(A) Time course design. MDCK cells were infected with H1N1 (A/PR/8/34) at 100 TCID50. The virus absorption was indicated as −1 h and M090 was added at −3 to −1, −1 to 0, −1 to 2, 0 to 2, 2 to 4, 4 to 6, 6 to 8, 8 to 10 h post-infection. After each treatment period, M090 was removed and cells were incubated with culture medium till the end point. (B) M090 was added at each interval, and the virus yield was determined by measuring the TCID50. *p<0.05, ** p<0.01, compared to the condition without drug treatment.