Misuse of Tamiflu can create resistant influenza viruses (10/4/2007)

Swedish researchers have discovered that oseltamivir (Tamiflu), an antiviral drug used to prevent and mitigate influenza infections is not removed or degraded during normal sewage treatment. Consequently, in countries where Tamiflu is used at a high frequency, there is a risk that its concentration in natural waters can reach levels where influenza viruses in nature will develop resistance to it.

Widespread resistance of viruses in nature to Tamiflu increases the risk that influenza viruses infecting humans will become resistant to one of the few medicines currently available for treating influenza.

"Antiviral medicines such as Tamiflu must be used with care and only when the medical situation justifies it," advises Björn Olsen, Professor of Infectious Diseases with the Uppsala University and the University of Kalmar. "Otherwise there is a risk that they will be ineffective when most needed, such as during the next influenza pandemic."

The Swedish research group demonstrated that oseltamivir, the active substance in Tamiflu, passes virtually unchanged through sewage treatment.

"That this substance is so difficult to break down means that it goes right through sewage treatment and out into surrounding waters," says Jerker Fick, Doctor in Chemistry at Umeå University and the leader of this study.

The Swedish research group also revealed that the level of oseltamivir discharged through sewage outlets in certain countries may be so high that influenza viruses in nature can potentially develop resistance to the drug.

"Use of Tamiflu is low in most countries, but there are some exceptions such as Japan, where a third of all influenza patients are treated with Tamiflu," explains Jerker Fick.

Influenza viruses are common among waterfowl, especially dabbling ducks such as mallards. These ducks often forage for food in water near sewage outlets. Here they can potentially encounter oseltamivir in concentrations high enough to develop resistance in the viruses they carry.

"The biggest threat is that resistance will become common among low pathogenic influenza viruses carried by wild ducks." adds Björn Olsen. "These viruses could then recombinate with viruses that make humans sick to create new viruses that are resistant to the antiviral drugs currently available.

The Swedish researchers advise that this problem must be taken seriously so that humanity's future health will not be endangered by too frequent and unnecessary prescription of the drug today.

Note: This story has been adapted from a news release issued by Umeå University

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