-- Robert Preidt
TUESDAY, Dec. 7 (HealthDay News) -- Certain influenza virus
strains are developing increasing drug resistance and greater
ability to spread, a new study warns.
American and Canadian researchers confirmed that resistance to
the two approved classes of antiviral drugs can occur in several
ways and said this dual resistance has been on the rise over the
past three years.
The team analyzed 28 seasonal H1N1 influenza viruses that were
present in five countries from 2008 to 2010 and were resistant to
both M2 blockers (adamantanes) and neuraminidase inhibitors (NAIs),
including oseltamivir and zanamivir.
The researchers found that additional antiviral resistance can
rapidly develop in a previously single-resistant influenza virus
through mutation, drug response, or gene exchange with another
The study also found that the proportion of tested viruses with
dual resistance increased from 00.6 percent in 2007-08 to 1.5
percent in 2008-09 and 28 percent in 2009-10.
The findings are published online Dec. 7 in advance of print
publication Jan. 1 in the
Journal of Infectious Diseases.
"Because only two classes of antiviral agents are approved, the detection of viruses with resistance to drugs in both classes is concerning," study author Dr. Larisa Gubareva, of the U.S. Centers for Disease Control and Prevention, said in a journal news release.
"If circulation of these viruses with dual resistance becomes more widespread among any of the predominant circulating influenza A viruses, treatment options will be extremely limited," she added. "New antiviral agents and strategies for antiviral therapy are likely to be necessary in the future."
Another study in the same issue of the journal examined an
outbreak of oseltamivir-resistant pandemic H1N1 influenza in a
hematology unit in a British hospital. The researchers concluded
"that oseltamivir may not be the frontline drug of choice in
hematology patients, and zanamivir may prove to be more
In an editorial accompanying the two studies, experts said
increased monitoring and creative prevention and treatment choices
will be needed as unpredictable and antiviral-resistant influenza
viruses continue to appear.
With only two classes of antiviral drugs approved for use in
most countries, future research should focus on the effectiveness
of zanamivir and combination antiviral therapy and the development
of new types of antiviral drugs, wrote Dr. Frederick G. Hayden, of
the University of Virginia School of Medicine, and Dr. Menno D. de
Jong, of the University of Amsterdam in the Netherlands.
The U.S. National Institute of Allergy and Infectious Diseases
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