A virologist who has treated H5N1 avian influenza patients in Vietnam said the antiviral drug oseltamivir may help avian flu patients even when started later than 2 days after illness onset—generally considered too late, according to a Reuters report today.

The standard advice about oseltamivir for treatment of seasonal flu is that it can shorten the illness if it is started within 2 days after the first symptoms. But Menno de Jong of the Hospital for Tropical Diseases in Ho Chi Minh City said the drug seemed to help four of his patients even though it was started later.

De Jong said the assumption that oseltamivir works only if started within 48 hours may be true only for human flu viruses. He said the H5N1 virus is known to continue replicating in humans on the seventh or eighth day of symptoms.

"In my experience, there is a clear suggestion that there was still virus replication [when we made] a late start in treatment," de Jong told Reuters at a conference in Singapore. "In four of my patients, there was very rapid clearance of the virus from the throat and all four survived."

De Jong told the conference audience, "If you can decrease the viral load [with drugs], you can have a good outcome. Even those who are treated late had good results."

But the report didn´t mention any other evidence that late treatment can work, besides de Jong´s anecdotal findings in a few of his own patients.

De Jong, who treated 17 H5N1 patients in 2004 and 2005, of whom 12 died, agreed with other experts that starting treatment early is still best, Reuters reported.

The United States and many other countries have been stockpiling oseltamivir in the face of the risk that avian flu will spark a pandemic. No one knows how effective the drug will be if the virus evolves into a pandemic strain.

The World Health Organization (WHO) recommends oseltamivir as first-line treatment for H5N1 avian flu (with zanamivir [Relenza] as the second choice). The WHO guidelines do not say that treatment must be started within the first 2 days of illness to be effective.

The US Centers for Disease Control and Prevention says oseltamivir and zanamivir have been shown to reduce the duration of seasonal flu by about 1 day, provided treatment is begun within 48 hours of the first symptoms.

See also:

WHO guidelines on pharmacologic management of patients infected with H5N1
http://www.who.int/csr/disease/avian_influenza/guidelines/pharmamanagement/en/index.html

CDC info on indications for antiviral treatment of patients with flu
http://www.cdc.gov/flu/professionals/treatment/indications.htm