Clemastanin B has antioxidant and anti-inflammatory activities, it exerts its anti-influenza activity by inhibiting the virus multiplication, prophylaxsis and blocking the virus attachment.

The experiment consisted of four parts: therapeutic action, prophylaxsis action, inhibition of virus attachment, and direct virucidal action. Cytopathic effect (CPE) and 3-(4,5-Dimethylthiazol-2-yI)-2,5-diphenyltetrazolium (MTT) were used to assess antiviral activity. CB, epigoitrin, PEP and PEP ALK OA fractions from Banlangen (Radix Isatidis) extract significantly increased the viability of MDCK cells pre-infected with the virus compared with the virus control group in all the dilutions (P < 0.01). Pretreated with either pure compounds or chemical fractions of Banlangen (Radix Isatidis) extract in all the dilutions significantly improved the viability of MDCK cells (P < 0.01). The inhibition of virus absorption to the host cells by CB, epigoitrin and PEP was in a dose dependent manner.