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Antimicrob Agents Chemother. 1981 December; 20(6): 747-759
Copyright © 1981, American Society for Microbiology. All Rights Reserved.

Cefmenoxime (SCE-1365), a new Cephalosporin: In Vitro Activity, Comparison with Other Antimicrobial Agents, Beta-Lactamase Stability, and Disk Diffusion Testing with Tentative Interpretive Criteria

Peter C. Fuchs¹, Ronald N. Jones², Clyde Thornsberry³, Arthur L. Barry⁴, E. Hugh Gerlach⁵ and Herbert M. Sommers⁶

¹ Department of Pathology, St. Vincent Hospital and Medical Center, Portland, Oregon 97225
² Department of Pathology, Kaiser Foundation Laboratory, Clackamas, Oregon 97015
³ Antimicrobics Investigations Section, Centers for Disease Control, Atlanta, Georgia 30333
⁴ Clinical Microbiology Laboratories, University of California, Davis, Medical Center, Sacramento, California 97817
⁵ Department of Laboratories, St. Francis Hospital, Wichita, Kansas 67214
⁶ Department of Pathology, Northwestern Memorial Hospital, Chicago, Illinois 60611

ABSTRACT

The in vitro activity of cefmenoxime (SCE-1365) was evaluated in a multiphased collaborative investigation. Over 7,500 consecutive clinical isolates were tested in five laboratories, and greater than 90% of the following organisms were inhibited by cefmenoxime at the following concentrations: Enterobacteriaceae and non-enterococcal streptococci, 0.125 µg/ml; Staphylococcus aureus, 2.0 µg/ml; and nonfermenting gram-negative bacilli and Bacteroides fragilis group, 32 µg/ml. Both beta-lactamase-producing and -nonproducing Haemophilus influenzae and Neisseria gonorrhoeae were inhibited by cefmenoxime at 0.03 µg/ml. The spectrum of cefmenoxime was similar to that of other, newer cephalosporins, particularly cefotaxime. A pronounced inoculum effect was found with some species upon increasing inocula from 10⁵ to 10⁷ colony-forming units per ml, resulting in an approximate eightfold increase in minimum inhibitory concentrations. Cefmenoxime was bactericidal when tested with inocula of 10⁵ colonyforming units per ml, and mean differences between the minimum inhibitory concentration and the minimum lethal concentration were less than one log₂ dilution. No significant hydrolysis of cefmenoxime by five different beta-lactamases was detectable, and cefmenoxime exhibited marked inhibition of type I beta-lactamases. Regression and error rate-bounded analyses of results of disk diffusion and reference broth microdilution susceptibility tests were performed on 421 bacterial isolates, and the following tentative zone size breakpoints are proposed: 22 mm, susceptible; 14 mm, resistant; and 15 to 21 mm, moderately susceptible (indeterminate). These data and cross-resistance studies with other newer cephalosporins indicate marked similarity of in vitro activity within this group of drugs, particularly between cefmenoxime, moxalactam, and cefotaxime. Any one of these could serve as the representative for the disk diffusion testing of this group of drugs if comparable minimum inhibitory concentration breakpoints were used for each drug.

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Antimicrob Agents Chemother. 1981 December; 20(6): 747-759
Copyright © 1981, American Society for Microbiology. All Rights Reserved.

This article has been cited by other articles:

• NEU, H. C. (1982). The New Beta-Lactamase-Stable Cephalosporins. ANN INTERN MED 97: 408-419 [Abstract]