Chemically, it is a unique tricyclic amine unrelated to any nucleic acid precursor, but inhibits replication of influenza A virus. the activity of amantadine is strain specific, influenza b is not affected. H5N1 and H1N1 strains of Influenza A are resistant in most areas. it appears to act an early step (possibly uncoating) as well as at a late step (viral assembly) in viral replication. protein designated M2 which acts as an Ion channel has been identify as one of is targets of action. Resistance to amantadine develops by mutation causing amino acid substitutions in the M2 protein.