Dopaminergic / Antiviral (Adamantane Derivative) Pregnancy: Contraindicated during pregnancy and in women trying to become pregnant; amantadine-related complications during pregnancy have been reported. Breastfeeding: amantadine passes into breast milk and undesirable effects have been reported in breastfed infants — nursing mothers should not take amantadine. No human fertility data available.

Amantadine Hydrochloride

Brand names: Lysovir, Symmetrel

Amantadine hydrochloride is an oral agent used in Parkinson's disease, particularly to reduce levodopa-induced dyskinesia, and historically as an antiviral against influenza A.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Parkinson's disease: initially 100 mg daily for the first week, increasing to 100 mg twice daily

Route: Oral

Frequency: Once daily initially, then twice daily

Max: 400 mg/day should not be exceeded

The dose can be titrated against signs and symptoms; increase gradually at intervals of not less than 1 week. Doses exceeding 200 mg daily may provide some additional relief but may also be associated with increasing toxicity. Patients over 65 years tend to have lower renal clearance and higher plasma concentrations, so the lowest effective dose should be used. Amantadine acts within a few days but may appear to lose efficacy within a few months of continuous treatment; effectiveness may be prolonged by withdrawal for three to four weeks, during which existing antiparkinsonian therapy should be continued or low-dose levodopa started if clinically necessary. Withdrawal should be gradual, e.g. halving the dose at weekly intervals — abrupt discontinuation may exacerbate Parkinsonism and has been associated with symptoms resembling neuroleptic malignant syndrome and with cognitive manifestations, and it should not be stopped abruptly in patients also taking neuroleptics. Combined treatment: continue any antiparkinson drug already in use during initial amantadine treatment, then reduce it gradually if possible; in patients on large doses of anticholinergics or levodopa, extend the initial phase of amantadine treatment to 15 days. Monitor for impulse control disorders. IMPORTANT: the fetched SPC (Amantadine hydrochloride 100 mg Capsules) gives posology for Parkinson's disease only — it contains no influenza/antiviral regimen and no post-viral fatigue regimen, so any such dosing shown on this page must be re-sourced from a product licensed for that indication. No paediatric posology is given in this SPC extract; US labelling states that safety and efficacy in newborn infants and infants below 1 year of age have not been established.

Dose adjustments

Renal

Reduce the dose in renal impairment, either by reducing the total daily dose or by increasing the dosage interval according to creatinine clearance: CrCl <15 mL/min — contraindicated; CrCl 15-35 mL/min — 100 mg every 2 to 3 days; CrCl >35 mL/min — 100 mg every day. These are guidance only; continue to monitor for unwanted effects.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to the active substance or to any of the excipients
Individuals subject to convulsions
A history of gastric ulceration
Severe renal disease (creatinine clearance <15 mL/min — amantadine contraindicated)
Pregnancy

Side effects

Oedema of the ankles and livedo reticularis (very common; livedo usually after very high doses or use over many months)
Anxiety, elevation of mood, hallucinations, depression, insomnia, confusion, nightmares, nervousness (common); disorientation and psychosis (rare); impulse control disorders, delirium, hypomania and mania (frequency not known)
Light-headedness, headache, lethargy, ataxia, slurred speech, loss of concentration (common); tremor, dyskinesia, convulsions, neuroleptic malignant-like syndrome (rare)
Dry mouth, anorexia, nausea, vomiting, constipation (common); diarrhoea (rare)
Palpitations, orthostatic hypotension (common); heart insufficiency/failure (very rare)
Blurred vision (uncommon); corneal lesions including punctate subepithelial opacities, superficial punctate keratitis, corneal epithelial oedema and markedly reduced visual acuity (rare) — contact an ophthalmologist if visual problems occur and discontinue if corneal oedema is diagnosed

Interactions

Anticholinergic agents or levodopa — concurrent administration may increase confusion, hallucinations and nightmares (§4.5; the section text is truncated in this source extract, so the interaction list is incomplete)
Other medicines with an effect on the CNS — caution when co-prescribing (§4.4)
Neuroleptics — do not stop amantadine abruptly in patients treated concurrently with neuroleptics (risk of neuroleptic malignant syndrome or neuroleptic-induced catatonia)
US labelling adds: CNS stimulants (careful observation required); thioridazine (reported to worsen tremor in elderly patients with Parkinson's disease); triamterene with hydrochlorothiazide (higher plasma amantadine concentration reported); quinine or quinidine (reduce renal clearance of amantadine by about 30%); live attenuated intranasal influenza vaccine (avoid within 2 weeks before or 48 hours after amantadine unless medically indicated)

Clinical monograph

How it works

It has dopaminergic actions (enhancing dopamine release and blocking reuptake) and NMDA-receptor antagonist activity, which underlies its benefit against dyskinesia.

Prescribing in practice

It can cause confusion, hallucinations and livedo reticularis, and should be withdrawn gradually because abrupt cessation may precipitate an acute confusional state or neuroleptic malignant syndrome-like reaction.
The dose should be reduced in renal impairment as it is largely renally excreted.
Avoid administration late in the day to limit insomnia and vivid dreams.

Monitoring

Monitor for neuropsychiatric effects and review renal function, especially in the elderly.

Counselling the patient

Do not stop the medicine suddenly; it should be reduced gradually.
Report confusion, hallucinations, mood change or ankle swelling.
A purplish mottling of the skin on the legs can occur and is usually reversible on stopping.

Evidence & guidelines

Amantadine is recognised by NICE for managing levodopa-induced dyskinesia in Parkinson's disease.

Reference: NICE NG71 (Parkinson's disease in adults, 2017 updated 2022); Parkinson's UK drug factsheet on amantadine; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways