What Is Azithromycin/Zithromax? Zithromax is a prescription drug that belongs to a group of medicines called macrolide antibiotics. These medicines stop bacteria from growing and making more copies of themselves. Like erythromycin and clarithromycin, Zithromax works by binding to the 50S ribosomal subunit of bacteria. This makes it hard for the bacteria to make proteins, grow, and stay alive. A group of Croatian researchers at Pliva found azithromycin in 1980. It wasn't sold until 1988 in Central and Eastern Europe under the brand name Sumamed. In 1991, the FDA approved azithromycin, and Pfizer put it on the market in the US under the brand name Zithromax. What Does Zithromax Treat? Zithromax can be given to both adults and children, and it is often used to treat infections in the bronchitis, pneumonia, ears, sinuses, and reproductive system that are caused by different types of bacteria. Zithromax is also used to treat sexually transmitted diseases like gonorrhea and chlamydiosis, as well as acne caused by bacteria that is moderate to severe. It is used to treat pneumonia, tonsillitis, middle ear infections, and strep throat in children. Zithromax is not a good choice for treating viral illnesses like the common cold or the flu. Side Effects of Zithromax The most common side effects of macrolide antibiotics are stomach problems like nausea, vomiting, loose stools, and diarrhea. Most of the time, they are small and go away during or after treatment. You can avoid these side effects by eating something before taking the medicine.