Cefixime microbiology
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Ahmed Zaghw, M.D. [2]
Microbiology
Mechanism of Action
Bactericidal action of cefixime results from inhibition of cell-wall synthesis.
Cefixime has been shown to be active against most isolates of the following bacteria both in vitro and in clinical infections [see INDICATIONS AND USAGE (1)]:
- Gram-positive bacteria
The following in vitro data are available, but their clinical significance is unknown. Suprax exhibits in vitro MICs of 1 mcg/mL or less against most (≥ 90%) isolates of the following bacteria; however, the safety and effectiveness of Suprax in treating clinical infections due to these bacteria have not been established in adequate and well-controlled clinical trials.
- Haemophilus parainfluenzae
- Providencia species
- Salmonella species
- Shigella species
- Citrobacter amalonaticus
- Citrobacter diversus
- Serratia marcescens
Susceptibility Tests Methods
When available, the clinical microbiology laboratory should provide the results of in vitro susceptibility test results for antimicrobial drugs used in resident hospitals to the physician as periodic reports that describe the susceptibility profile of nosocomial and community-acquired pathogens. These reports should aid the physician in selecting an antibacterial drug product for treatment.
Dilution Techniques: Quantitative methods are used to determine the minimum inhibitory concentrations (MICs). These MICs provide estimates of the susceptibility of bacteria to antimicrobial compounds. The MICs should be determined using standardized test methods 1,2 (broth, and/or agar). The MIC values should be interpreted according to the criteria in Table 3.
Diffusion Techniques: Quantitative methods that require measurement of zone diameters can also provide reproducible estimates of the susceptibility of bacteria to antimicrobial compounds. The zone size provides an estimate of the susceptibility of bacteria to antimicrobial compounds. The zone size should be determined using standardized method.2,3 This procedure uses paper disks impregnated with 5 mcg of cefixime to test the susceptibility of bacteria to cefixime. The disk diffusion interpretive criteria are provided in Table 3.
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A report of "Susceptible" indicates that the antimicrobial is likely to inhibit growth of the pathogen if the antimicrobial compound reaches the concentration at the infection site necessary to inhibit growth of the pathogen. A report of "Intermediate" indicates that the result should be considered equivocal, and if the microorganism is not fully susceptible to alternative clinically feasible drugs, the test should be repeated. This category implies possible clinical applicability in body sites where the drug is physiologically concentrated. This category also provides a buffer zone that prevents small uncontrolled technical factors from causing major discrepancies in interpretation. A report of "Resistant" indicates that the antimicrobial is not likely to inhibit growth of the pathogen if the antimicrobial compound reaches the concentrations usually achievable at the infection site; other therapy should be selected.
Quality Control in susceptibility
Standardized susceptibility test procedures require the use of laboratory controls to monitor and ensure the accuracy and precision of supplies and reagents used in the assay, and the techniques of the individuals performing the test.1, 2, 3 The standard cefixime powder should provide the following range of MIC values provided in Table 4. For the diffusion technique using the 5-mcg cefixime disk the criteria provided in Table 4 should be achieved.[1]
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References
Adapted from the FDA Package Insert.