Resistant an influenza virus to drugs

By Vibha Varshney
Published: Wednesday 15 August 2007

rational use of drugs may not always delay resistance to a drug. A research team led by the National Institutes of Health in the us has found that the influenza virus h3n2 were resistant to drugs belonging to the adamantane group irrespective of whether they were exposed to the drug or not. Examining an international collection of viral genomes, they found a single type of mutation was responsible for every case of resistance.

They say resistance to the drug was developing in the virus as a natural process by which the virus developed into an effective organism. The frequency of resistance to adamantane drugs has now increased from about 2 per cent to 90 per cent around the world. For example, viruses in the us, where an average of 1.5 million adamantane dosages was prescribed annually, and countries like New Zealand and Japan, where the drug is rarely used, were resistant to the drug.
Drug is not enough This resistance can be attributed to a single replacement of an amino acid. "The study shows drug resistance can evolve by unusual means," says Edward C Holmes, Center for Infectious Disease Dynamics, Department of Biology, Pennsylvania State University.

"The resistance mutation gets linked to another beneficial mutation located elsewherein the viral genome. The increasing use of the drug does not lead to this resistance. So stopping the use of the drug will not reduce resistance," he adds. The accepted theory about drug resistance is that if the virus is exposed to the drug, only those that are resistant to it survive, making the drug ineffective in the future. The new research shows the virus would become resistant regardless to exposure, suggesting that strategies involving careful drug use might not work. This implies that adamantanes may not be useful for treating influenza viruses in the long run. The paper was published online on May 23, 2007, in the journal Molecular Biology and Evolution.

In January 2006, the us Center for Disease Control and Prevention announced that amantadine and another drug rimantadine should not be used for such treatment. Instead, the agency recommended using oseltamivir (Tamiflu) or zanamivir (Relenza). Adequate rest and abstaining from alcohol can help check flu. Experts say that anti-viral medicines are recommended only if there is a risk of complication.

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