Broad-spectrum antibiotics as Zithromax can sometimes cause inflammation of the bowel. Zithromax can treat sexually transmitted vaginal or urinary tract is more probably to cause stomach and bowel side effects than the smaller doses prescribed for a skin or respiratory tract infection. The full dosage schedule the effectiveness may be decreased and the bacteria may become resistant to Zithromax and other similar antibiotics. Azithromycin may be used to treat the sexually-transmitted infection chlamydia.