Cefpodoxime microbiology
Cefpodoxime is active against a wide spectrum of Gram-positive and Gram-negative bacteria. Cefpodoxime is stable in the presence of beta-lactamase enzymes. As a result, many organisms resistant to penicillins and cephalosporins, due to their production of beta-lactamase, may be susceptible to cefpodoxime. Cefpodoxime is inactivated by certain extended spectrum beta-lactamases.
The bactericidal activity of cefpodoxime results from its inhibition of cell wall synthesis.
Cefpodoxime has been shown to be active against most strains of the following microorganisms, both in vitro and in clinical infections, as described in theINDICATIONS AND USAGE section.
Aerobic Gram-positive microorganisms: 
Staphylococcus aureus (including penicillinase-producing strains)
NOTE: Cefpodoxime is inactive against methicillin-resistant staphylococci.
Staphylococcus saprophyticus 
Streptococcus pneumoniae (excluding penicillin-resistant strains)
Streptococcus pyogenes
Aerobic Gram-negative microorganisms: 
Escherichia coli
Klebsiella pneumoniae
Proteus mirabilis
Haemophilus influenzae (including beta-lactamase producing strains)
Moraxella (Branhamella) catarrhalis
Neisseria gonorrhoeae (including penicillinase-producing strains)
The following in vitro data are available, but their clinical significance is unknown. Cefpodoxime exhibits in vitro minimum inhibitory concentrations (MICs) of  2.0 mcg/mL against most (90%) of isolates of the following microorganisms. However, the safety and efficacy of cefpodoxime in treating clinical infections due to these microorganisms have not been established in adequate and well-controlled clinical trials.
Aerobic Gram-positive microorganisms: 
Streptococcus agalactiae
Streptococcus spp. (Groups C, F, G)
NOTE: Cefpodoxime is inactive against enterococci.
Aerobic Gram-negative microorganisms: 
Citrobacter diversus
Klebsiella oxytoca
Proteus vulgaris
Providencia rettgeri
Haemophilus parainfluenzae 
NOTE: Cefpodoxime is inactive against most strains of Pseudomonas and Enterobacter.
Anaerobic Gram-positive microorganisms:
Peptostreptococcus magnus

# SUSCEPTIBILITY TESTING
Dilution Techniques
Quantitative methods are used to determine antimicrobial inhibitory concentrations (MICs). These MICs provide estimates of the susceptibility of microorganisms to antimicrobial compounds. The MICs should be determined using a standardized procedure. Standardized procedures are based on dilution methods1,2 (broth or agar) or equivalent using standardized inoculum concentrations, and standardized concentrations of cefpodoxime from a powder of known potency. The MIC values should be interpreted according to the following criteria:

# For Susceptibility Testing of Streptococcus spp. other than Streptococcus pneumonia.
A streptococcal isolate that is susceptible to penicillin (MIC 0.12 mcg/mL) can be considered susceptible to cefpodoxime for approved indications, and need not be tested against cefpodoxime.
A report of "Susceptible" indicates that the pathogen is likely to be inhibited if the concentration of the antimicrobial compound in the blood reaches usually achievable levels. A report of "Intermediate" indicates that the results 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 high dosage of drug can be used. This category also provides a buffer zone which prevents small technical factors from causing major discrepancies in interpretation. A report of "Resistant" indicates that the pathogen is not likely to be inhibited if the antimicrobial compound in the blood reaches the concentrations usually achievable; other therapy should be selected.
The interpretive value for Streptococcus spp. is applicable only to broth microdilution susceptibility testing done with cation-adjusted Mueller-Hinton broth with lysed horse blood (LHB) (25% v/v).2
Quality Control
A standardized susceptibility test procedure requires the use of laboratory control organisms to control the technical aspects of the laboratory procedures. Standard cefpodoxime powder should provide the following MIC values with the indicated quality control strains:
File:Cefpo5.png
Diffusion Techniques
Quantitative methods that require measurement of zone diameters also provide reproducible estimates of the susceptibility of bacteria to antimicrobial compounds. One such standardized procedure requires the use of standardized inoculum concentrations. This procedure uses paper disks impregnated with 10 mcg cefpodoxime to test the susceptibility of microorganisms to cefpodoxime. Reports from the laboratory providing results of the standard single-disk susceptibility test with a 10 mcg cefpodoxime disk should be interpreted according to the following criteria:

# For Susceptibility Testing of Streptococcus pneumoniae.
Isolates of pneumococci with oxacillin zone sizes of 20 mm are susceptible (MIC 0.06 mcg/mL) to penicillin and can be considered susceptible to cefpodoxime for approved indications, and cefpodoxime need not be tested.
For Susceptibility Testing of Streptococcus spp. other than Streptococcus pneumoniae.3
A streptococcal isolate that is susceptible to penicillin (zone diameter 28 mm) can be considered susceptible to cefpodoxime for approved indications, and cefpodoxime need not be tested.
The zone diameter for S. pneumoniae is applicable only to tests performed on Mueller-Hinton agar with 5% sheep blood incubated in 5% CO2.2
The zone diameter for Streptococcus spp. is applicable only to tests performed on Mueller-Hinton agar with 5% sheep blood incubated in 5% CO2.2
Quality Control
As with standardized dilution techniques, diffusion methods require the use of laboratory control microorganisms that are used to control the technical aspects of the laboratory procedures. For the diffusion technique, the 10 mcg cefpodoxime disk should provide the following zone diameters with the quality control strains listed below:
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