Hi ! I'm sorry to hear about the fever blisters you've been getting. I'm sure you've already seen this, but we have a featured collection about topical chemotherapy that has a lot of helpful information about Efudex and side effects: https://skincancer.net/topical-chemotherapy-guide. Have you started taking the Valtrex yet and, if so, has it helped at all? I hope others are able to chime in with their experience, but I'm so glad to hear you've already been proactive about asking your doctor for help. Efudex can be unpredictable, so it's always best to check in with your doctor when something new pops up. Please keep me posted on how you're doing - I'll be thinking about you! -Alexa (SkinCancer.net moderator)