U.S. utilization patterns of influenza antiviral medications during the 2009 H1N1 influenza pandemic

The 2009 H1N1 influenza pandemic in the United States occurred from April 2009 to April 2010. The 2009 H1N1 influenza virus was susceptible to neuraminidase inhibitors (oseltamivir and zanamivir).

To characterize the 2009 H1N1 influenza pandemic in the United States from April 2009 to April 2010 using weekly influenza antiviral prescription utilization data and the CDC's weekly reports of the number of visits for influenza-like-illnesses by the Influenza Sentinel Provider Surveillance Network.

A proprietary outpatient data source used by the FDA, which captures adjudicated U.S. prescription claims for select influenza antiviral drugs, was used to conduct this analysis. Data were extracted weekly and analyzed for surveillance during the pandemic. Results were compiled at the end of the pandemic.

Oseltamivir has dominated the U.S. influenza antiviral market share of dispensed prescriptions since approval in October 1999 and was the primary influenza antiviral drug used during the 2009 H1N1 influenza pandemic. However, commercial availability of the suspension formulation of oseltamivir was reduced by high demand during the pandemic. Dispensed prescription trends of other influenza antiviral medications studied followed that those of oseltamivir, even antivirals for which the 2009 H1N1 strains showed resistance.

Weekly prescription utilization of all influenza antivirals used to treat influenza during the seasonal influenza outbreak followed the same trend of weekly reports of the number of visits for influenza-like-illnesses (ILI) by the Influenza Sentinel Provider Surveillance Network. The ILI epidemic curve resembled dispensed antiviral prescription trends (both overall and stratified by age), providing some corroboration for the surveillance data.