 Bezlotoxumab is not an antibiotic, but it is used to in conjunction with antibiotics to increase their effectiveness in treating CDI.Other pharmaceutical companies working on drugs to treat CDI include Synthetic Biologics, Sanofi, and Shire.Ridinilazole was approved for Phase III clinical trials after a successful Phase II ('CoDIFY') study showed that ridinilazole was tolerated at all doses and has a highly selective profile.