Cookies on this website

We use cookies to ensure that we give you the best experience on our website. If you click 'Accept all cookies' we'll assume that you are happy to receive all cookies and you won't see this message again. If you click 'Reject all non-essential cookies' only necessary cookies providing core functionality such as security, network management, and accessibility will be enabled. Click 'Find out more' for information on how to change your cookie settings.

Omadacycline is a potent aminomethylcycline with <i>in vitro</i> activity against Gram-positive, Gram-negative, and anaerobic bacteria. Preliminary data demonstrated that omadacycline has <i>in vitro</i> activity against <i>Clostridioides difficile</i>; however, large-scale <i>in vitro</i> studies have not been done. The purpose of this study was to assess the <i>in vitro</i> susceptibility of omadacycline and comparators on a large biobank of clinical <i>C. difficile</i> isolates. <i>In vitro</i> <i>C. difficile</i> susceptibility to omadacycline and comparators (fidaxomicin, metronidazole, and vancomycin) was assessed using the broth microdilution method. Minimum bactericidal concentrations (MBCs) and time-kill assays were assessed for pharmacodynamics analysis, and whole-genome sequencing was performed in a subset of isolates to assess distribution of MICs and resistance determinants. Two hundred fifty clinical <i>C. difficile</i> isolates collected between 2015 and 2018 were tested for <i>in vitro</i> susceptibility of omadacycline and comparators. Ribotypes included F001 (<i>n</i> = 5), F002 (<i>n</i> = 56), F014-020 (<i>n</i> = 66), F017 (<i>n</i> = 8), F027 (<i>n</i> = 53), F106 (<i>n</i> = 45), and F255 (<i>n</i> = 17). Omadacycline demonstrated potent <i>in vitro</i> activity with an MIC range of 0.016 to 0.13 μg/ml, an MIC<sub>50</sub> of 0.031 μg/ml, and an MIC<sub>90</sub> of 0.031 μg/ml. No difference was observed for omadacycline MIC<sub>50</sub> and MIC<sub>90</sub> values stratified by ribotype, disease severity, or vancomycin susceptibility. Bactericidal activity was confirmed in time-kill studies. No difference was observed in MIC based on <i>C. difficile</i> phylogeny. Further development of omadacycline as an intravenous and oral antibiotic directed toward <i>C. difficile</i> infection is warranted.

Original publication




Journal article


Antimicrobial agents and chemotherapy

Publication Date





University of Houston College of Pharmacy, Houston, Texas, USA.