Fidaxomicin (trade names Dificid, Dificlir in Europe) is the first in a new class of narrow spectrum macrocyclic antibiotic drugs indicated for treatment of Clostridium difficile-associated diarrhea. Lipiarmycin (fidaxomicin), a metabolite of Actinoplanes deccanensis nov. sp. was first isolated in pure form in 1970s and was considered as antibiotic from its chemical and physico-chemical characteristics. It demonstrated high activity against Gram-positive bacteria, including strains resistant to the medically important antibiotics and protected mice experimentally infected with Streptococcus haemolyticus. Fidaxomicin is non-systemic, meaning it is minimally absorbed into the bloodstream, it is bactericidal, and it has demonstrated selective eradication of pathogenic Clostridium difficile with minimal disruption to the multiple species of bacteria that make up the normal, healthy intestinal flora. Although the exact mechanism of action has yet to be fully elucidated, fidaxomicin may bind to and inhibit bacterial DNA-dependent RNA polymerase, thereby inhibiting the initiation of bacterial RNA synthesis. When orally administered, this agent is minimally absorbed into the systemic circulation, acting locally in the gastrointestinal tract. Fidaxomicin appears to be active against pathogenic Gram-positive bacteria, such as clostridia, enterococci, and staphylococci, but does not appear to be active against other beneficial intestinal bacteria. The maintenance of normal physiological conditions in the colon can reduce the probability of Clostridium difficile infection recurrence. It is marketed by Cubist Pharmaceuticals after acquisition of its originating company Optimer Pharmaceuticals.