Foscarnet decreases serum and liver duck hepatitis B virus DNA in chronically infected ducks.

Foscarnet (trisodium phosphonoformate) is a new antiviral compound with in vitro inhibitory effects against the DNA polymerases of hepadna viruses. To study the effects of the drug in chronic hepadna virus infection, we treated ducks chronically infected with duck hepatitis B virus for 10 days with either low-dose foscarnet (50 mg/kg i.p. b.i.d.), high-dose foscarnet (250 mg/kg i.p. b.i.d.), or sterile water injections. Serum duck hepatitis B virus DNA and intrahepatic replicative forms of the virus were measured using molecular biological techniques with both a double-stranded radiolabeled DNA probe and a plus-strand (noncoding) specific RNA probe. We found a dose-related decrease in serum and intrahepatic duck hepatitis B virus DNA during treatment, with a rapid return toward baseline values after the cessation of treatment. There was a disproportionate decrease in the plus strand of viral DNA with treatment. We conclude that foscarnet exerts its effect in hepadna virus infection through inhibition of viral DNA polymerase. Further study is necessary to determine whether foscarnet, by itself or in combination with other treatment modalities, has a role to play in the treatment of chronic hepatitis B infections in humans.