Dosage and Mechanism of Action
A starting dose is often 100 mg once daily. All influenza B strains, many influenza A strains (and virtually all H1N1 "swine flu" strains) are resistant to amantadine, so a failure at this dose is likely due to resistance and not underdosing. For its anti-Parkinsonian effects, a starting dose of 300 mg once daily is normal, but can be increased to a limit of about 400 mg.
The mechanisms for amantadine's antiviral and antiparkinsonian effects appear to be unrelated.
- The mechanism of Amantadine's antiviral activity involves interference with a viral protein, M2 (an ion channel), which is required for the viral particle to become "uncoated" once taken inside a cell by endocytosis.
- The mechanism of its antiparkinsonian effect is poorly understood. The drug has many effects in the brain, including release of dopamine and norepinephrine from nerve endings. It appears to be a weak NMDA receptor antagonist as well as an anticholinergic, specifically a nicotinic alpha-7 antagonist like the similar pharmaceutical memantine.
Amantadine appears to act through several pharmacological mechanisms, but no dominant mechanism of action has been identified. It is a dopaminergic, noradrenergic and serotonergic substance, blocks monoamine oxidase A and NMDA receptors, and seems to raise beta-endorphin/beta-lipotropin levels.
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