Trisodium phosphonoformate selectively inhibits cell-free DNA polymerase activity induced by herpesvirus. The new inhibitor has an antiviral effect on herpes simplex virus types 1 and 2, pseudorables virus, and infectious bovine rhinotracheitis virus in cell culture. It has a good therapeutic activity against cutaneous herpes simplex virus infection in guinea pigs.

Analogues of pyrophosphate have been tested as inhibitors of influenza virus-RNA polymerase activity in cell-free assays. The most active compound, phosphonoformic acid (PFA), reduced the polymerase activity to 50 per cent at a concentration of 20 muM. The inhibition was dependent on the type of divalent cation present in the assay. PFA at a concentration of 400 muM also inhibited the influenza virus plaque formation by 90 per cent.