THURSDAY, Aug. 26, 2004 (HealthDayNews) -- A small Japanese study suggests that influenza viruses are becoming resistant to Tamiflu, a widely used drug that eases the flu's symptoms, and that the resistance may be more common than thought.
Many doctors prescribe the antiviral drug Tamiflu (generic name oseltamivir) to people 1 year and older who have flu symptoms for more than two days.
In the new study, 18 percent of the child patients had Tamiflu-resistant influenza, said lead researcher Yoshihiro Kawaoka, a professor of virology, microbiology, and immunology at the University of Tokyo.
Tamiflu is a type of drug called a neuraminidase inhibitor. It works by blocking an enzyme that allows the flu virus to infect other cells. Tamiflu is widely used, but to date there has been little independent research into viruses that are resistant to this drug.
The drug was approved for use in the United States in 1999, and its maker, Roche Pharmaceuticals, says that 21 million patients have been treated with it. A company spokesman said that its own research has found that resistance is much lower in both children and adults.
Kawaoka's team studied influenza A viruses from 50 Japanese children, ages 2 months to 14 years, before and during treatment with Tamiflu. Nine of the patients diagnosed with influenza and treated with Tamiflu had drug-resistant viruses, Kawaoka said.
In addition, some of these patients continued to produce influenza viruses even though their clinical symptoms were subsiding, he noted.
Roche pointed out that this study included several children under a year old, and Tamiflu isn't approved for use in this age group.
The report appears in the Aug. 28 issue of The Lancet.
It is unlikely that oseltamivir-resistant viruses will cause outbreaks during annual influenza epidemics, Kawaoka said. However, such resistant viruses may be a problem in a pandemic, where the majority of the population is immunologically unprepared for the new influenza virus, he cautioned.
In light of this finding, Kawaoka believes that children with flu should be kept away from others even after they seem better. Young influenza patients treated with oseltamivir should stay home for a certain period of time, even if their symptoms are improving, to prevent viral transmission to others, he advised.
These new flu drugs (the first was Relenza) have been "a true success story," Dr. Anne Moscona, a pediatrician at Mount Sinai School of Medicine, writes in an accompanying editorial. They help in "preventing and treating a major infectious threat."
She adds that this study should be taken as an mandate to learn more about the incidence and mechanisms of resistance to the neuraminidase inhibitors, so that appropriate strategies can be developed for their use during the next pandemic.
Terry Hurley, a Roche spokesman, said the company's studies have found resistance to be 0.4 percent in adults and less than 4 percent in children under age 12. Moreover, he said in a statement, the Japanese patients "may not have received an adequate dose of Tamiflu."
Based on the fear of a flu pandemic, the Bush administration announced the first national plan for how the country should prepare for and respond to a flu epidemic should it hit the United States, The New York Times reported Thursday.
According to the report, the administration became concerned because of the SARS epidemic and the spread of avian flu in Asia.
The plan lays out the public health measures that would be crucial in the event of a flu pandemic, including the emergency production of vaccines, the stockpiling of antiviral drugs, the freeing up of enough hospital beds to care for the sickest, the limiting of public gatherings, and the possible imposition of quarantines, the Times said.
The federal government has enough Tamiflu for 1 million people. But that would be woefully inadequate to treat enough people in a pandemic, the Times reported.
Dr. Julie L. Gerberding, director of the U.S. Centers for Disease Control and Prevention, said she believed the country needed a stockpile for 100 million people. But Roche, the sole manufacturer of the drug, cannot supply that amount, officials said. The officials said they are seeking help to rank who would get the scarce vaccine and drugs when a pandemic hits, the Times reported.
The American Lung Association has more on the flu.