Hey guys. Really quick question. I did some googling and wasn't able to find one solid answer. I had a little sinus infection about a week and a half ago that the doctor put me on a 5-day Z-Pak for. Cleared it up pretty well. Well then about 3 days after my dosage stopped, my mom started coming down with what turned out to be bronchitis. My question is basically, how long does an antibiotic stay effective in killing things off. She just started taking a course for herself today. It's basically been a little over a week since I stopped my course of them.