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Oseltamivir resistance increased among influenza A H1N1 viruses
The CDC plans to issue new guidelines for influenza antiviral use before the 2009/2010 influenza season.
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Oseltamivir resistance among the influenza A H1N1 strains continues to rise, and the Advisory Committee on Immunization Practices influenza working group is encouraging physicians to consult local influenza surveillance data and utilize diagnostic testing to make the best antiviral choices.
“Oseltamivir (Tamiflu, Roche)-resistant H1N1 is the most commonly isolated virus thus far this season,” Anthony Fiore, MD, MPH, CDC liaison to the influenza working group said at the meeting. “Clinicians need to know that oseltamivir alone may not effectively prevent or treat influenza.”
To date, 264 of the tested 268 influenza A H1N1 viruses from the 2008/2009 season were resistant to oseltamivir. Currently, rapid tests to identify influenza A subtypes and antiviral resistance do not exist.
“Treatment with zanamivir or a combination of oseltamivir and rimantadine or amantadine is preferable in situations where the influenza subtype is likely to be H1 or unknown,” Fiore said.
WHO officials suggest that increased resistance is not associated with usage, as no correlation between oseltamivir usage and prevalence of resistance has been detected thus far and most patients with H1N1 infections have had no previous exposure to the antiviral.
The influenza working group plans to present draft recommendations for antiviral treatment and chemoprophylaxis at the next ACIP meeting in June, and new CDC recommendations are expected to be published before the 2009/2010 influenza season. – by Nicole Blazek
The National Institutes of Allergy and Infectious Diseases Collaborative Antiviral Study Group had a meeting last week on antiviral resistance, and I think the summary of it is that virologists don’t fully understand the emergence of oseltamivir resistance on such a widespread scale. It truly does not seem related to use of oseltamivir, as resistance is appearing in countries that have had very low utilization of oseltamivir. Although there may be a rationale for duel therapy using oseltamivir and either rimantadine or amantadine, we definitely need more safety and pharmacokinetic information, if not for efficacy at least for safety and knowledge that these classes of drugs can be used together safely without any kind of antagonism. Secondly, rimantadine and amantadine are in the same situation that zanamivir has posed in which widespread utilization was not anticipated and now we’re facing an increased demand. Many pediatricians are having a difficult time actually getting a hold of those two drugs.
– David W. Kimberlin, MD
Infectious Diseases in Children Editorial Board Member
This news highlights the potential limitations of using antiviral medications. While these agents can be useful in limiting the clinical impact of influenza in some children, recent news of viral resistance to oseltamivir illustrates that prevention of influenza is indeed preferable whenever possible. Children 6 months of age and older should receive influenza immunization unless specific contraindications exist, and it is not too late to administer influenza immunization to children who have not yet received it.
– Edward A. Bell, PharmD
Infectious Diseases in Children Editorial Board Member
For more information:
- Fiore A. Influenza surveillance update. Presented at: the ACIP meeting; Feb. 25-26, 2009; Atlanta.