Antibiotics as Zithromax can sometimes cause inflammation of the bowel. Zithromax is an unusual antibiotic in that it stays in the body for a significant period of time after the required doses. The unusual bit of facts about this drug is that it is found to be present in the body for quite a long time as it has a prolonged half-life that allows for once a day dosing and also for short-term treatment courses for most infections.