Amantadine is used primarily as what type of agent in humans?

Amantadine is primarily recognized as an antiviral agent in humans. It was originally developed to treat influenza A infections and is effective in preventing and treating this type of viral infection by inhibiting the replication of the virus. Additionally, amantadine has been shown to have beneficial effects in treating certain movement disorders, such as Parkinson's disease, although its antiviral properties remain its primary use.

In the context of this question, the choice regarding amantadine being an analgesic, anticonvulsant, or antidepressant does not align with its established uses. An analgesic would be used for pain relief, an anticonvulsant for managing seizures, and an antidepressant for treating mood disorders. While amantadine can influence other systems in the body, its primary and most recognized role is in the realm of antiviral therapy.