LFF-571 is a novel semisynthetic thiopeptide antibiotic with potent activity against a variety of Gram-positive pathogens, including Clostridium difficile. LFF-571 was generally safe and well tolerated in single and multiple oral doses in healthy subjects. There were no deaths, no serious adverse events, and no subject withdrawals due to an adverse event. The most common adverse event was diarrhea, gastrointestinal pain or distension was also noted. Similar to healthy volunteers, patients with C. difficile infections exhibited high fecal concentrations and low serum levels of LFF571. Novartis is developing oral LFF 571 for the treatment of Clostridium difficile infections. LFF 571 binds to bacterial elongation factor Tu (EF-Tu) in domain 2. Phase-II development is ongoing in USA and Canada.