My family member is having a cold sore outbreak and has been taking max dose of acyvlovir 800mg/5 times day for two days, but is now getting another cold sore. what is best course of action? switch to valacyclovir?

Either acyclovir or Valtrex can reduce the length of time a "cold sore" ulcer is present, and prevent additional ulcer formation, but once an ulcer appears, in an individual who has prior exposure to the herpes virus, the treatment with either acyclovir or Valtrex is equally effective in treating the re-emergence of additional ulcers. Reducing anxiety or stress can also reduce new ulcers forming.

Are you sure of the diagnosis? Oral herpes (cold sore) outbreaks usually are outside of the lips or elsewhere on the face. Sores in the mouth (aphthous stomatitis, canker sores) are not herpes. It is quite unusual improvement within 2-3 days of such treatment. In fact, the recommended treatment of choice is a single dose of valacylovir 2 grams; no need for several days Rx.