It was introduced as an agent for prophylaxis of influenza A and was later found to cause symptomatic improvement in parkinsonism. A virus, it should not be used as a substitute for vaccination. Rimantadine is a related antiviral compound that reaches higher concentrations in respiratory secretions after oral administration and has fewer CNS effects. Amantadine was approved by the FDA in 1966. Amantadine's mechanism of action is not fully understood.
Antiparkinsonian actions are unrelated to the antiviral effects.
Amantadine appears to potentiate CNS dopaminergic responses. It may release dopamine and norepinephrine from storage sites and inhibit the reuptake of dopamine and norepinephrine. Amantadine is clearly less effective than levodopa but can offer additional benefit in patients experiencing maximal or waning effects from levodopa. As an antiviral, amantadine can inhibit viral replication within the viral cell. Amantadine appears to block the uncoating of the virus particle and subsequent release of viral nucleic acid into the host cell.