N-Demethylazithromycin is a major metabolite of the macrolide antibiotic azithromycin. It is primarily used in research settings to study antibiotic metabolism, including demethylation pathways, and resistance mechanisms in bacteria. Due to its close structural similarity to azithromycin, it facilitates comparative pharmacokinetic and pharmacodynamic studies. It also serves as a reference standard in bioanalytical assays, such as HPLC or LC-MS, for quantifying azithromycin metabolites in plasma, urine, or other biological fluids, aiding in the evaluation of drug efficacy, safety, and therapeutic drug monitoring.