Type B flu virus resistance to Tamiflu and Relenza

Japan has been known for prescribing antiviral flu drugs more frequently than other countries and now one of the less common strains of flu has shown hints of resistance to Tamiflu and Relenza among patients in a small study of patients who had type B influenza.

Type B is normally milder and causes smaller outbreaks than the more common type A.

The findings indicate that doctors may eventually need new medications to treat drug-resistant flu if the viruses become more prevalent.

Previous studies, including work by the same researchers, have found a few cases of resistance to Tamiflu in type A flu, the variety thought most likely to cause a pandemic if bird flu mutates into a human transmissable form.

Dr. William Schaffner, an infectious-disease specialist at Vanderbilt University who was not involved in the study, said Japanese doctors prescribe anti-flu drugs perhaps too often, giving viruses a chance to evolve.

''We were afraid this might happen.'' Schaffner said.

Tamiflu and Relenza, designed to treat seasonal flu, are thought likely to be helpful in treating a global epidemic but this finding confims the importance of vaccination and other preventive measures.

The U.S. government has stockpiled Tamiflu and Relenza, and has funded new anti-flu drug development.

Evolving resistance among viruses is of course biologically inevtiable when doctors use anti-viral drug widely which is why the continual development of new drugs is vital.

The study appeared in Wednesday's Journal of the American Medical Association. Samples from 74 children before and after they were treated with Tamiflu showed drug-resistant virus in one of the children after treatment, indicating the resistance had emerged during treatment.

Samples from 422 untreated children and adults with flu showed drug-resistant virus in seven patients.

The rate of resistance to this family of drugs, less than 2 percent, was lower than for type A influenza where drug-resistant type A virus has been reported at 18 percent.

Note that the study had financial support from the Japanese and U.S. governments. Some researchers reported receiving speaking fees or previous grant support from drug companies, including a company developing a new anti-flu drug.