amantadine, drug used to treat infections caused by influenza type A virus, the most common cause of influenza epidemics. Amantadine and its derivative, rimantadine, can be used successfully in the prevention and treatment of influenza A; however, these agents have no effect against influenza B viruses. Amantadine also has some ability to reduce symptoms of tremor and bradykinesia (slowness of movement) in patients affected by Parkinson disease.
In the treatment of influenza, amantadine acts by blocking uncoating of the virus within the cell, thus preventing the release of viral RNA into the host cell. Amantadine can also block the assembly of influenza virus during viral replication. Mutations in some strains of influenza A virus can render the virus resistant to amantadine; however, these mutations do not appear to increase virulence. In the treatment of Parkinson disease, amantadine appears to work through multiple mechanisms. The drug can stimulate the release of dopamine from certain cells in the brain and can block the receptors of excitatory molecules involved in causing overactivity of neurons that control movement.
Administration of amantadine may cause gastrointestinal upset. The drug also may have minor effects on the central nervous system, resulting in dizziness or confusion. Abnormally high plasma concentrations of amantadine may elicit symptoms of neurotoxicity and cause seizures and coma. These effects can also be caused by the administration of anticholinesterases or antihistamines while taking amantadine.