Fidaxomicin is the major analogue of a family of macrocyclic lactones isolated independently by three different groups from cultures belonging to three different genera (Actinoplanes, Dactylosporangium and Micromonospora) known as lipiarmycin A3, tiacumicin B and clostomicin B1, respectively. Fidaxomicin is a narrow spectrum antibiotic with excellent activity against Gram positive bacteria, notably Clostridium difficile. Fidaxomicin acts in the gastrointestinal tract without undue disruption to gut microbial flora.