Effect of caffeine on experimental influenza in mice

Three 50-gamma, 125-gamma or 250-gamma doses of caffeine were administered to mice by intranasal (i.n.) route, either before or after i.n. inoculation of influenza virus A/PR8/34 (H1N1) A decrease in mortality by 30-50%, a slight increase in mean survival time and a significant decrease in the hemagglutinating (HA) titer of the virus were achieved by application of 125-gamma doses prior to virus inoculation. When given after inoculation caffeine appeared to induce only a reduction in HA titers. The HA capacity of an influenza virus suspension was significantly reduced by in vitro contact with caffeine. The possible mechanism underlying the antiinfluenza effect of caffeine is briefly discussed.