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. Zithromax is a prescription antibiotic that is now available for buying online. Zithromax is prescribed for adult people to treat certain mild to moderate skin infections. Common side effects are counted as loose stools or diarrhea, abdominal pain, diarrhea or loose stools, nausea, abdominal pain, diarrhea or loose stools, loss of appetite, nausea, abdominal pain, and vomiting which may occur in fewer than one in twenty persons who are treated with Azithromycin.