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Tamiflu, Relenza Safely Prevent Flu Illness

But Child Safety, Rare Side Effects Unknown when Flu Drugs Used for Prevention
WebMD Health News

Aug. 3, 2009 - Tamiflu and Relenza safely prevent flu in adults, but experts were surprised to find no data on the drugs' safety or efficacy when used to prevent flu in kids.

A search of the medical literature by Stanford researcher Nayer Khazeni, MD, and colleagues turned up just seven placebo-controlled clinical trials of how well Tamiflu and Relenza work when used not to treat flu, but to prevent it.

The drugs don't actually keep a person from getting infected with the flu bug. But they keep flu viruses from multiplying in the body. And the studies show that people are far less likely to have flu symptoms while taking either Tamiflu or Relenza.

"Among adults, extended-duration [use of Tamiflu or Relenza for prevention] was efficacious in preventing symptomatic, but not asymptomatic influenza virus infection, with no statistically significant difference in efficacy between [Tamiflu] and [Relenza]," Khazeni and colleagues conclude.

But they note that all of the studies were funded by the drug's manufacturers, and that the authors of six of the seven studies were paid consultants of these companies. Khazeni suspect that there was "publication bias" -- that is, that the most favorable studies were published while less favorable studies may not have been.

"These are still high-quality studies, but we always like to see research that is independently funded, and we don't have that in this case," Khazeni says in a news release.

And there are gaps in what the studies show:

•         Although Tamiflu and Relenza have been used during the H1N1 swine flu pandemic to prevent disease in children, none of the prevention studies included kids under age 12.

•         The study did not include people with immune suppression, even though such people are at high risk of severe complications from flu. However, two of the studies did include some of the groups at risk of severe flu disease and found that these people had the same benefit as low-risk individuals.

•         Each wave of a flu pandemic lasts about eight to 12 weeks. Yet the studies looked only at using Tamiflu or Relenza for four weeks.

•         Whites and Japanese were the only races/ethnicities included in the studies.

•         None of the studies was large enough to detect rare side effects.

Nevertheless, the studies clearly showed that the drugs can protect against flu illness, and that they are safe for adults. The most notable side effect was seen in people taking Tamiflu: They were more likely than those taking a placebo to report nausea and vomiting.

Both Tamiflu and Relenza are safe and effective treatments for H1N1 swine flu. One of the seasonal flu bugs has become resistant to Tamiflu, however, and Relenza -- which must be taken as an inhaled powder -- cannot be given to people with lung disease or to children under age 5.

Khazeni and colleagues report their findings in the Aug. 4 issue of Annals of Internal Medicine.

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