Macrolides are a class of antibiotics characterized by their large lactone ring structure, which inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit. They are clinically significant for treating respiratory infections, skin infections, and certain sexually transmitted diseases, particularly in patients allergic to penicillin. A key example is azithromycin, which is associated with potential complications such as QT interval prolongation, leading to arrhythmias.