Since influenza is caused by a virus, antibiotics have no
effect on the infection; unless prescribed for secondary infections such
as bacterial pneumonia. Antiviral medication can be effective, but some
strains of influenza can show resistance to the standard antiviral
The two classes of antiviral drugs used against influenza
are neuraminidase inhibitors and M2 protein inhibitors (adamantane
derivatives). Neuraminidase inhibitors are currently preferred for flu
virus infections since they are less toxic and more effective.
The CDC recommended against using M2 inhibitors during the
2005–06 influenza season due to high levels of drug resistance. As
pregnant women seem to be more severely affected than the general
population by the 2009 H1N1 influenza virus, prompt treatment with
anti-influenza drugs has been recommended.
Antiviral drugs such as oseltamivir (trade name Tamiflu) and
zanamivir (trade name Relenza) are neuraminidase inhibitors that are
designed to halt the spread of the virus in the body.
These drugs are often effective against both influenza A and
Different strains of influenza viruses have differing
degrees of resistance against these antivirals, and it is impossible to
predict what degree of resistance a future pandemic strain might have.
M2 inhibitors (adamantanes)
The antiviral drugs amantadine and rimantadine block a viral
ion channel (M2 protein) and prevent the virus from infecting cells.
Measured resistance to amantadine and rimantadine in
American isolates of H3N2 has increased to 91% in 2005.
This high level of resistance may be due to the easy
availability of amantadines as part of over-the-counter cold remedies in
countries such as China and Russia, and their use to prevent outbreaks
of influenza in farmed poultry.
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