Azithromycin is a semisynthetic macrolide antibiotic derived from erythromycin, belonging to the azalide subclass. Its chemical formula is C₃₈H₇₂N₂O₁₂, with a molecular weight of 749.00. As a reagent, it is typically supplied as a powder with 98% purity by HPLC for use in pharmaceutical research, microbiological testing, antibiotic susceptibility assays, and as a reference standard. Clinically, it is used to treat a wide range of bacterial infections, including respiratory tract infections, skin infections, ear infections, and sexually transmitted infections like chlamydia. It is effective against certain Gram-positive and Gram-negative bacteria, as well as some atypical pathogens such as Mycoplasma and Chlamydia species. Commonly prescribed for bronchitis, pneumonia, sinusitis, and strep throat when caused by susceptible bacteria. Often chosen for its once-daily dosing and shorter treatment duration compared to other antibiotics. Also used in prophylaxis for certain infections in immunocompromised patients. Available in oral, intravenous, and suspension forms, making it suitable for adults and children.