Abstract
The in vitro activities of ceftolozane-tazobactam, meropenem, and metronidazole were determined against anaerobic organisms isolated from patients with complicated intraabdominal infections (cIAI) in global phase III studies. Ceftolozane-tazobactam activity was highly variable among different species of the Bacteroides fragilis group, with MIC90 values ranging from 2 to 64 μg/ml. More-potent in vitro activity was observed against selected Gram-positive anaerobic organisms; however, small numbers of isolates were available, and, therefore, the clinical significance of these results is unknown. Variable activity of ceftolozane-tazobactam against anaerobic organisms necessitates use in combination with metronidazole for the treatment of cIAI.
TEXT
Ceftolozane-tazobactam is a novel antibacterial with activity against Pseudomonas aeruginosa, including drug-resistant strains, and other common Gram-negative pathogens, including most extended-spectrum-β-lactamase–producing Enterobacteriaceae (1, 2). Ceftolozane-tazobactam has been approved by the U.S. Food and Drug Administration for the treatment of complicated intraabdominal infections (cIAI) in combination with metronidazole (3). The in vitro activity of ceftolozane-tazobactam was determined against anaerobic pathogens identified at baseline during the global phase III studies of ceftolozane-tazobactam plus metronidazole versus meropenem in cIAI from 2011 to 2013 (ASPECT-cIAI; NCT01445665 and NCT01445678). In ASPECT-cIAI, ceftolozane-tazobactam plus metronidazole met its primary endpoint of noninferiority to meropenem for clinical cure at the test-of-cure visit in the microbiological intent-to-treat (MITT) population (4). The MITT population consisted of 806 patients, and 389 patients received treatment with ceftolozane-tazobactam. Of these, 137 patients (35.2%) had at least one Gram-negative anaerobic organism identified at baseline, and all but 3 patients had polymicrobial infections that included at least one aerobic organism (4).
Local laboratories from clinical study sites were responsible for the primary identification of all pathogens. All pathogens were required to be shipped to the central laboratory (ICON Laboratories, Farmingdale, NY, USA) for confirmation of identification and susceptibility testing. Anaerobic bacterial strains were shipped frozen in tryptic soy broth with 15% glycerol. Susceptibility testing was performed by broth microdilution in brucella broth supplemented with hemin, vitamin K1, and 5% lysed horse blood for Bacteroides fragilis group strains. Antibiotic susceptibility testing of B. fragilis group isolates and quality control (QC) were performed according to Clinical and Laboratory Standards Institute (CLSI) guidelines (5). Anaerobic isolates that were not B. fragilis group were shipped from ICON to JMI Laboratories (North Liberty, IA, USA) for susceptibility testing. Isolate MIC values for the non-fragilis group Bacteroides organisms were determined under anaerobic conditions using the reference CLSI agar dilution method (6). Agar dilution plates were produced by JMI Laboratories using brucella agar supplemented with hemin, vitamin K1, and 5% laked sheep blood. The B. fragilis ATCC 25285 QC strain was tested daily, and inoculum density was monitored by colony counts. All QC data were in range for both broth and agar dilution testing.
The in vitro activity of ceftolozane-tazobactam and comparators against anaerobic isolates identified in the ASPECT-cIAI study is presented in Table 1. Ceftolozane-tazobactam activity against Bacteroides fragilis group isolates was variable. The MIC90 against Bacteroides thetaiotaomicron and Bacteroides vulgatus was 64 μg/ml in each case, while Bacteroides fragilis and Bacteroides stercoris each displayed a ceftolozane-tazobactam MIC90 of 2 μg/ml. Other Gram-negative anaerobes identified in the study were Fusobacterium spp., Parabacteroides distasonis, and Prevotella spp. Ceftolozane-tazobactam was active against Prevotella spp., with an MIC90 of 0.06 μg/ml against the 10 isolates obtained.
TABLE 1.
