This seasons flu sufferers are being advised to avoid two common antiviral drugs for the treatment of their illness, because the virus -- at least its primary strain -- appears to have become resistant to their effects.
The two drugs are amantadine and rimantadine, which in years past have been effective to treating influenzas A and B.
In new guidelines for the 2005-06 flu seasonm the Centers for Disease Control suggests doctors use Tamiflu and Relenza to combat the flu virus, pointing out there are ample supplies of both anti-virals. The CDC said it's not too late to get a flu shot, and urged consumers to get one if they havent already.
The CDC said viral resistance to adamantanes can emerge rapidly during treatment because a single point mutation at amino acid positions 26, 27, 30, 31, or 34 of the M2 protein can confer cross-resistance to both amantadine and rimantadine. It said the transmissibility of adamantane-resistant viruses is not impaired by any of these amino acid changes.
A recent report on the global prevalence of adamantane-resistant influenza viruses showed a significant increase (from 1.9% to 12.3%) in drug resistance over the past 3 years. In the United States, the frequency of drug resistance increased from 1.9% in 2004 to 14.5% during the first 6 months of the 200405 influenza season.
For the 200506 season, 120 influenza A (H3N2) viruses isolated from patients in 23 states have been tested at CDC through January 12, 2006; 109 of the isolates (91%) contain an amino acid change at position 31 of the M2 protein, which confers resistance to amantadine and rimantadine. Three influenza A(H1N1) viruses have been tested and demonstrated susceptibility to these drugs.
All influenza viruses from the United States that have been screened for antiviral resistance at CDC have demonstrated susceptibility to the neuraminidase inhibitors.
