In vitro activity: Vidarabine and Acyclovir have a synergistic effect on wild type . Vidarabine is capable of inhibiting acyclovir-resistant/TK-deficient mutants of HSV and VZV, because it is phosphorylated to its active vidarabine–triphosphate form by cellular kinases and is not dependent for its activation on the viral TK. Vidarabine and acyclovir (ACV) alone show a concentration-dependent inhibition of plaque formation of HSV-1 in Vero cells. Vidarabine combined with acidic protein bound polysaccharide (APBP) show synergistic effects on the plaque formation of HSV-1 in Vero cells. Vidarabine acts directly on the DNA polymerase of varicella-zoster virus (VZV) and double-strand DNA viruses, including human adenoviruses. Vidarabine specifically inhibits adenovirus type 11 replication without obvious cytotoxicity in vitro. Vidarabine acts less on the synthesis of early proteins but rather on those after DNA replication. Vidarabine is an antiviral drug with activity against herpes viruses, poxviruses, and certain rhabdoviruses, hepadnarviruses, and RNA tumor viruses. Vidarabine also is active against vaccinia virus both in vitro and in vivo.

Antiviral Res. 2006 Nov;72(2):157-61; Antivir Chem Chemother. 2004 Sep;15(5):281-5.