RESUMO
In April 2009, the first swine origin pandemic influenza (H1N1 2009) infection was reported in Mexico and United states and has since spread rapidly worldwide. Finally on June 11, 2009, WHO officially declared the first pandemic of the 21st century. Until March 2010, more than 213 countries reported laboratory confirmed cases of pandemic influenza H1N1 2009, including at least 16,931 deaths. The drug of choice for treatment and prophylaxis of pandemic (H1N1) 2009 influenza are the neuraminidase inhibitor (oseltamivir and Zanamivir). However, increased use of these drugs lead to the emergence of oseltamivir-resistant strains. We report a case of oseltamivir-resistant pandemic influenza (H1N1 2009) virus infection in a patient who were initially started with oseltamivir for laboratory-confirmed influenza. Patient's symptoms worsened despite the use of high-dose oral oseltamivir, and antiviral susceptibility test showed oseltamivir resistance (H275Y mutation). The patient resolved after treatment with zanamivir.