The synergistic effects of betulin with acyclovir against herpes simplex viruses

Antiviral Res. 2004 Nov;64(2):127-30. doi: 10.1016/j.antiviral.2004.05.006.


Betulin, a pentacyclic triterpenoid, was isolated from the bark of Betula papyrifera. The antiviral efficacies of betulin on herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) were evaluated using viral plaque reduction assays on Vero cells. The results indicate that betulin is active against both HSV-1 and HSV-2 infections with the 50% effective concentrations (EC(50)) of 0.40 and 4.15 microg/ml, respectively. The cytotoxicity of betulin was examined on Vero cells using a neutral red uptake assay. The 50% cytotoxic concentration (CC(50)) of betulin was 73.1 microg/ml. A synergistic antiviral effect between betulin and acyclovir (ACV) was determined by drug combination studies. Strong and moderate synergistic antiviral effects were observed for betulin and ACV against HSV-1 when the concentrations of ACV and betulin were higher than 0.068 and 0.4 microg/ml, respectively. At the concentrations lower than these, additive effect was found. Synergistic antiviral effects were also found against HSV-2 at higher concentrations than for HSV-1, i.e. 0.45 microg/ml of ACV combined with 8.4 microg/ml of betulin.

MeSH terms

  • Acyclovir / pharmacology*
  • Animals
  • Antiviral Agents / pharmacology*
  • Chlorocebus aethiops
  • Drug Synergism
  • Drug Therapy, Combination
  • Herpesvirus 1, Human / drug effects*
  • Herpesvirus 2, Human / drug effects*
  • Humans
  • Triterpenes / pharmacology*
  • Vero Cells
  • Viral Plaque Assay


  • Antiviral Agents
  • Triterpenes
  • betulin
  • Acyclovir