I have a sinus infection about once a year and my doctor prescribes a Zpack which works very well. It also helps me to have 'normal' BMs. I told my doctor this a couple of years ago and he put me on a low dose of erythromicin (sp?) , which did nothing. I think maybe it's the dose of the Zpack or something. I know I couldn't stay on antibiotics forever but why this seems to work so well is a mystery to me.