Misuse led to drug-resistant flu strains -experts
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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.”
Viruses and bacteria 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 the 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.
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