Posted on 09/22/2005 5:51:04 AM PDT by Mother Abigail
Human influenza viruses becoming resistant to class of flu drugs: CDC study
Helen Branswell
Canadian Press
September 22, 2005
TORONTO (CP) - Human flu viruses are becoming increasingly resistant to the class of drugs known as adamantanes, one of only two existing classes of flu drugs, a new study released Thursday shows.
The authors say their findings call into question the future usefulness of the adamantane or M2 inhibitor drugs - a warning echoed by a leading antiviral expert who was not involved in the work.
That independent expert, Dr. Frederick Hayden suggested that in light of the findings the drugs amantadine and rimantadine should not play a significant role in drug stockpiles put together to help a country weather a flu pandemic.
"I think that these data present real concerns about how can we use this class in the future. And it certainly says it makes little sense to make it an important part of drug stockpiles for pandemic response," said Hayden, a scientist at the University of Virginia who is on secondment to the World Health Organization.
"It takes one of the arrows out of our quiver, as it were."
Only one of the drugs, amantadine, is sold in Canada. The Public Health Agency of Canada has plans to add substantial quantities of the drug to the country's pandemic stockpile.
The M2 inhibitors are off-patent and much cheaper than the only other class of flu drugs, the patent-protected neuraminidase inhibitors oseltamivir (Tamiflu) and zanamivir (Relenza).
The first author of the study was less definitive about the future of the drug, saying he felt it was too soon to consider the class lost for good.
"It's hard to tell. We don't know exactly what caused the resistance. And it's possible that if it was caused by a spontaneous mutation the virus could mutate and go back the other way," said Rick Bright of the strain surveillance section of the influenza branch at the U.S. Centers for Disease Control in Atlanta.
"I certainly wouldn't give up hope on any class of (flu) drugs at this point."
But the paper itself warns agencies and governments purchasing pandemic stockpiles that amantadine and rimantadine "will probably no longer be effective for treatment or prophylaxis" - using the drugs to ward off illness - "in the event of a pandemic outbreak of influenza."
Bright and his co-authors analysed human flu viruses submitted to the CDC - in its role as a WHO influenza reference laboratory - between Oct. 1, 1994 and March 31, 2005. The aim was to see if the rates of resistance to the adamantane drugs changed over that period.
The scientists screened more than 7,000 human influenza A viruses looking for specific genetic mutations known to confer resistance to the adamantane drugs.
Rates of resistance started to rise in China in 2000 and spiked between 2002 and 2003. Additional spikes occurred in 2003 in viruses from Hong Kong, Taiwan and South Korea.
"Viruses collected in 2004 from South Korea, Taiwan, Hong Kong and China showed drug-resistance frequencies of 15 per cent, 23 per cent, 70 per cent and 74 per cent respectively," they wrote in the article, published by the medical journal The Lancet.
And in the distance, dark clouds and warnings. Will this storm of confluence pass us by - or visit us with fury?
"Thou the spring of all my comfort,
More than life to me,
whom have I on earth beside thee?
Whom in heaven but thee?"
MA
Bush's fault.
IF they can get a good handle on the last mutations. IF the trials and FDA approvals can be done in time, then maybe.
I wouldn't be on it.
Thanks for posting this.
Are all the vaccines part of the problem?
Vaccines always "help"
a virus. Evolution
goes faster for them
than for us. Vaccines
kill some strains of virus, but
the survivors will
live to dominate.
The question then always is
will surviving strains
also be deadly
as the strains killed. You can't tell
until they evolve.
"From the perspective of a microbe, anti-bacterial and anti-viral drugs are selection pressures. They present the pathogen with a range of hostile environments. Given this, those microorganisms that have through chance mutation or recombination acquired traits that resist these selection pressures have a great advantage. While all their fellow organisms might be destroyed, they survive. Thus it is more likely that their genes for resisting these hostile environments will be passed on to the next generation."
Emerging Diseases : Biological Terrorism : Biological Warfare
Please note, I am talking about vaccines, not antiviral drugs. The have different effects on the selection pressure and hence the evolution of the virus.
Thank you for keeping us informed of this.
I think this article explains a reason for this resistance.
By Peter Goff in Beijing
(Filed: 19/06/2005)
China has been trying to suppress a bird flu outbreak by feeding poultry a human antiviral drug, threatening public safety in the event of a global pandemic.
China first reported an avian flu outbreak in February last year. Yet for more than eight years, according to drug company officials in Beijing quoted in the US media, the agriculture ministry has been urging farmers to use the drug, amantadine, on infected birds, in breach of international guidelines.
It explains why scientists discovered late last year that the virus had grown resistant to amantadine, which cannot now be used to fight it in humans
"But at my back I always hear
Time's winged chariot hurrying near"
....Andrew Marvell
Thanks for the ping. I have nothing I can contribute right now, but I continue to monitor.
Thanks again.
bump for later
Rates of resistance started to rise in China in 2000 and spiked between 2002 and 2003. Additional spikes occurred in 2003 in viruses from Hong Kong, Taiwan and South Korea.
And are these individuals being given sufficient quantities of the antivirals in question? I have my doubts.
I think it was Dr. Niman who suggested that since Tamiflu and Amantadine target viruses differently, they could be used in combination in the event of H5N1 outbreaks. I know about the resistance studies, but I'm wondering if there have been or will have been enough changes in the virus to suggest a use for Amantadine and Relenza.
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