Some Flu Viruses Resist Drugs

April 3, 2007 -- Some flu viruses appear to resist the antiviral flu drugs Tamiflu and Relenza, report Japanese researchers.

They included Shuji Hatakeyama, MD, PhD, a virus expert at the University of Tokyo.

Hatakeyama and colleagues had previously noted cases of influenza type A that resisted Tamiflu. Now, they note cases of influenza type B that show reduced sensitivity to Tamiflu and Relenza.

Hatakeyama's team studied flu viruses from a Japanese epidemic of influenza type B from 2004 to 2005.

The flu specimens came from patients including 74 children who took Tamiflu for five days, 282 untreated children, and 66 untreated adults.

One of the children who took Tamiflu had influenza type B that resisted Tamiflu and Relenza, according to the researchers' lab tests.

Seven untreated patients had influenza type B that resisted Tamiflu and Relenza, the study shows.

The drug-resistant flu had the same symptoms and duration as normal flu.  Drug-resistant flu likely spread through the community or among siblings, note the researchers.

Drug resistance in influenza type B seems to be rarer than drug resistance in influenza type A but requires "continued close monitoring," write Hatakeyama and colleagues.

Experts who wrote a journal editorial agree that drug-resistant flu should be watched closely.

The news about drug-resistant flu "is not good," states the editorial. But "an effective response to this news can help contend with the new challenges of influenza," write the editorialists.

They included Anne Moscona, MD, of the pediatrics, microbiology, and immunology departments at Weill Medical College of New York's Cornell University.

The study and editorial appear in The Journal of the American Medical Association.

Tamiflu is made by Roche Laboratories. Relenza is made by GlaxoSmithKline. Both are WebMD sponsors.

In the journal, the editorialists note financial ties to drug companies including Roche and GlaxoSmithKline. The Japanese researchers report ties to other drug companies, but not Roche or GlaxoSmithKline.