Extended use of antiviral drugs found to be safe and effective in preventing symptomatic influenza
Two drugs used to combat the effects of the influenza virus are both safe and efficacious, a new study finds. The drugs (oseltamivir and zanamivir) keep the virus from spreading within the body by inhibiting the enzyme neuraminidase. The virus uses this enzyme to break out of infected cells after multiplying within them, explains Nayer Khazeni, M.D., M.S., of Stanford University Medical Center. She and colleagues conducted a systematic review of studies of the safety and efficacy of the two neuraminidase inhibitors (NAIs). They combined results from seven placebo-controlled, double-blind studies (neither participant nor investigator know what drug/placebo is given) involving 7,021 participants who received one of the NAIs or a placebo for longer than 4 weeks.
Overall, the drugs reduced the relative frequency of symptomatic influenza by three-fourths, preventing about 1 case in every 25 people who received them. The drugs did not prevent asymptomatic influenza virus infection. There was an increased risk for nausea and vomiting with extended use of oseltamivir. However, there was no increase in other adverse events with use of currently recommended prophylactic doses of oseltamivir or zanamivir.
This is important news, given the high prevalence of oseltamivir resistance among currently circulating seasonal influenza A virus strains and reports of oseltamivir-resistant influenza A (H5N1) virus strains. In fact, the governments of the United States, the United Kingdom, and Canada recently announced plans to add millions of doses of zanamivir to their antiviral stockpiles. Because the original studies included only persons with competent immune systems of white or Japanese descent, future studies should include participants from other racial or ethnic groups, the researchers suggest. Their study was funded in part by the Agency for Healthcare Research and Quality (HS18003).
More details are in "Systematic review: Safety and efficacy of extended duration antiviral chemoprophylaxis against pandemic and seasonal influenza," by Dr. Khazeni, Dena M. Bravata, M.D., M.S., Jon-Erik C. Holty, M.D., M.S., and others in the Annals of Internal Medicine 151(7), pp. 464-473, 2009.
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