Rimantadine (INN, sold under the trade name Flumadine) is 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. Rimantadine can mitigate symptoms, including fever. Both rimantadine and the similar drug amantadine are derivates of adamantane. Rimantadine is found to be more effective than amantadine because when used the patient displays fewer symptoms. Rimantadine was approved by the Food and Drug Administration (FDA) in 1994. Rimantadine was approved for medical use in 1993. Seasonal H3N2 and 2009 pandemic flu samples tested have shown resistance to rimantadine, and it is no longer recommended to prescribe for treatment of the flu. Medical use
Influenza A
Rimantadine inhibits influenza activity by binding to amino acids in the M2 transmembrane channel and blocking proton transport across the M2 channel. Rimantadine is believed to inhibit influenzas viral replication, possibly by preventing the uncoating of the viruss protective shells, which are the envelope and capsid. The M2 channel is known to be responsible for viral replication in the influenza virus. 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.Rimantadine is bound inside the pore to amantadine specific amino acid binding sites with hydrogen binding and van der Waals interactions.
The ammonium group (with neighboring water molecules) is positioned towards the C terminus with the amantadane group is positioned towards the N-terminus when bound inside the M2 pore. Influenza resistance
Resistance to rimantadine can occur as a result of amino acid substitutions at certain locations in the transmembrane region of M2. This prevents binding of the antiviral to the channel.The mutation S31N binding site with rimantadine is shown in the image to the left. It shows rimantadine binding into lumenal (top) or peripheral (bottom) binding sites with influenza M2 channel Serine 31 (gold) or Asparagine 31 (blue). Rimantadine enantiomers interactions with M2
Rimantadine, when sold as flumadine, is present as a racemic mixture; the R and S states are both present in the drug. Solid state NMR studies have shown that the R enantiomer has a stronger binding affinity to the M2 channel pore than the S-enantiomer of rimantadine. Antiviral assay and electrophysiology studies show that there is no significant difference between the R and S enantiomers in binding affinity to amino acids in the M2 channel. Since the enantiomers have similar binding affinity, they also have similar ability to block the channel pore and work as an effective antiviral. Rimantadine enantiomers R and S are pictured interacting with the M2 pore below to the right. This image shows that there is not a significant modeled difference between the R and S enantiomers.