Children should not routinely be treated with flu drugs like Tamiflu since there is no clear evidence they prevent complications and the medicines may do more harm than good, British researchers said.

They called for a rethink of current widespread use of antivirals among under-12s in the light of an analysis of clinical data from past seasonal flu outbreaks showing scant benefits and potentially harmful side effects.

Governments around the world have built up large stockpiles of Roche's Tamiflu and GlaxoSmithKline's Relenza to deal with the current H1N1 swine flu pandemic.

In Britain, hundreds of thousands of doses of Tamiflu have been handed out to people with the disease, of whom around half are children.

But Dr Matthew Thompson from the University of Oxford said that while antivirals shortened the duration of flu in children by around a day, they didn't reduce asthma flare-ups or the likelihood of children needing antibiotics.

Tamiflu was also linked to an increased risk of vomiting, which can be serious in children as it causes dehydration.

The analysis was based on a systematic review of seven clinical studies looking at use of Tamiflu and Relenza in seasonal flu outbreaks in 2,629 children aged 1 to 12 years.

Thompson said there was no reason to think the conclusions would not also apply to the current relatively mild outbreak of swine flu.

"The strategy of giving out this treatment in a mild infection is inappropriate," fellow Oxford researcher Dr Carl Heneghan told reporters.

"While morbidity and mortality in the current pandemic remain low, a more conservative strategy might be considered prudent, given the limited data, side effects such as vomiting, and the potential for developing resistant strains of influenza," they wrote in the British Medical Journal.

Dr Ronald Cutler at Queen Mary, University of London, who was not involved in the Oxford research, agreed that targeted drug use could be more beneficial than widespread use.

Roche said the side effects of Tamiflu were known but the drug had been shown to prevent flu infection and reduce both the duration and severity of illness.

"In clinical studies of children taking Tamiflu the main adverse events were nausea 4 percent, abdominal pain 1 percent and vomiting 10 percent," it added in a statement.

The most common recorded side effects with Glaxo's inhaled drug Relenza were headache and nausea, the British company said. - Reuters