— In a flu pandemic, millions of people are expected to take the antiviral drug Tamiflu, but new research shows that ultimately much of the drug will pass through the people taking it and end up in waterways. Chances are it will then linger long enough to promote Tamiflu-resistant flu viruses in wild birds.
As a vaccine tailored to the particular pandemic flu strain is unlikely to be widely available in the early days of an outbreak, emergency plans specify that sick people and, in some cases, people who have been exposed to the virus should be treated with Tamiflu.
A dozen countries have stockpiled more than three billion capsules of the drug. Andrew Singer and colleagues at the Centre for Ecology and Hydrology in Oxford, UK, estimated how much of this could potentially be flushed into lakes and rivers.
The team used detailed sewage runoff models of 16 river catchment areas in the US and UK, and also a model of the expected number of cases of flu per day in a pandemic (see Only drugs and vaccines will deflect bird flu pandemic).
Previous studies have shown that Tamiflu is unusually resistant to being broken down in the body about 80% of it is excreted in its active form. The drug also dissolves readily in water, and is not broken down in sewage sludge or by common chemical reactions in nature.
Putting all this together, the researchers found that all the UK catchments, and most in the US, developed high enough concentrations of the drug to stop a flu virus from replicating, for weeks or months.
Avian flu viruses normally live in the guts of birds. In ducks that drink Tamiflu-contaminated water, the drug concentration that the team predicted would prevent susceptible viruses from replicating, giving drug-resistant viruses a selective advantage.
Such viruses may not make much difference to ducks. But flu viruses regularly swap genes, so Tamiflu resistance could end up spreading to human strains of flu, they warn.
We recommend more research to study how Tamiflu behaves in water, and to determine cheap and easy ways to break it down before it reaches the river, says Singer, who led the research. The team suggests that perhaps some chemical that destroys Tamiflu might be put down the toilet by people taking the drug.
Journal reference: Environmental Health Perspectives (DOI: 10.1289/ehp.9574)
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