Amantadine is a versatile antiviral and neurological agent with a well-established clinical profile, primarily indicated for the prophylaxis and treatment of influenza A virus infections and the management of Parkinson’s disease symptoms. It functions through dual mechanisms: as an antiviral by inhibiting viral uncoating and replication, and in neurology by modulating dopaminergic neurotransmission and exhibiting NMDA receptor antagonist properties. Its utility spans both acute infectious scenarios and chronic neurodegenerative care, supported by decades of clinical use and evidence.

Features

• Chemical name: 1-adamantanamine hydrochloride
• Molecular formula: C₁₀H₁₇N·HCl
• Mechanism: Blocks viral M2 ion channel; enhances dopamine release, inhibits reuptake
• Administration: Oral tablet or capsule; syrup formulation available
• Bioavailability: Approximately 90% following oral administration
• Half-life: 12–18 hours in adults with normal renal function
• Excretion: Primarily renal (≥90% unchanged)

Benefits

• Reduces duration and severity of influenza A symptoms when administered early
• Provides symptomatic relief in Parkinson’s disease, including reduction of rigidity and bradykinesia
• May ameliorate drug-induced extrapyramidal symptoms in psychiatric settings
• Demonstrates neuroprotective potential via NMDA receptor antagonism
• Offers a well-tolerated option with a predictable pharmacokinetic profile
• Available in generic formulations, enhancing accessibility and cost-effectiveness

Common use

Amantadine is commonly prescribed for two primary indications: the prophylaxis and treatment of influenza A virus and the management of Parkinson’s disease. In virology, it is used particularly during outbreaks or for high-risk populations, such as the elderly or immunocompromised individuals, to prevent infection or reduce symptom duration. In neurology, it is employed as monotherapy in early Parkinson’s disease or as an adjunct to levodopa to manage motor fluctuations and dyskinesias. Off-label uses include addressing fatigue in multiple sclerosis and managing extrapyramidal side effects induced by antipsychotic medications.

Dosage and direction

For influenza A prophylaxis in adults: 200 mg once daily or 100 mg twice daily. For treatment: 200 mg initially, then 100 mg daily or 100 mg twice daily, beginning within 24–48 hours of symptom onset. Duration typically ranges from 24–48 hours after symptom resolution up to 10 days.
For Parkinson’s disease: Initial dose of 100 mg daily, increased to 100 mg twice daily after one week if tolerated. Maximum dose is 400 mg daily in divided doses, though lower doses are often effective.
Dosage must be adjusted in renal impairment: For CrCl 30–50 mL/min, 200 mg on first day, then 100 mg daily; for CrCl 15–29 mL/min, 200 mg on first day, then 100 mg on alternate days; for CrCl <15 mL/min, 200 mg every 7 days. Administer with or without food; evening doses should be taken several hours before bedtime to minimize insomnia.

Precautions

Use with caution in patients with a history of seizures, as amantadine may lower seizure threshold. Monitor for signs of congestive heart failure or peripheral edema, particularly in those with cardiovascular compromise. Psychiatric symptoms, including hallucinations, agitation, or depression, may occur and require evaluation. Avoid abrupt discontinuation in Parkinson’s patients to prevent acute symptom exacerbation. Renal function should be assessed before and during therapy, with appropriate dose adjustments. Elderly patients are more susceptible to CNS and adverse effects; initiate at lower doses. Not recommended during pregnancy unless potential benefit justifies risk (Category C). Exercise caution in patients with eczema or recurrent rash due to potential for dermatological reactions.

Contraindications

Hypersensitivity to amantadine or any component of the formulation. Severe renal impairment (CrCl <15 mL/min) without appropriate dose adjustment. Concurrent use of live attenuated influenza vaccine, as antiviral activity may reduce vaccine efficacy.

Possible side effect

Common: nausea, dizziness, insomnia, dry mouth, peripheral edema.
Less common: orthostatic hypotension, livedo reticularis, anxiety, confusion, visual disturbances.
Rare: leukopenia, neutropenia, heart failure, neuroleptic malignant syndrome (upon withdrawal), suicidal ideation.
Most side effects are dose-dependent and reversible upon discontinuation or dose reduction.

Drug interaction

Increased anticholinergic effects with other anticholinergic agents (e.g., trihexyphenidyl). Enhanced CNS stimulation with sympathomimetics or stimulants. Concurrent use with alcohol may increase CNS depression. Co-administration with thiazide diuretics may reduce amantadine clearance. QT-prolonging agents may have additive effects. Avoid with memantine due to similar mechanism and increased adverse effect risk.

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 catch up. Resume the regular dosing schedule. For once-daily regimens, if missed entirely, take the next dose at the usual time the following day.

Overdose

Symptoms may include agitation, hallucinations, cardiac arrhythmias, hyperthermia, and respiratory distress. Management is supportive: ensure airway protection, administer activated charcoal if presented early, and consider IV fluids for hydration. Hemodialysis may be effective due to the drug’s renal excretion. Monitor ECG and electrolytes; benzodiazepines may be used for agitation or seizures. Contact poison control for specific guidance.

Storage

Store at controlled room temperature (20–25°C). Protect from light and moisture. Keep in the original container, tightly closed. Do not freeze liquid formulations. Keep out of reach of children and pets. Discard any unused medication after the expiration date or course completion, following local disposal guidelines.

Disclaimer

This information is for educational purposes and does not replace professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before starting, changing, or stopping any medication. Individual response to amantadine may vary based on health status, comorbidities, and concomitant therapies. The prescriber is responsible for determining appropriate use and monitoring.

Reviews

Clinical studies and meta-analyses support amantadine’s efficacy in reducing influenza A symptom duration by approximately 1–2 days when initiated early. In Parkinson’s disease, it demonstrates meaningful improvement in Unified Parkinson’s Disease Rating Scale (UPDRS) scores and reduced dyskinesia severity. Long-term use is associated with tolerable side effects, though some patients develop tolerance to anti-parkinsonian effects over time. Overall, it remains a valuable option in specific clinical contexts, with a favorable risk-benefit profile when used appropriately.