Azithromycin prevents bacterial cells from manufacturing specific proteins necessary for their survival. It differs from other macrolides in its azalide structure. The azalide structure has a methylated nitrogen atom in the number 9a position on the macrolide lactone ring. Azithromycin is sequestered in leukocytes and therefore available at the site of infection in higher concentrations than serum levels. Studies have shown azithromycin to be as effective as amoxicillin/clavulanate in treating acute otitis media.

Azithromycin, as the dihydrate, is a white crystalline powder with a molecular formula of C38H72N2O12•2H2O and a molecular weight of 785.0. It is s macrolide antibiotic related to erythromycin. Azithromycin is an azalide, a subclass member of the macrolide class of antibiotics that is a derivative of erythromycin. Following oral administration azithromycin is rapidly adsorbed and distributed throughout the body. The mechanism of action of this antibiotic includes binding to the 50S large subunit of bacterial ribosomes, thus interfering with protein synthesis. The antibiotic can kill stationary phase P. aeruginosa in culture but only had a minimal effect on bacterial density in the study's subjects. The drug also may work to reduce the inflammatory response. Azithromycin may decrease the viscosity of the patient's sputum, allowing easier clearance of bacteria-laden mucus from the lungs. The drug is an azalide antibiotic. It is more active against gram-negative organisms. It is aborbed from the GIT after oral administration. The blood concentration is low, while the anti-microbial activity is high. It is concentrated in leukocytes and penetrates the tissues well and has a long half life.

Azithromycin is an antibiotic used in combination with other drugs as preventive to treat various bacterial infections, particularly of the sinuses, throat, and respiratory tract (such as bronchitis and pneumonia); infections of the ear; venereal disease due to chlamydial and chancroid infection; skin infections; and diarrhea associated with campylobacter and other bacteria that cause food poisoning. Also used to prevent and treat a tuberculosis-like disease known as Mycobacterium avium complex (MAC), which is common in people with advanced AIDS. Azithromycin is also used for treating cryptosporidiosis. There is no standard treatment for MAC. Recent Public Health Service recommendations suggest either clarithromycin or azithromycin as the first line treatment for MAC, along with at least one other drug, usually ethambutol and one of the following: ciprofloxacin or rifabutin.