Older antiviral drugs amantadine and rimantidine should not be used to treat seasonal or pandemic influenza because they are not very effective and have serious side-effects, scientists said on Thursday.

And newer drugs including Relenza and Tamiflu should only be used in serious flu epidemics and to fight bird flu with other preventive measures such as masks.

But Dr Tom Jefferson and researchers of the Cochrane Collaboration, who reviewed more than 50 trials of the drugs, said they found no evidence that Relenza, which is sold by GlaxoSmithKline, or Roche’s Tamiflu are effective against avian influenza.

“These drugs should not be used routinely for seasonal influenza in the absence of a certain diagnosis of influenza A and B. We couldn’t find any evidence of their effect on avian flu,” Jefferson said in an interview.

“They may or may not work (against avian flu),” he added.

Governments around the globe are stockpiling Tamiflu and Relenza in case the H5N1 avian flu virus mutates into a pandemic strain that could become highly infectious in humans.

In response to the review, Roche said Tamiflu’s approval was based on the treatment and prevention of seasonal influenza.

“To state that the drugs are not suitable for routine influenza control is entirely inappropriate, is inconsistent with regulatory opinions worldwide and is not supported by the data,” said David Reddy, the company’s flu pandemic taskforce head, in a conference call.

RESISTANCE

The researchers reviewed trials published during the past 40 years that assessed drugs against influenza and its complications and influenza-like illnesses.

Influenza is caused by influenza A or B virus while influenza-like illness can be caused by a variety of different viruses.

The findings of the Cochrane Review, which are published online by The Lancet medical journal, come less than a week after health officials in the United States advised doctors to stop using the older flu drugs.

Jefferson and his team said both the older and newer drugs prevented or eased symptoms of influenza but they did not prevent infection. None of the drugs was effective against influenza-like illnesses.

Amantadine and rimantidine also caused side effects such as hallucinations and agitation. The use of amantadine was linked to rapid viral resistance.

The researchers expressed concern about use of the newer drugs against seasonal influenza because of concerns about resistance.

“There is increasing evidence that widespread use of neuraminidase inhibitors in countries like Japan is causing increasing resistance,” Jefferson said.

The review also found that the newer drugs do not stop the virus being shed by an infected person, so people can catch the flu from someone who is being treated.

Jefferson said if Tamiflu and Relenza are used to control a serious epidemic or pandemic, other measures such as masks, gowns, gloves, quarantine and hand-washing will be needed to prevent its spread.

The Cochrane Collaboration is an international, independent organization that provides regular reviews about the effects of healthcare measures.