LAUSR

It is need for development of new means against influenza virus due to the lack of efficacy of available therapeutic strategies. In previous research, 1,8‐cineol exert its inhibition of nuclear factor (NF)‐κB, the main regulator of cytokine and chemokine production in influenza, and anti‐inflammatory activity. These fact supports and helps establish the hypothesis that 1,8‐cineol may have synergism with an antiviral on influenza virus infection. The combined effect of 1,8‐cineol with oseltamivir in a mouse type A influenza virus (Victoria/3/75,H3N2) model were examined. We initially tested combinations of 1,8‐cineol (30, 60, and 120 mg/kg/day) and oseltamivir (0.1, 0.2, and 0.4 mg/kg/day). In addition, the 0.4 mg/kg/day of oseltamivir combined with 120 mg/kg of 1,8‐cineol was selected for further combination studies. Oseltamivir was 30%, 40%, and 60% protective at 0.1, 0.2, and 0.4 mg/kg/d. Combinations of 1,8‐cineol (30, 60, and 120 mg/kg/d) and oseltamivir (0.1, 0.2, and 0.4 mg/kg/d) increased the number of survivors and mean survival time (MST) following combination treatment was greater than monotherapy alone. Three dimensional analysis of drug interactions using the MacSynergy method showed a strong synergistic effect of these drug combinations. Survival, MST, lung parameters (lung index, viral titers, and pathology), and cytokines (IL‐10, TNF‐α, IL‐1β, and IFN‐γ) expression in lung demonstrated the high effectiveness of the combination. Combined treatment was associated with longer MST and more reduced cytokine levels than oseltamivir alone. These data demonstrate that combinations of 1,8‐cineol and oseltamivir have synergistic effect against influenza A virus (H3N2) infection.