Amantadine
Summary
Amantadine blocks the influenza A M2 proton channel to prevent viral uncoating, and separately increases dopamine release and blocks NMDA receptors. Its antiviral use is obsolete because of resistance, but it remains useful in Parkinson disease, particularly for levodopa-induced dyskinesia.
Detail
As an antiviral, amantadine inhibits the M2 channel of influenza A only, and near-universal resistance has ended that indication. Its neurological uses rest on different actions: it increases presynaptic dopamine release, decreases reuptake, and antagonizes NMDA glutamate receptors. In Parkinson disease it gives mild symptomatic benefit and is the drug of choice for reducing levodopa-induced dyskinesias; it is also used for drug-induced extrapyramidal symptoms, for fatigue in multiple sclerosis, and in traumatic brain injury. Adverse effects include ataxia, dizziness, insomnia, confusion and hallucinations, especially in the elderly, peripheral oedema, and the characteristic livedo reticularis, a mottled reddish-blue skin discoloration of the legs. Amantadine is excreted unchanged by the kidney, so the dose must be reduced in renal impairment, and it can precipitate delirium in patients with pre-existing cognitive impairment.
Sources
- Katzung Basic and Clinical Pharmacology
- First Aid for the USMLE Step 1
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