In vitro activity of ceftolozane-tazobactam against anaerobes isolated at baseline from patients in ASPECT-cIAI
| Baseline pathogen (no.) | Antibiotic | MIC range (μg/ml) | MIC50 (μg/ml) | MIC90 (μg/ml) | % susceptiblea |
|---|---|---|---|---|---|
| Gram-negative anaerobes | |||||
| Bacteroides fragilis (107)b | Ceftolozane-tazobactam | 0.06 to >64 | 0.5 | 2 | 96.3 |
| Meropenem | 0.06 to 64 | 0.125 | 2 | 95.3 | |
| Metronidazole | 0.125 to 64 | 1 | 2 | 99.1 | |
| Bacteroides ovatus (87)b | Ceftolozane-tazobactam | 0.06 to >64 | 16 | 64 | NAc |
| Meropenem | 0.06 to 8 | 0.25 | 0.5 | 98.9 | |
| Metronidazole | 0.125 to 8 | 1 | 2 | 100 | |
| Bacteroides thetaiotaomicron (68)b | Ceftolozane-tazobactam | 0.06 to >64 | 32 | 64 | NA |
| Meropenem | 0.06 to 1 | 0.25 | 0.25 | 100 | |
| Metronidazole | 0.125 to 64 | 1 | 2 | 98.5 | |
| Bacteroides vulgatus (39)b | Ceftolozane-tazobactam | 1 to >64 | 16 | 64 | NA |
| Meropenem | 0.06 to 1 | 0.125 | 0.5 | 100 | |
| Metronidazole | 0.06 to 2 | 0.5 | 1 | 100 | |
| Parabacteroides distasonis (27)d | Ceftolozane-tazobactam | 16 to >64 | 64 | >64 | NA |
| Meropenem | 0.12 to 2 | 0.25 | 1 | 100 | |
| Metronidazole | 0.25 to 2 | 1 | 2 | 100 | |
| Bacteroides uniformis (15)b | Ceftolozane-tazobactam | 0.5 to 64 | 16 | 32 | NA |
| Meropenem | 0.06 to 1 | 0.125 | 0.5 | 100 | |
| Metronidazole | 0.125 to 8 | 0.5 | 4 | 100 | |
| Bacteroides stercoris (12)b | Ceftolozane-tazobactam | 0.06 to 2 | 0.125 | 2 | NA |
| Meropenem | 0.06 to 0.25 | 0.125 | 0.25 | 100 | |
| Metronidazole | 0.5 to 4 | 1 | 4 | 100 | |
| Fusobacterium spp. (11)d | Ceftolozane-tazobactam | ≤0.03 to >64 | ≤0.03 | >64 | NA |
| Meropenem | ≤0.015 to 1 | 0.06 | 1 | 100 | |
| Metronidazole | ≤0.12 to 1 | 0.25 | 0.5 | 100 | |
| Prevotella spp. (10)d | Ceftolozane-tazobactam | ≤0.03 to 16 | ≤0.03 | 0.06 | NA |
| Meropenem | 0.03 to 0.25 | 0.06 | 0.12 | 100 | |
| Metronidazole | ≤0.12 to >16 | 1 | 4 | 90.0 | |
| Bacteroides spp. (6)d | Ceftolozane-tazobactam | 0.5 to >64 | 1 | NA | NA |
| Meropenem | 0.12 to 1 | 0.12 | NA | 100 | |
| Metronidazole | 0.25 to 1 | 0.5 | NA | 100 | |
| Gram-positive anaerobes | |||||
| Clostridium perfringens (45)d | Ceftolozane-tazobactam | ≤0.03 to 16 | 0.06 | 0.5 | NA |
| Meropenem | ≤0.015 to 0.12 | ≤0.015 | 0.03 | 100 | |
| Metronidazole | ≤0.12 to >16 | 1 | 2 | 97.8 | |
| Propionibacterium acnes (8)d | Ceftolozane-tazobactam | ≤0.03 to 16 | 2 | NA | NA |
| Meropenem | ≤0.015 to 1 | 0.06 | NA | 100 | |
| Metronidazole | >16 | >16 | NA | 0 | |
| Eggerthella lenta (6)d | Ceftolozane-tazobactam | >64 | >64 | NA | NA |
| Meropenem | 0.25 | 0.25 | NA | 100 | |
| Metronidazole | 0.25 to 2 | 0.25 | NA | 100 | |
| Eubacterium spp. (5)d | Ceftolozane-tazobactam | 0.5 to 4 | 1 | NA | NA |
| Meropenem | 0.03 to 0.25 | 0.06 | NA | 100 | |
| Metronidazole | 0.25 to 8 | 0.5 | NA | 100 | |
| Parvimonas micra (5)d | Ceftolozane-tazobactam | ≤0.03 to 4 | ≤0.03 | NA | NA |
| Meropenem | ≤0.015 to 0.5 | ≤0.015 | NA | 100 | |
| Metronidazole | 0.25 to 0.5 | 0.25 | NA | 100 | |
| Slackia exigua (3)d | Ceftolozane-tazobactam | ≤0.03 to 16 | 0.06 | NA | NA |
| Meropenem | 0.03 to 0.12 | 0.06 | NA | 100 | |
| Metronidazole | 0.25 to 0.5 | 0.5 | NA | 100 | |
| Other (6)d,d | Ceftolozane-tazobactam | 0.5 to 2 | 1 | NA | NA |
