No in vivo effect of trisodium phosphonoformate on woodchuck hepatitis virus production

The efficient in vitro inhibition of hepatitis B virus DNA polymerase by trisodium phosphonoformate (PFA, INN: foscarnet sodium) and its low toxicity suggested that PFA could be used as a therapeutic agent for hepatitis B infection. PFA was also found to inhibit woodchuck hepatitis virus (WHV) DNA polymerase in vitro. As a model to test PFA's eventual effect, chronically WHV infected woodchucks were treated with PFA. The animals were treated twice daily in a dosage which gave a minimum serum level of PFA corresponding to an in vitro inhibiting effect on WHV DNA polymerase of about 40%. The concentration in liver tissue was found to be 15% below serum level. The amount of WHV particles in serum was followed by DNA polymerase assay. No effect on WHV production could be seen during 2 weeks' treatment. No change of the in vitro sensitivity to PFA of the WHV DNA polymerase was seen. These results indicate that the WHV associated DNA polymerase has no role in the production of viral particles.