetrel) for influenza and Parkinson’s; later for Gocovri and Osmolex ER.
European Medicines Agency (EMA): Approved for influenza and Parkinson’s disease.
Other Agencies: Approved globally for equivalent uses; consult local guidelines.
References
- U.S. Food and Drug Administration (FDA). (2023). Symmetrel (Amantadine) Prescribing Information.
- Official FDA documentation detailing the drug’s approved uses, dosage, and safety.
- European Medicines Agency (EMA). (2023). Amantadine Summary of Product Characteristics.
- EMA’s comprehensive information on the medication’s indications and precautions in Europe.
- National Institutes of Health (NIH). (2023). Amantadine: MedlinePlus Drug Information.
- NIH resource providing detailed information on the drug’s uses, side effects, and precautions.
- World Health Organization (WHO). (2023). WHO Model List of Essential Medicines: Amantadine.
- WHO’s inclusion of Amantadine for Parkinson’s and influenza.
- Neurology. (2020). Amantadine in Parkinson’s Disease and Dyskinesia.
- Peer-reviewed article on Amantadine efficacy (note: access may require a subscription).
