From the Guidelines
A Minimum Inhibitory Concentration (MIC) of 16 μg/mL is considered resistant and alternative antibiotics should be considered. This value is significantly higher than the susceptible breakpoint, indicating that the bacteria are likely to be resistant to the antibiotic being tested 1. When encountering an MIC of 16, clinicians should consider alternative antibiotics with better susceptibility profiles if available.
- The clinical context is crucial in determining the best course of action, including factors like the specific bacteria, the antibiotic being tested, the infection site, and patient characteristics.
- For vancomycin, the guidelines suggest that for isolates with a vancomycin MIC ≥2 μg/mL, an alternative to vancomycin should be considered 1.
- If the antibiotic must be used despite this MIC, higher dosing regimens may be necessary to achieve adequate drug concentrations at the infection site, and therapeutic drug monitoring would be essential to maintain effective levels.
- The MIC value of 16 μg/mL suggests that standard dosing might be insufficient, and adjusting the treatment plan based on this information is critical to ensure the best possible outcome for the patient.
From the FDA Drug Label
The MIC values should be interpreted according to criteria provided in Table 4 Table 4 Susceptibility Interpretive Criteria for Linezolid PathogenSusceptibility Interpretive Criteria Minimal Inhibitory Concentrations(MIC in µg/mL) Disk Diffusion(Zone Diameters in mm) Enterococcus spp≤ 4------≥ 23------ Staphylococcus spp ≤4------ Streptococcus pneumoniae≤2†------ Streptococcus spp other than S pneumoniae*≤2†------
An MIC of 16 is considered Resistant for Enterococcus spp and Staphylococcus spp, as it is above the susceptible breakpoint of ≤ 4. For Streptococcus pneumoniae and Streptococcus spp other than S pneumoniae, an MIC of 16 is also considered Resistant, as it is above the susceptible breakpoint of ≤ 2 2.
From the Research
Minimum Inhibitory Concentration (MIC)
- The MIC is the lowest concentration of an antibiotic that will inhibit the growth of an organism 3
- Bacteria are classified as sensitive, intermediate, or resistant based on breakpoint MIC values that are arbitrarily defined and reflect the achievable levels of the antibiotic, the distribution of MICs for the organism, and their correlation with clinical outcome 3
MIC of 16
- There is no direct information available in the provided studies regarding an MIC of 16
- However, studies have discussed the importance of MIC in determining the effectiveness of antibiotics, such as vancomycin, in treating infections like methicillin-resistant Staphylococcus aureus (MRSA) 4, 5, 6
- The MIC of vancomycin is used to guide the selection of antibiotics for MRSA infections, with alternative therapeutic options considered when the MIC is 2 μg/mL or more 5
Treatment of MRSA Infections
- Initial treatment for MRSA infections typically includes antibiotics active against MRSA, such as vancomycin or daptomycin 4
- The choice of antibiotic may depend on the MIC of the organism, with alternative options considered when the MIC is high 5
- Combination antibiotic treatment is also being explored as an alternative to vancomycin, although more research is needed to determine its effectiveness 7