Laboratory methodologies for testing the antiviral susceptibility of influenza viruses:
M2 ion channel inhibitor
Approaches to M2 inhibitor resistance testing
M2 inhibitor resistance is associated with amino acid substitutions, due to single-nucleotide polymorphism (SNP) between residues 26-34 in the transmembrane domain of the M2 protein. The most commonly detected M2 amino acid substitution that confers M2 inhibitor resistance is S31N.
The frequency of M2 inhibitor resistance in currently circulating seasonal influenza A viruses is very high (>99%) . The M2 inhibitors are also ineffective against influenza B viruses. Consequently, WHO does not recommend the use of the M2 inhibitors for the treatment of patients infected with circulating seasonal influenza viruses.
M2 inhibitor resistance testing is thus not considered a priority activity for National Influenza Centres in GISRS.