Azithromycin may be used to treat the sexually-transmitted infection chlamydia. Zithromax should be taken on an empty stomach two hours after a meal since food reduces its absorption. 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. If you regularly take antiretroviral drugs you should tell your doctor if you experience any new side effects while taking a course of Azithromycin.