| Meropenem | 0.06 to 0.25 | 0.12 | NA | 100 | |
| Metronidazole | 0.5 to >16 | 4 | NA | 50.0 |
Ceftolozane-tazobactam susceptibility of Bacteroides fragilis isolates was calculated based on the U.S. Food and Drug Administration breakpoint of 8 μg/ml for Bacteroides fragilis. Susceptibilities of meropenem and metronidazole were calculated based on breakpoints published by the Clinical and Laboratory Standards Institute (M100-S22) (7).
Broth microdilution, ICON Laboratories.
NA, not available.
Agar dilution, JMI Laboratories.
Other Gram-positive pathogens consisted of Bifidobacterium spp. (n = 2), Peptoniphilus asaccharolyticus (n = 2), Collinsella aerofaciens (n = 1), and Peptostreptococcus anaerobius (n = 1).
Ceftolozane-tazobactam was also active in vitro against the most prevalent Gram-positive anaerobic species identified, with an MIC90 of 0.5 μg/ml against the 45 isolates of Clostridium perfringens. Activity was variable against the remaining Gram-positive anaerobic organisms, each with fewer than 9 isolates available from the clinical trial.
Among Bacteroides fragilis group isolates, the ceftolozane-tazobactam MIC90 values were within one dilution of those published in an earlier study (8). However, the MIC50 values were generally lower in the surveillance study than those observed with ASPECT-cIAI isolates. Activity levels of ceftolozane-tazobactam against non-B. fragilis Gram-negative anaerobes were generally similar between the two studies. The activities of metronidazole and meropenem were unchanged relative to the surveillance study.
The in vitro results support the clinical findings of the phase III ASPECT-cIAI study, demonstrating the utility of ceftolozane-tazobactam in combination with metronidazole for the treatment of patients with cIAI. An application for approval of ceftolozane-tazobactam in combination with metronidazole has also been submitted to the European Medicines Agency.
ACKNOWLEDGMENTS
Editorial assistance was provided by Jean Turner of Parexel and funded by Merck & Co., Inc., Kenilworth, NJ, USA.
Eliana S. Armstrong is working under a contract from Pro Unlimited, Boca Raton, FL, USA.
Eliana S. Armstrong, Melissa Palchak, and Judith N. Steenbergen are employees of Merck, Sharp, & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA. David J. Farrell is an employee of JMI Laboratories, Inc., which has received research and educational grants from 2009 to 2014 from Achaogen, Actavis, Aires, American Proficiency Institute (API), Anacor, Astellas, AstraZeneca, Bayer, bioMérieux, Cempra, ContraFect, Cubist Pharmaceuticals, Daiichi, Dipexium, Enanta, Furiex, GlaxoSmithKline, Johnson & Johnson, LegoChemBiosciences Inc., Meiji Seika Kaisha, Melinta Therapeutics, Merck Sharp & Dohme Corp., a subsidiary of Merck & and Co., Inc., Nabriva, Novartis, Paratek, Pfizer, PPD Therapeutics, Premier Research group, Rempex, Seachaid, Shionogi, The Medicines Co., Theravance, and Thermo Fisher. Some JMI employees are advisors/consultants for Astellas, Cubist Pharmaceuticals, Pfizer, Cempra, Actavis, Johnson & Johnson, and Theravance.
Funding Statement
This study was funded by Merck & Co., Inc., Kenilworth, NJ, USA.
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