Tamiflu, the frontline treatment for influenza, offers no benefit for patients if it is administered in double the normal dose, a study conducted in Southeast Asia said on Thursday.

Previous studies that found Tamiflu -- lab name oseltamivir -- is more effective if administered swiftly after infection, have prompted suggestions that patients would also do better if they are given a higher dose.

Doctors at 13 hospitals in Indonesia, Singapore, Thailand and Vietnam tested the idea on 326 patients with severe flu symptoms.

Doubling the dose did not ease the duration of the illness, diminish virus levels or alter the risk of death compared with the standard dose, they reported in the British Medical Journal (BMJ). But there was no difference in side effects, either.

Tests on the patients showed five strains of influenza. Most had seasonal flu or the 2009 pandemic H1N1 strain, but a small number (5.2 percent) had H5N1 "bird" flu, a highly dangerous type that causes death in nearly 60 percent of diagnosed cases.

None had the H7N9 flu that has emerged this year in China. A total of 130 people have been infected and 37 died since the H7N9 outbreak started in February.

Tamiflu belongs to a small class of drugs called neuraminidase inhibitors, designed to inhibit the flu virus' reproduction.

"The findings could help to preserve oseltamivir stocks during a future pandemic... if clinicians were to prescribe only regular rather than double doses," Ian Barr and Aeron Hurt, a pair of influenza specialists at the World Health Organisation (WHO), said in a commentary.