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H1N1 Update: Oseltamivir Resistance and Antiviral Use

The CDC reports oseltamivir-resistant 2009 pandemic influenza A (H1N1) virus infection in two children who received prophylaxis and provides revised recommendations for antiviral use during the 2009 flu season.

Although sporadic cases of oseltamivir-resistant 2009 pandemic influenza A (H1N1) virus infection have been reported, oseltamivir remains an important tool in our armamentarium against flu. In July 2009, two girls residing in the same camp cabin in North Carolina developed oseltamivir-resistant 2009 (H1N1) virus infection while receiving oseltamivir as part of a mass prophylaxis program during an influenza outbreak. Both girls recovered fully. Whether the one girl case transmitted the virus to the other or whether both girls were infected by another camper is uncertain. One girl continued to receive prophylactic (not therapeutic) doses of oseltamivir during the first 4 days of her illness, which could have contributed to the development of resistance.

On September 8, 2009, the CDC updated recommendations for use of antiviral medications in the treatment and prevention of influenza for the 2009–2010 influenza season. The new recommendations include the following additions aimed at reducing the likelihood of resistance and ensuring adequate antiviral drug supplies:

• Do not use antivirals for postexposure chemoprophylaxis in healthy children or adults to manage outbreaks in the community, school, camp, or other settings.
  
• Age-based dosing recommendations are provided for children younger than 1 year.
  

For high-risk individuals, consider:

• Increased use of preemptive therapy after exposure with an emphasis on prompt treatment of symptomatic people in lieu of prophylaxis. (Remember that the doses for prophylaxis and therapy are different.)
  
• Establishing systems to ensure rapid access to antiviral therapy when needed (e.g., providing telephone consultation and prescriptions after office hours or giving prescriptions to patients to fill if needed only after speaking with a physician).
  

Comment: Pandemic influenza poses multiple challenges related to the frequency of changes in information and recommendations. These case reports and recommendations highlight the need for judicious use of antivirals in otherwise healthy individuals and rapid access to appropriate therapy in high-risk patients. Antiviral therapy is most effective when started within 48 hours after the onset of symptoms. Vaccination (when available) remains the mainstay of prevention and is far preferable to prophylaxis.

— Peggy Sue Weintrub, MD

Dr. Weintrub is on the Speakers' Bureau for MedImmune (maker of FluMist) and Sanofi-Aventis (makers of standard flu vaccine).

Published in Journal Watch Pediatrics and Adolescent Medicine September 16, 2009

Citation(s):

Centers for Disease Control and Prevention (CDC). Oseltamivir-resistant 2009 pandemic influenza A (H1N1) virus infection in two summer campers receiving prophylaxis — North Carolina, 2009. MMWR Morb Mortal Wkly Rep 2009 Sep 11; 58:969.

• Medline abstract (Free)

Centers for Disease Control and Prevention (CDC). Updated interim recommendations for the use of antiviral medications in the treatment and prevention of influenza for the 2009-2010 season. Sep 8 , 2009. (http://www.cdc.gov/h1n1flu/recommendations.htm)

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