Chloroquine is effective against influenza A virus in vitro but not in vivo

BACKGROUND Chloroquine is an inexpensive and widely available 9-aminoquinolone used in the management of malaria. Recently, in vitro assays suggest that chloroquine may have utility in the treatment of several viral infections including influenza. OBJECTIVES We sought to test whether chloroquine is effective against influenza in vivo in relevant animal models. METHODS The effectiveness of chloroquine at preventing or ameliorating influenza following viral challenge was assessed in established mouse and ferret disease models. RESULTS Although active against influenza viruses in vitro, chloroquine did not prevent the weight loss associated with influenza virus infection in mice after challenge with viruses expressing an H1 or H3 hemagglutinin protein. Similarly, clinical signs and viral replication in the nose of ferrets were not altered by treatment. CONCLUSIONS Although in vitro results were promising, chloroquine was not effective as preventive therapy in vivo in standard mouse and ferret models of influenza virus infection. This dampens enthusiasm for the potential utility of the drug for humans with influenza.