How to Use Anti-influenza Drugs: Zanamivir and Oseltamivir

Zanamivir and oseltamivir have been used worldwide for the treatment of influenza for about 20 years, zanamivir as an inhaled and oseltamivir as an oral drug, with both administered twice daily for 5 days. For prophylaxis, both are administered once daily for 7–10 days. They are almost equally effective for influenza A. Oseltamivir is less effective against influenza B than against influenza A; however, it is sufficiently effective that it is much better than using no drug at all. The oseltamivir-resistant (H274Y mutated) seasonal H1N1 virus was prevalent in the 2008–2009 season, and the effectiveness of oseltamivir was less than that of zanamivir in that season; however, the oseltamivir-resistant seasonal H1N1 virus disappeared after the emergence of the novel N1N1 pandemic influenza virus (H1N1pdm09) in 2009. Of note, oseltamivir has shown continued effectiveness against H1N1pdm09 since the 2009–2010 season, as effective as against seasonal H1N1 in the 2007–2008 season and before. Zanamivir has been effective for 20 years, and no resistant virus has been found to date.