Mutations conferring resistance are single amino acid residue substitutions (His274Tyr) in the neuraminidase enzyme.
Seasonal H1N1
According to the CDC, oseltamivir is not very effective in the 2008 seasonal H1N1 virus anymore due to acquired resistance in 99.6% of all 2008 seasonal H1N1 strains, up from 12% in 2007-2008 flu season.
H3N2
Mutant H3N2 influenza A virus isolates resistant to oseltamivir were found in 18% of a group of 50 Japanese children treated with oseltamivir. Several explanations were proposed by the authors of the studies for the higher-than-expected resistance rate detected. First, children typically have a longer infection period, giving a longer time for resistance to develop. Second, Kiso ''et al.'' claim to have used more rigorous detection techniques than previous studies. According to the CDC, as of October 3, 2009 no influenza B strains tested have shown any resistance to oseltamivir.
H5N1 avian influenza
High-level resistance has been detected in one girl suffering from H5N1 avian influenza in Vietnam. She was being treated with oseltamivir at time of detection. de Jong ''et al.'' (2005) describe resistance development in two more Vietnamese patients suffering from H5N1, and compare their cases with six others. They suggest that the emergence of a resistant strain may be associated with a patient's clinical deterioration. They also note that the recommended dosage of oseltamivir does not always completely suppress viral replication, a situation that could favor the emergence of resistant strains. Moscona (2005) gives a good overview of the resistance issue, and says that personal stockpiles of oseltamivir could lead to under-dosage and thus the emergence of resistant strains of H5N1.
Resistance is of concern in the scenario of an influenza pandemic (Wong and Yuen 2005), and may be more likely to develop in avian influenza than seasonal influenza due to the potentially longer duration of infection by novel viruses. Kiso ''et al.'' suggest that "a higher prevalence of resistant viruses should be expected" during a pandemic.
H5N1 has not yet been transmissible from person to person and is acquired by people working with or near infected poultry.
Further Reading
This article is licensed under the Creative Commons Attribution-ShareAlike License.
It uses material from the Wikipedia article on
"Oseltamivir"
All material adapted used from Wikipedia is available under the terms of the
Creative Commons Attribution-ShareAlike License.
Wikipedia® itself is a registered trademark of the Wikimedia Foundation, Inc.