Rimantadine an orally administered antiviral drug used to treat, and in rare cases prevent, influenzavirus A infection. When taken within one to two days of developing symptoms, rimantadine can shorten the duration and moderate the severity of influenza. Both rimantadine and the similar drug amantadine are derivates of adamantane. Rimantadine is believed to inhibit influenza's viral replication, possibly by preventing the uncoating of the virus's protective shells, which are the envelope and capsid. Genetic studies suggest that the virus M2 protein, an ion channel specified by virion M2 gene, plays an important role in the susceptibility of influenza A virus to inhibition by rimantadine. Resistance to rimantadine can occur as a result of an amino acid substitutions at certain locations in the transmembrane region of M2. This prevents binding of the antiviral to the channel.