Amantadine and Rimantadine (Adamantanes)
Adamantane resistance among circulating influenza A viruses
increased rapidly worldwide beginning during 2003–2004. The
percentage of influenza A virus isolates submitted from throughout
the world to the World Health Organization Collaborating Center for
Surveillance, Epidemiology, and Control of Influenza at CDC that
were adamantane-resistant increased from 0.4% during 1994–1995
to 12.3% during 2003–2004 (137). During the 2005–06 influenza
season, CDC determined that 193 (92%) of 209 influenza A (H3N2)
viruses isolated from patients in 26 states demonstrated a change at
amino acid 31 in the M2 gene that confers resistance to adamantanes
(138). Resistance to adamantanes remains high among influenza A
isolates, with resistance detected among all tested influenza A (H3N2)
and 2009 H1N1 viruses tested (113). Therefore, amantadine and
rimantadine are not recommended for antiviral treatment or chemoprophylaxis
of currently circulating influenza A virus strains.