Antiviral activity of FA-11H on the infectivity and replication of herpes simplex virus type 1 in cultured cells.

The highest concentration lacking cytotoxicity (h.c.l.c.) of the acid FA-11H, related to ester FA-11 (ethyl 4-trifluoromethyl-2-methylthio-5-pyrimidinecarboxylate), was determined on Vero cultured cells. At this concentration (300 micrograms/ml) FA-11H produced an 81.4% inhibition of herpes simplex virus type 1 infectivity with respect to the plaque formation detected in control infected cultures. This inhibitory activity was substantiated by studies on progeny production. FA-11H revealed a higher therapeutic index than that of the related ester FA-11. However, the therapeutic index of FA-11H appeared to be lower than that of its potassium salt. These results indicate that the presence of potassium ions could facilitate the internalization and therefore the antiviral activity of the anions corresponding to analysed compound.