Amoxicillin (CAS 26787-78-0) is a broad-spectrum, semi-synthetic penicillin antibiotic with the chemical formula C₁₆H₁₉N₃O₅S and molecular weight 365.40 g/mol. It is a white to off-white crystalline powder, slightly soluble in water. In analytical and microbiology laboratories, it serves as a reference standard for HPLC purity assays, identification, and antimicrobial susceptibility testing. Clinically, it is widely used to treat various bacterial infections, including respiratory tract infections such as pneumonia and bronchitis, ear, nose, and throat infections like sinusitis and otitis media. It is also prescribed for urinary tract infections, skin infections, and certain gastrointestinal infections caused by Helicobacter pylori, often in combination with other medications. Additionally, it is used in dental procedures to prevent infections and in some cases to treat Lyme disease. Its broad-spectrum activity makes it a common choice for both adults and children.