Amikacin, an aminoglycoside, binds to the prokaryotic ribosome, inhibiting protein synthesis in susceptible bacteria. It is bactericidal in vitro against Gram-positive and Gram-negative bacteria.
Aminoglycosides are known to be ineffective against Salmonella and Shigella species in patients. Therefore, in vitro susceptibility test results should not be reported.
Amikacin resists degradation by certain aminoglycoside inactivating enzymes known to affect gentamicin, tobramycin, and kanamycin.
Aminoglycosides in general have a low order of activity against Gram-positive organisms other than Staphylococcal isolates.
In vitro studies have shown that amikacin sulfate combined with a beta-lactam antibiotic acts synergistically against many clinically significant Gram-negative organisms.
Amikacin has been shown to be active against the following bacteria, both in vitro and in clinical infections [see INDICATIONS AND USAGE ].
Proteus species (indole-positive and indole-negative)
Serratia speciesAcinetobacter species
Amikacin has demonstrated in vitro activity against the following bacteria. The safety and effectiveness of amikacin in treating clinical infections due to these bacteria have not been established in adequate and well-controlled trials.
When available, the clinical microbiology laboratory should provide cumulative results of the in vitro susceptibility tests 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 the most effective antimicrobial.
Quantitative methods are used to determine antimicrobial minimal inhibitory concentrations (MICs). These MICs provide estimates of the susceptibility of bacteria to antimicrobial compounds. The MICs should be determined using a standardized test method.1, 3 Standardized procedures are based on a dilution method (broth or agar) or equivalent with standardized inoculum concentrations and standardized concentrations of amikacin powder. The MIC values should be interpreted according to the criteria provided in Table 1.
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 and paper disks impregnated with 30 mcg of amikacin.2, 3 The disk diffusion values should be interpreted according to the criteria provided in Table 1.
|Pathogen||Minimum InhibitoryConcentrations(mcg/mL)||Disk DiffusionZone Diameters(mm)|
|Enteriobacteriaceae *||≤ 16||32||≥ 64||≥ 17||15-16||≤ 14|
|Pseudomonas aeruginosa||≤ 16||32||≥ 64||≥ 17||15-16||≤ 14|
|Acinetobacter spp.||≤ 16||32||≥ 64||≥ 17||15-16||≤ 14|
|Other Non-Enterobacteriaceae||≤ 16||32||≥ 64||-||-||-|
|Staphylococcus spp.†||≤ 16||32||≥ 64||≥ 17||15-16||≤ 14|
S = susceptible, I = intermediate, R = resistant
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.
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 Standard amikacin powder should provide the following range of MIC values provided in Table 2. For the diffusion technique using the 30-mcg amikacin disk the criteria provided in Table 2 should be achieved.
|Quality ControlOrganism||Minimum Inhibitory Concentrations (mcg/mL)||Disk Diffusion Zone Diameters (mm)|
|Escherichia coli ATCC 25922||0.5-4||19-26|
|Pseudomonas aeruginosa ATCC 27853||1-4||18-26|
|Staphylococcus aureus ATCC 25923||Not Applicable||20-26|
|Staphylococcus aureu s ATCC 29213||1-4||Not Applicable|
|Enterococcus faecalis ATCC 29212||64-256||Not Applicable|
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