DRUG CLASS AND MECHANISM: Amantadine is a synthetic (man-made) anti-viral drug that can inhibit the replication of viruses in cells. To prevent a viral infection, the drug should be present before exposure to the virus. Clearly, this is not practical for most viral infections. It was initially used to prevent influenza A during flu season, and, if given within 24 to 48 hours of the onset of flu symptoms, to decrease the severity of the flu. Later amantadine was found to cause improvement in the symptoms of Parkinson`s disease. Amantadine`s mechanism of action in Parkinson`s disease is not fully understood. Its effects may be related to its ability to augment (amplify) the effects of dopamine, a neurotransmitter in the brain, that is reduced in Parkinson`s disease. Amantadine is less effective than levodopa in Parkinson`s disease but can offer additional benefit when taken with levodopa. Amantadine was approved by the FDA in 1966.