Medscape - Infection-specific dosing for Zithromax (azithromycin), frequency-based adverse effects, comprehensive interactions, contraindications, pregnancy & lactation schedules, and cost. Azithromycin is a semi-synthetic antibiotic of the azalide subclass, derived from the classical macrolide erythromycin by the insertion of a methylated nitrogen atom into the 14-membered macrolactone ring, expanding it to a 15-membered ring. Learn about azithromycin (Zithromax) usage and dosing. Read the latest news and reviews about the drug as well as potential side effects and popular alternatives. Overview: Azithromycin is an antibiotic that is used to treat certain bacterial infections. It works by stopping certain types of bacteria from making proteins they need to grow and multiply. Azithromycin (Zithromax) is an antibiotic medication that treats bacterial infections. It doesn’t treat viral infections. It works by killing bacteria or preventing their growth. However, this medicine will not work for colds, flu, or other virus infections. This medicine is available only with your doctor's prescription. This product is available in the following dosage forms: Zithromax is an antibiotic that fights bacteria. Zithromax is used to treat many different types of infections caused by bacteria, such as respiratory infections, skin infections, ear infections, and sexually transmitted diseases. ZITHROMAX 500 mg tablets are supplied as pink modified capsular shaped, engraved, film-coated tablets containing azithromycin dihydrate equivalent to 500 mg of azithromycin. ZITHROMAX 500 mg tablets are engraved with “Pfizer” on one side and “ZTM500” on the other. Azithromycin is used to treat many different types of infections caused by bacteria, such as respiratory infections, skin infections, ear infections, eye infections, and sexually transmitted diseases. Azithromycin may also be used for purposes not listed in this medication guide. In sexually transmitted diseases in men and women, azithromycin is indicated for the treatment of uncomplicated genital infections due to Chlamydia trachomatis. It is also indicated for the treatment of chancroid due to Haemophilus ducreyi and uncomplicated genital infections due to non-multiresistant Neisseria gonorrhoeae; concurrent infection with Treponema pallidum should be excluded.