Mechanism of Action
Cefepime is a bactericidal drug that acts by inhibition of bacterial cell wall synthesis. Cefepime has a broad spectrum of in vitro activity that encompasses a wide range of Gram-positive and Gram-negative bacteria. Within bacterial cells, the molecular targets of cefepime are the penicillin binding proteins (PBP).
Antimicrobial Activity
Cefepime has been shown to be active against most isolates of the following microorganisms, both in vitro and in clinical infections as described in the Indications and Usage section (1).
Gram-negative Bacteria
Enterobacter spp.
Escherichia coli
Klebsiella pneumoniae
Proteus mirabilis
Pseudomonas aeruginosa
Gram-positive Bacteria
Staphylococcus aureus (methicillin-susceptible isolates only)
Streptococcus pneumoniae
Streptococcus pyogenes
Viridans group streptococci
The following in vitro data are available, but their clinical significance is unknown. At least 90 percent of the following bacteria exhibit an in vitro minimum inhibitory concentration (MIC) less than or equal to the susceptible breakpoint for cefepime against isolates of similar genus or organism group. However, the efficacy of cefepime in treating clinical infections due to these bacteria has not been established in adequate and well-controlled clinical trials.
Gram-positive Bacteria
Staphylococcus epidermidis (methicillin-susceptible isolates only)
Staphylococcus saprophyticus
Streptococcus agalactiae
NOTE: Most isolates of enterococci, e.g., Enterococcus faecalis, and methicillin-resistant staphylococci are resistant to cefepime.
Gram-negative Bacteria
Acinetobacter calcoaceticus subsp. lwoffii
Citrobacter diversus
Citrobacter freundii
Enterobacter agglomerans
Haemophilus influenzae
Hafnia alvei
Klebsiella oxytoca
Moraxella catarrhalis
Morganella morganii
Proteus vulgaris
Providencia rettgeri
Providencia stuartii
Serratia marcescens
NOTE: Cefepime is inactive against many isolates of Stenotrophomonas maltophilia.
Susceptibility Test Methods
When available, the clinical microbiology laboratory should provide cumulative reports of in vitro susceptibility test results for antimicrobial drugs used in local hospitals and practice areas 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 for treatment.
Dilution techniques
Quantitative methods are used to determine antimicrobial minimum inhibitory concentrations (MICs). These MICs provide estimates of the susceptibility of bacteria to antimicrobial compounds. The MICs should be determined using a standardized test method1,2 (broth and/or agar). The MIC should be interpreted according to criteria provided in Table 10.
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 should be determined using a standardized test method.2,3 This procedure uses paper discs impregnated with 30 mcg cefepime to test the susceptibility of microorganisms to cefepime. The disk diffusion interpretive criteria are provided in Table 10.
Table 10: Susceptibility Test Interpretive Criteria for Cefepime¥
Pathogen
| Minimum Inhibitory Concentrations (mcg/mL)
| Disk Diffusion Zone Diameters (mm)
|
(S) Susceptible
| (I) Intermediate
| (R) Resistant
| (S) Susceptible
| (I) Intermediate
| (R) Resistant
|
Enterobacteriaceae
| ≤2
| 4 to 8*
| ≥16
| ≥25
| 19 to 24*
| ≤18
|
Pseudomonas aeruginosa§
| ≤8
| -
| ≥16
| ≥18
| -
| ≤17
|
Streptococcus pneumoniaeb non-meningitis isolates
| ≤1
| 2
| ≥4
| -
| -
| -
|
Streptococcus pyogenes
| ≤0.5
| -
| -
| ≥24
| -
| -
|
Viridans group streptococci
| ≤1
| 2
| ≥4
| ≥24
| 22 to 23
| ≤21
|
¥For patients with renal impairment see Table 2 in Dosage and Administration.
*For isolates of Enterobacteriaceae with intermediate susceptibility, use a dose of 2 g every 8 hours in patients with normal renal function.
§For P. aeruginosa, use 2 g IV every 8 hours in patients with normal renal function
bFor non-meningitis isolates, a penicillin MIC of < 0.06 mcg/mL (or oxacillin zone > 20 mm) can predict susceptibility to cefepime.
Susceptibility of staphylococci to cefepime may be deduced from testing only penicillin and either cefoxitin or oxacillin.
A report of Susceptible (S) indicates that the antimicrobial drug is likely to inhibit growth of the pathogen if the antimicrobial drug reaches the concentration usually achievable at the site of infection. A report of Intermediate (I) 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 or in situations where a high dosage of the drug can be used. This category also provides a buffer zone that prevents small uncontrolled technical factors from causing major discrepancies in interpretation. A report of Resistant (R) indicates that the antimicrobial drug is not likely to inhibit growth of the pathogen if the antimicrobial drug reaches the concentration usually achievable at the infection site; other therapy should be selected.
Quality Control
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 individual performing the test.1,2,3 Standard cefepime powder should provide the following range of MIC values noted in Table 11. For the diffusion technique using the 30 mcg disc, the criteria in Table 11 should be achieved.
Table 11: Acceptable Quality Control Ranges for Cefepime
QC Strain
| Minimum Inhibitory Concentrations (mcg/mL)
| Disk Diffusion (zone diameters in mm)
|
Escherichia coli ATCC 25922
| 0.015 to 0.12
| 31 to 37
|
Staphylococcus aureus ATCC 29213
| 1 to 4
| -
|
Staphylococcus aureus ATCC 25923
| -
| 23 to 29
|
Pseudomonas aeruginosa ATCC 27853
| 0.5 to 4
| 24 to 30
|
Streptococcus pneumoniae ATCC 49619
| 0.03 to 0.25
| 28 to 35
|
Haemophilus influenzae ATCC 49247
| 0.5 to 2
| 25 to 31
|
Neisseria gonorrhoeae ATCC 49226
| 0.015 to 0.06
| 37 to 46
|