Dosing:   Topical. Apply to cold sore lesions 5 times per day for 4 days, starting within 2 hours of the first sign or symptom.  Must be taken at the first sign or symptom of a cold sore before visible symptoms, for the drug to work.  Preferably should be taken in the first hours after a tingle.

Efficacy:
       Duration: Reduces duration of outbreaks by about half a day, from about 5 days to about 4.5 days.

 

       Severity of outbreaks: Does not reduce severity of an outbreak.
 

       Prevention: ZOVIRAX is not approved for prevention of outbreaks.
 

      

Mechanism of Action: Inhibits DNA replication of herpes viruses.  Acyclovir is phoshporaylated by the herpes virus thymidine kinase (TK).  The phosphorylated acyclovir then inhibits the herpes virus DNA polymerase. 

 

Side Effects: Dryness at the application site.

 

References:

ZOVIRAX cream prescribing information:

www.accessdata.fda.gov/drugsatfda_docs/label/2014/021478s007lbl.pdf