In vitro, it is bactericidal against C. difficile and suppresses bacterial toxin production; the mechanism of action is thought to involve inhibition of cell division.[1] It has properties which are desirable for the treatment of CDI, namely that it is a narrow-spectrum antibiotic which exhibits activity against C. difficile while having little impact on other normal intestinal flora and that it is only minimally absorbed systemically after oral administration.[2] At the time ridinilazole was developed, there were only three antibiotics in use for treating CDI: vancomycin, fidaxomicin, and metronidazole.[1][2] The recurrence rate of CDI is high, which has spurred research into other treatment options with the aim to reduce the rate of recurrence.[3][4]