Amantadine is a synthetic tricyclic amine with antiviral and antiparkinsonian properties. In India, it is primarily used for the treatment of Parkinson's disease and drug-induced extrapyramidal symptoms. It acts as a weak, non-competitive NMDA receptor antagonist and facilitates dopaminergic neurotransmission. It is also approved for prophylaxis and treatment of influenza A virus infections, though this use has declined with newer antivirals.
Adult: Parkinson's/Extrapyramidal: 100 mg once or twice daily. Start with 100 mg once daily, may increase to 100 mg twice daily after 1 week if needed. Influenza Prophylaxis: 100 mg once daily. Influenza Treatment: 100 mg twice daily for 3-5 days or 24-48 hours after symptoms disappear.
Note: Can be taken with or without food. If gastrointestinal upset occurs, take with food. Swallow the tablet whole with a glass of water. For Parkinson's, if dose is >100 mg/day, split into two doses (morning and noon) to avoid insomnia. Do not take dose late in the evening.
Amantadine's antiparkinsonian effect is multifactorial: 1) It increases dopamine release from presynaptic terminals and may inhibit its reuptake. 2) It exhibits anticholinergic activity. 3) It is a weak, non-competitive antagonist of NMDA (N-methyl-D-aspartate) glutamate receptors, which may reduce excitotoxicity and improve motor function. Its antiviral action against influenza A is via inhibition of the viral M2 protein ion channel, preventing viral uncoating and replication within the host cell.
Pregnancy: Category C (US FDA). Animal studies have shown teratogenicity. Use only if potential benefit justifies potential risk to the fetus. Not recommended for routine use in pregnancy, especially for influenza.
Driving: May impair mental and/or physical abilities required for driving or operating machinery. Patients should be cautioned, especially at initiation of therapy or dose increase.
| Trihexyphenidyl, Benztropine | Additive anticholinergic side effects (confusion, dry mouth, constipation, urinary retention). | Major |
| Levodopa/Carbidopa | Additive therapeutic benefit but also increased risk of hallucinations, confusion, and orthostatic hypotension. | Moderate |
| Memantine | Both are NMDA antagonists; increased risk of CNS toxicity (dizziness, confusion). | Major |
| Quinidine, Trimethoprim | Reduce renal tubular secretion of amantadine, increasing its plasma levels and toxicity risk. | Major |
| Central Nervous System Depressants (Alcohol, Benzodiazepines, Opioids) | Increased sedative effects and risk of dizziness/falls. | Moderate |
| Antipsychotics (e.g., Haloperidol, Chlorpromazine) | May diminish antiparkinsonian effect and worsen extrapyramidal symptoms. | Moderate |
| Anticholinergic drugs (e.g., Amitriptyline, Oxybutynin) | Increased anticholinergic burden. | Moderate |