I have taken many zpaks before because of repetitive sinus infections or strep throat. Had my tonsils removed 3 years ago and got bronchitis recently and was on a 3 day 500 mg per day dose of it and felt fine the first 2 days and just got hit with MAJOR diarrhea....felt like I lost 10lbs in bathroom for 15 mins. YUCK! Hopefully its flushing the sickness from me.