Misuse led to drug-resistant flu strains -experts
CHICAGO (Reuters) – Misuse of two anti-viral drugs in
China, Russia and other countries likely led to the development
of resistant influenza strains against which the drugs are now
nearly useless, health experts said on Thursday.
The medicines involved are amantadine and rimantadine, used
to treat common seasonal influenza but not intended to combat
the avian flu strain that has killed at least 85 people since
2003 and which experts fear could mutate and cause a global
pandemic.
Last month the U.S. Centers for Disease Control and
Prevention said 120 samples of the most prevalent flu strain in
the country this season showed it was resistant to amantadine
and rimantadine in 91 percent of cases. The resistance level
was only 11 percent the previous flu season.
David Weinstock and Gianna Zuccotti, two doctors at
Memorial Sloan-Kettering Cancer Center, New York, said that
development was “a clarion call for action from the medical
community.”
“The rate of adamantane resistance began to increase in
Asia in the 1997-1998 influenza season and increased markedly
in China to 57 percent in 2002-2003 and 73 percent in
2003-2004,” they said. Adamantane describes the class of drugs
to which amantadine and rimantadine belong.
“Misuse of adamantanes most likely contributed to this
rapid increase in resistance,” they added. “In China, Russia
and some other countries, amantadine and rimantadine are both
available without a prescription and are included in
over-the-counter ‘antiflu’ and ‘cold’ preparations at a range
of doses.”
Viral or bacterial agents can adapt and become resistant to
drugs used to treat them when the drugs are overused or not
taken appropriately.
Weinstock and Zuccotti urged doctors and health care
professionals to educate patients and communities, organize an
international response and work against the release of
over-the-counter antiviral drugs, either directly by major drug
companies or through licensing agreements with generic
manufacturers.
They made the comments in an editorial accompanying a
report from the CDC, both of which are to be published in next
week’s Journal of the American Medical Association.
In the CDC study, researchers said the resistance is
widespread and affects flu strains in all regions of the United
States and other areas of North America as well.
The CDC last month urged doctors not to use the two drugs
to prevent flu or to treat patients suspected of having it
because the drugs are no longer effective. Doctors instead
should prescribe either of two newer medicines, Tamiflu or
Relenza, which still fight the strain, the agency said. Tamiflu
is made by Roche Holding AG and Relenza by GlaxoSmithKline Plc.