Japanese Study finds new Drug Resistant Flu

Type B flu viruses, a less common strain of flu, can mutate to develop resistance to two of the main antiviral drugs Tamiflu and Relenza prescribed to treat seasonal influenza, according to a Japanese study published in the April 4 issue of the Journal of American Medical Association.

Presenting the new and unwelcome evidence, researchers from the University of Tokyo stated that not only type A viruses have the ability to develop a resistance to top line preventative drugs, instead type B flu viruses, which usually cause smaller epidemics than type A, mutates into drug-resistant.

In a small study, the researchers looked at two antiviral drugs Tamiflu, manufactured by Roche this antiviral drug is used in the treatment of both Influenza virus A and Influenza virus B, and Relenza, manufactured by London based GlaxoSmithKline (GSK). Both the drugs are neuraminidase inhibitors, which have been effective against influenza and are used extensively.

Japan is the biggest user of Tamiflu, first orally active neuraminidase inhibitor commercially developed.

To reach their conclusion, Japanese researchers pitted the drugs against a major outbreak of an influenza B that was emerged in Japan in 2004/2005. Researchers collected influenza B isolates from 74 children before and after Tamiflu therapy and from 348 untreated flu patients and upon examining physical data, they noticed that one of the children after treatment had a virus with reduced drug sensitivity.

The researchers further found that influenza B viruses recovered from several people who had not taken flu drugs were partially resistant to Tamiflu, Relenza or both, indicating these less susceptible viruses were spreading at low levels in their communities.

They discovered the variant of the virus that had reduced drug sensitivity in 1.4 percent of the children who had received Tamiflu. Furthermore, they found that 1.7 percent of the flu viruses from untreated patients had reduced sensitivity to Relenza, Tamiflu, or both.

Experts concern if the viruses become more prevalent, doctors will eventually need new medications to treat drug-resistant flu.

"If drug-resistant influenza B viruses become more prevalent, we will need new drugs to treat infected patients," said study co-author Yoshihiro Kawaoka, a virology professor at the University of Tokyo and the University of Wisconsin-Madison.

They examined the prevalence and transmissibility of influenza B viruses with reduced sensitivity to neuraminidase inhibitors in Japan where both Tamiflu and Relenza are used more frequently than anywhere else in the world.

"We are concerned about emerging resistance patterns through overuse of these drugs," said Dr. Marc Siegel, a clinical associate professor of medicine at New York University School of Medicine. "This study is another caution to the overuse of a drug based on fear."

Tamiflu was linked with hallucinations and other abnormal behavior in people taking the medication. In November last, the US Food and Drug Administration (FDA) added new warning label to the drug after receiving more than 100 reports of unusual psychiatric effects, including cases of self-injury and suicide.