Omaciclovir (previously known as H2G), a cyclic guanosine analog that is structurally similar to acyclovir and was in clinical development for the treatment of herpesvirus infections. This drug acted against varicella-zoster virus (VZV), by the formation of high concentrations of relatively stable H2G-triphosphate, which is a potent inhibitor of the viral DNA polymerases. However, further development of this drug was discontinued.

Torcitabine is the beta-L-enantiomer of the natural nucleoside D-cytidine. The drug was under development as an antiviral agent for the treatment of chronic hepatitis B virus infection. Torcitabine has poor oral bioavailability, but its 3’,5’-derivative ester (val-L-dC) and the 3’-monovaline ester, valtorcitabine dihydrochloride, have excellent oral bioavailability and consequently the torcitabine prodrug, valtorcitabine, has replaced torcitabine in clinical development. Torcitabine is active against hepadnaviruses, specifically human hepatitis B virus (HBV), duck hepatitis virus (DHBV) and woodchuck hepatitis virus (WHV). Torcitabine triphosphate is a selective inhibitor of the polymerase enzyme of HBV.

Fosfonet sodium (or phosphonoacetate sodium), an organophosphorus compound, was found to be a specific inhibitor of the virus-induced DNA polymerases and thus could inhibit specifically the replication of herpes-viruses.

Fosfonet sodium (or phosphonoacetate sodium), an organophosphorus compound, was found to be a specific inhibitor of the virus-induced DNA polymerases and thus could inhibit specifically the replication of herpes-viruses.

Clevudine (also known as L-FMAU) is a nucleos(t)ide reverse transcriptase inhibitor, which inhibits the DNA synthesis activity of the hepatitis B virus polymerase. The drug was approved in Korea and Philippines and is being marketed under the names Levovir and Revovir. The drug is indicated in patients with chronic hepatitis B virus infection. Upon administration, clevudine is metabolized to the active metabolite, clevudine triphosphate, which is responsible for the inhibition of viral polymerase.