While George Abercrombie is flying around the country, trying to convince local governments and large companies to stock up on Roche’s Tamiflu, Swedish researchers are warning the med may be less effective against an influenza pandemic than previously thought.

That’s because the med’s active ingredient, oseltamivir carboxylate, is excreted in the urine and feces. Scientists at Sweden’s Umea University found the drug isn’t removed or degraded in normal sewage treatment. This means Tamiflu’s presence in waterways may allow flu-carrying birds to ingest it and incubate resistant viruses, Bloomberg News reports.

“That this substance is so difficult to break down means that it goes right through sewage treatment and out into surrounding waters,” Jerker Fick, a chemist at Umea University and leader of the study, said in a statement yesterday distributed by EurekAlert, a Web-based science news service. Back in January, researchers from the UK’s Centre for Ecology and Hydrology noted that as much as 80 percent of the Tamiflu taken in each dose is excreted in its active form in urine and feces and the drug could potentially be “maintained in rivers receiving treated wastewater.”

But scientists note that waterfowl, including ducks, are the natural hosts of avian flu. And these birds often forage for food in water near sewage outlets. So it’s possible they might encounter oseltamivir in concentrations high enough to develop resistance in the viruses they carry, according to the Swedish scientists. Their study will to be published in the journal PLoS ONE.

“The biggest threat is that resistance will become common among low pathogenic influenza viruses carried by wild ducks,” said Bjorn Olsen, an infectious diseases professor at Uppsala University and the University of Kalmar. These viruses could then recombine with others that make humans sick to create new ones resistant to the drugs currently available. “Antiviral medicines such as Tamiflu must be used with care and only when the medical situation justifies it. Otherwise there is a risk that they will be ineffective when most needed.”

Strains either resistant or less sensitive to Tamiflu have been linked to the deaths of at least five people in Vietnam and Egypt. A separate study found Tamiflu may be becoming a weaker weapon against the H5N1 avian flu strain in Indonesia, where the virus has killed the most people. Millions of doses of Tamiflu have been stockpiled by governments and WHO to treat and prevent flu infections caused by a pandemic. WHO recommends that people infected by avian flu who are older than 1 year receive a five-day course of 750 milligrams of the medicine.