Tarceva

My husband was diagnosed with stage 4 non small call lung ca in January 07. He is 55 yrs old tested positive for a genetic mutation of the cancer. He has been on Tarceva 150mg at first, had to go down to 100mg becouse of the side effects. Mainly severe diarrhea, rash and fatigue. At present he is doing great and a repeated CT of his chest showed amazing shrinkage of the tumor, and disappearance of the previous bone mets. He feels great, and looks well.This is my question: does anyone have any experience on what is the usual protocol with Tarceva? such as how long to take it, what dose, and most importantly if someone takes this medication for a prolonged period of time, does it lose it efficacy?Also my hubdand has been on monthly injections...