Azithromycin Antibiotic Classification
Azithromycin is classified as an azalide, which is a subclass of macrolide antibiotics. 1, 2
Structural Classification
- Azithromycin is structurally derived from erythromycin but differs by having a methyl-substituted nitrogen atom incorporated into the lactone ring, which expands it from a 14-membered to a 15-membered ring structure 1, 2
- This structural modification distinguishes azalides as a distinct subclass within the broader macrolide family 3
- The chemical alteration results in the molecular formula C38H72N2O12 with a molecular weight of 749 1
Relationship to Macrolides
- While azithromycin is the sole member of the azalide subclass, it shares the fundamental macrolide mechanism of action by binding to the 50S subunit of bacterial ribosomes to inhibit protein synthesis 4, 5
- Azithromycin is grouped with other macrolides (erythromycin, clarithromycin) in clinical guidelines for treatment recommendations, reflecting their similar antimicrobial spectrum and clinical applications 4
- The British Thoracic Society and other guideline organizations classify azithromycin alongside clarithromycin and erythromycin as macrolide/azalide antibiotics when discussing treatment options 4
Pharmacodynamic Classification
- Azithromycin exhibits time-dependent killing with moderate to prolonged persistent effects, similar to other macrolides 4
- The pharmacodynamic parameter correlating with efficacy is the AUC to MIC ratio (approximately 25 for maximal efficacy) rather than time above MIC, due to its prolonged postantibiotic effect 4
Clinical Context
- In antimicrobial treatment guidelines, azithromycin is consistently categorized within the macrolide class for empiric therapy decisions in respiratory tract infections, sexually transmitted diseases, and other bacterial infections 4
- The CDC and other guideline bodies refer to azithromycin as a macrolide agent when making treatment recommendations for pertussis and other infections 4