Amantadine Dosage Calculator
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Amantadine is a synthetic adamantane derivative used as an antiviral and in the management of Parkinson’s disease. It was first approved by the FDA in 1976 and remains a staple for specific neurological and viral indications.
TL;DR
- Typical amantadine dosage for Parkinson’s is 100mg twice daily; for flu prophylaxis it’s 200mg once daily.
- Take tablets whole with water; adjust dose if kidney function is reduced.
- Common side effects include dizziness, insomnia, and a mottled skin rash called livedo reticularis.
- Watch for interactions with anticholinergics, other dopaminergic drugs, and MAO‑inhibitors.
- Brand name Symmetrel is the most widely distributed commercial formulation.
How Amantadine Works: Mechanism of Action
The drug has a dual‑action profile. First, it blocks the NMDA receptor a glutamate‑gated ion channel involved in excitatory neurotransmission, which reduces excitotoxic damage in the brain. Second, it promotes the release of dopamine a neurotransmitter essential for motor control, thereby improving motor symptoms in Parkinson’s disease a neurodegenerative disorder characterized by tremor, rigidity, and bradykinesia. These mechanisms also give amantadine modest activity against Influenza A a viral strain responsible for seasonal flu outbreaks by interfering with viral uncoating.
Approved and Off‑Label Indications
Regulatory agencies list two primary uses:
- Adjunct therapy for Parkinson’s disease, especially to control levodopa‑induced dyskinesias.
- Prophylaxis and early treatment of uncomplicated Influenza A infections.
Clinicians also prescribe amantadine off‑label for drug‑induced extrapyramidal symptoms, traumatic brain injury‑related fatigue, and certain forms of restless‑leg syndrome, leveraging its dopaminergic boost.
Dosage Guidelines
Dosage must be tailored to the indication and patient characteristics. Below is a quick reference:
- Parkinson’s disease: Start with 100mg once daily; increase to 100mg twice daily after 1-2 weeks if tolerated.
- Influenza A prophylaxis: 200mg once daily, begun 1day before exposure and continued for up to 6weeks.
- Influenza A treatment: 200mg on day1, then 100mg twice daily for 4days.
- Pediatrics: Not recommended under 12years; weight‑based dosing only in clinical trials.
For patients with impaired renal function (creatinine clearance <50mL/min), reduce the total daily dose by 50% and monitor serum levels if possible.
Administration Tips and Practical Considerations
Amantadine tablets should be swallowed whole with a full glass of water. Food does not significantly affect absorption, so timing can be flexible, but taking the dose with the same meal each day helps maintain steady plasma levels. Avoid crushing or chewing the tablets; the extended‑release formulation (if used) must not be split.
When prescribing to elderly patients, start at the low end of the dosing range and titrate slowly to minimize central nervous system side effects.
Side Effect Profile: What to Expect
Most patients tolerate amantadine well, but several adverse effects are common enough to warrant mention:
- Dizziness or light‑headedness - often resolves after 1-2weeks.
- Insomnia - advise taking the dose early in the day.
- Livedo reticularis - a mottled, net‑like skin discoloration seen in up to 5% of users.
- Dry mouth and constipation - can be mitigated with adequate hydration and fiber.
- Psychiatric symptoms - rare cases of hallucinations or agitation, especially in patients with pre‑existing cognitive impairment.
Severe reactions such as anaphylaxis or Stevens‑Johnson syndrome are exceedingly rare but require immediate medical attention.
Drug Interactions and Contra‑Indications
Because amantadine influences dopaminergic pathways, it can amplify the effects of other anticholinergic medications that block acetylcholine receptors used in Parkinson’s therapy, potentially leading to excessive cholinergic blockade. Concurrent use with other dopaminergic agents (e.g., pramipexole, ropinirole) may increase the risk of dyskinesia.
Patients taking MAO‑inhibitors mono‑amine oxidase inhibitors that affect neurotransmitter metabolism should avoid amantadine because of unpredictable serotonergic effects.
Contra‑indications include known hypersensitivity to amantadine or any of its excipients, severe renal failure (creatinine clearance<30mL/min), and active psychosis.
Comparing Antiviral Options for Influenza A
| Drug | Mechanism | Standard Adult Dosage | Main Indication | Key Side Effects |
|---|---|---|---|---|
| Amantadine | NMDA‑receptor antagonist & dopamine releaser | 200mg once daily (prophylaxis) or 100mg BID (treatment) | Influenza A prophylaxis; Parkinson’s disease adjunct | Dizziness, insomnia, livedo reticularis |
| Rimantadine | Similar to amantadine - blocks viral uncoating | 100mg once daily | Influenza A prophylaxis (limited by resistance) | GI upset, CNS irritation |
| Oseltamivir | Neuraminidase inhibitor - prevents viral release | 75mg twice daily for 5days | Influenza A & B treatment & prophylaxis | Nausea, vomiting, neuropsychiatric events (rare) |
Choosing the right antiviral hinges on virus susceptibility, patient comorbidities, and the side‑effect tolerance profile. Amantadine shines when the therapeutic goal includes motor symptom control.
Related Concepts and Next Steps in the Medication Cluster
This article sits within a broader medication knowledge cluster that includes:
- Antiviral pharmacology - how drugs like oseltamivir, zanamivir, and baloxavir target different stages of the viral life cycle.
- Parkinson’s disease drug classes - levodopa, MAO‑B inhibitors, and anticholinergics.
- Renal dosing adjustments - principles that apply to many neuro‑active agents.
If you’ve finished with amantadine, you might explore “How to manage levodopa‑induced dyskinesia” or “Current guidelines for seasonal flu prophylaxis.”
Frequently Asked Questions
What is the usual starting dose of amantadine for Parkinson’s disease?
Clinicians typically begin with 100mg once daily and increase to 100mg twice daily after 1-2weeks if the patient tolerates it.
Can I take amantadine if I have mild kidney problems?
Yes, but the total daily dose should be reduced by about 50% when creatinine clearance falls below 50mL/min. Monitoring for side effects becomes especially important.
Is amantadine effective against modern influenza strains?
Its efficacy is limited to influenzaA strains that remain sensitive. Widespread resistance has reduced its use in many regions, so clinicians often prefer neuraminidase inhibitors unless susceptibility testing confirms activity.
What should I do if I develop livedo reticularis while on amantadine?
The rash is usually benign and resolves after discontinuation. If it’s bothersome, talk to your prescriber about dose reduction or switching to an alternative antiviral.
Are there any foods or beverages I must avoid with amantadine?
No specific dietary restrictions exist. However, avoid alcohol or sedatives that could worsen dizziness and CNS depression.
How long can I stay on amantadine for flu prophylaxis?
Guidelines suggest a maximum of six weeks for seasonal prophylaxis. Longer courses increase the risk of resistance and side effects.
Is amantadine safe during pregnancy?
Animal studies show some risk, and human data are limited. The drug is classified as Pregnancy Category C, so it should only be used if the potential benefit justifies the risk.