C1-3842. In Vitro Activity of Cethromycin (CER) Against Toxigenic Clostridium difficile Clinical Isolates
Session: Poster Session: Miscellaneous
Tuesday, October 28, 2008: 12:00 AM
Room: Hall C
Background: C. difficile is the major cause of antibiotic-associated diarrhea. CER, is a novel ketolide antibiotic with activity against gram-positive bacteria resistant to penicillin, macrolides and quinolones, and is in development for treatment of community acquired pneumonia. Ketolide antibiotics are less often associated with alteration of the intestinal microflora or with C. difficile colonization. With only vancomycin (VAN) and metronidazole (MTZ) as first line therapy, the search for new agents with activity against C. difficile is warranted. We investigated the in vitro activity of CER against C. difficile isolates. Methods: 110 unique toxigenic C. difficile isolates of differing REA type known to have caused CDI were utilized for susceptibility testing. Inoculum preparation and agar dilution were performed according to the CLSI method for anaerobes (M11-A7). ATCC 700057 strain was included as the control and CER was assayed alongside VAN and MTZ. Results: Cethromycin demonstrated in vitro activity with a geometric mean MIC and MIC50 in between those of MTZ and VAN. 80% of the tested isolates had cethromycin MICs of 0.03 - 4 μg/mL with the MIC90 being 128 µg/mL.
MIC (μg/mL)
RangeGeometric Mean50%90%
CER0.03 - 1280.5270.125128
VAN0.5 - 41.04512
MTZ0.125 - 20.2480.250.25
Conclusions: CER had good in vitro activity against a majority of C. difficile isolates tested. If confirmed in clinical trials, this activity, combined with the preservation of normal intestinal flora of ketolide antibiotics including CER, may lessen the likelihood of developing CDI while being treated with CER and reduce recurrence of CDI if it is treated with CER compared with other agents.
D Eiznhamer1, Dale Gerding, MD, FIDSA2, David Hecht, MD, MS, MBA, FIDSA3, James Osmolski, BS3, M English4, M Flavin1, Z Xu4 and  D. W. Hecht,
Advanced Life Sciences Role(s): Grant Investigator, Received: Grant Recipient., (1)Advanced Life Science, (2)Hines VA Hospital, Hines, IL, (3)Loyola University Medical Center, Maywood, IL, (4)Advanced Life Sciences

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