AIM: Favipiravir and oseltamivir are antiviral compounds used for the treatment 
of influenza infections. We have aimed to investigate the efficacy of the 
compounds in combination to treat influenza H1N1 virus infections in mice.
MATERIALS & METHODS: Mice infected with pandemic influenza A/California/04/2009 
(H1N1pdm) virus or an oseltamivir-resistant (H275Y neuraminidase mutation) 
influenza A/Mississippi/ 3/2001 (H1N1) virus were treated orally with inhibitors 
twice a day for 5 days starting 4 h after infection.
RESULTS: Complete protection from death was afforded by favipiravir treatments 
of 100 mg/kg/day, but lower doses were less effective. Combinations of 
oseltamivir (1 and 3 mg/kg/day) with favipiravir (3, 10 and 30 mg/kg/day) 
resulted in a synergistic improvement in survival rates against H1N1pdm 
infections. Significant reductions in lung virus titers also occurred. Against 
the H275Y virus infection, oseltamivir alone was only 30% protective from death 
at 100 mg/kg/day, but combinations of the two compounds produced a synergistic 
improvement in survival rate.
CONCLUSION: The utility of treating H1N1 influenza virus infections with 
oseltamivir and favipiravir in combination has been established.