Sorivudine
Sorivudine is a synthetic thymidine analogue with potent antiviral activity against herpes simplex and varicella zoster viruses. Sorivudine is phosphorylated into triphosphate form within the cells; this metabolite interferes with viral DNA replication by inhibiting DNA polymerase activity without been incorporated into elongating viral DNA. Due to the dangerous effects of drug-drug interactions via its metabolite, sorivudine has been removed from the market.