Micafungin 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
Micafungin inhibits the synthesis of 1, 3-beta-D-glucan, an essential component of fungal cell walls, which is not present in mammalian cells.
Drug Resistance
There have been reports of clinical failures in patients receiving Mycamine therapy due to the development of drug resistance. Some of these reports have identified specific mutations in the FKS protein component of the glucan synthase enzyme that are associated with higher MICs and breakthrough infection.
Activity In Vitro and In Clinical Infections
Micafungin has been shown to be active against most isolates of the following Candida species, both in vitro and in clinical infections:
Candida albicans Candida glabrata Candida guilliermondii Candida krusei Candida parapsilosis Candida tropicalis
Susceptibility Testing Methods
The interpretive standards for micafungin against Candida species are applicable only to tests performed using Clinical Laboratory and Standards Institute (CLSI) microbroth dilution reference method M27-A3 for minimum inhibitory concentration (MIC; based on partial inhibition endpoint) and CLSI disk diffusion reference method M44-A2; both MIC and zone diameter results are read at 24 hours.
When available, the clinical microbiology laboratory should provide the results of in vitro susceptibility test results for antimicrobial drug products used in resident hospitals to the physician as periodic reports that describe the susceptibility profile of pathogens. These reports should aid the physician in selecting an antifungal drug product for treatment. The techniques for Broth Microdilution and Disk Diffusion are described below.
Broth Microdilution Technique
Quantitative methods are used to determine antifungal MICs. These MICs provide estimates of the susceptibility of Candida species to antifungal agents. MICs should be determined using a standardized CLSI procedure1,2. Standardized procedures are based on a microdilution method (broth) with standardized inoculum concentrations and standardized concentrations of micafungin powder. The MIC values should be interpreted according to the criteria provided in Table 9.
Disk Diffusion Technique
Qualitative methods that require measurement of zone diameters also provide reproducible estimates of the susceptibility of Candida species to antifungal agents. The CLSI procedure3 uses standardized inoculum concentrations and paper disks impregnated with 10 mcg of micafungin to test the susceptibility of Candidaspecies to micafungin at 24 hours. Disk diffusion interpretive criteria are provided in Table 9.[1]
 |
A report of “Susceptible” indicates that the isolate is likely to be inhibited if the antimicrobial compound in the blood reaches the concentrations usually achievable.
The “Intermediate” category implies that an infection due to the isolate may be appropriately treated in body sites where the drug is physiologically concentrated or when a high dosage of drug is used. The “Resistant” category implies that the isolates are not inhibited by the concentrations of the drug usually achievable with normal dosage schedules and clinical efficacy of the drug against the pathogen has not been reliably shown in treatment studies.
Quality Control
Standardized susceptibility test procedures require the use of quality control organisms to monitor and ensure the accuracy and precision of supplies and reagents used in the assay, and the technique of the individual performing the test1, 2, 3. Standard micafungin powder and 10 mcg disks should provide the following range of values noted in Table 10.
 |
References
Adapted from the FDA Package Insert.