Oral acyclovir in prevention of herpes labialis. A randomized, double-blind, multi-centered clinical trial

Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 1998 Jan;85(1):55-9. doi: 10.1016/s1079-2104(98)90398-5.


Objective: A three-center, randomized, double-blind, placebo-controlled acyclovir clinical trial was conducted among Canadian skiers over a 2-year period.

Study design: All patients enrolled in the study reported a history of recurrent herpes labialis with a greater-than-50% chance of a sun-induced trigger. There were 239 patients enrolled, and 237 of these were included in the analysis. For a minimum of 3 days and a maximum of 7 days, each patient received 800 mg of oral acyclovir twice daily (1600 mg/day) 12 to 24 hours before exposure to the sun. A minimum of 3 hours of outdoor activity was required each day.

Results: No differences were detected in baseline and outcome measures among the centers, and results from all three centers were combined for further analysis. There was no difference in healing rate between the acyclovir and placebo groups for the first 4 days. Patients using acyclovir healed slightly faster on days 5 and 6, and nearly all patients in both the acyclovir and placebo groups were healed by day 7. Adverse events were evenly distributed; no withdrawals were required in either group.

Conclusion: 800-mg oral acyclovir taken twice a day was not significantly better than a placebo either in effectiveness and prevention of recurrent herpes labialis or in adverse effects.

Publication types

  • Clinical Trial
  • Multicenter Study
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acyclovir / therapeutic use*
  • Adult
  • Antiviral Agents / therapeutic use*
  • Chi-Square Distribution
  • Double-Blind Method
  • Female
  • Herpes Labialis / prevention & control*
  • Humans
  • Male
  • Recurrence
  • Statistics, Nonparametric


  • Antiviral Agents
  • Acyclovir