Andrew Skinner

Background Omadacycline is a novel aminomethylcycline tetracycline antimicrobial that was approved for the treatment of community-associated bacterial pneumonia (CABP) and acute bacterial skin and skin structure infections (ABSSSI) in 2018. Omadacycline has demonstrated a high degree of in vitro activity towards Clostridioides difficile and previous data have hypothesized that use of omadacycline for CABP or ABSSSI may decrease the risk of C. difficile infections. Objectives To compare the in vitro antimicrobial activity of omadacycline versus commonly used antimicrobials for the approved indications of use. Methods We compared the antimicrobial activity of eight antimicrobials approved for CABP and ABSSSI against omadacycline by agar dilution on 200 clinically relevant contemporary C. difficile isolates representing local and national prevalent strain types. Results The in vitro omadacycline geometric mean MIC was 0.07 mg/L. Ceftriaxone resistance was noted in >50% of all isolates tested. The epidemic strain group, identified as restriction endonuclease analysis (REA) group BI, was commonly resistant to azithromycin (92%), moxifloxacin (86%) and clindamycin (78%). REA group DH strains had an elevated trimethoprim/sulfamethoxazole geometric mean MIC of 17.30 mg/L compared with the geometric mean MIC of 8.14 mg/L noted in all other isolates. In the REA group BK isolates that had a doxycycline MIC of ≥2 mg/L, the omadacycline MIC was <0.5 mg/L. Conclusions Among 200 contemporary C. difficile isolates, there were no notable elevations in the in vitro omadacycline MIC, indicating a high level of activity towards C. difficile in comparison with commonly used antimicrobials for CABP and ABSSSI.