Ridinilazole (previously known as SMT19969) is an investigational small molecule antibiotic being evaluated for oral administration to treat Clostridioides difficile infection (CDI).

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][5][6] Ridinilazole was designated as a Qualified Infectious Disease Product (QIDP) and was granted Fast Track status by the U.S.

[2] Fast Track status is reserved for drugs designed to treat diseases where there is currently a gap in the treatment, or a complete lack thereof.