It has been about 5-6 weeks since I went back to the 150 mg from the 100 mg. I was on an antibiotic right around Christmas for a sinus infection and I think it made the small amount of rash that had begun to appear on my head again, disappear. Now that I'm done with the antibiotic, it is coming back pretty bad again. My Dr said it is OK to skip a day or 2 of the Tarceva, but I have done that and it didn't seem to help much.