From the FDA Drug Label
Enterococcus spp≤ 4 A report of "Susceptible" indicates that the pathogen is likely to be inhibited if the antimicrobial compound in the blood reaches the concentrations usually achievable
The concentration of less than 16 mcg/ml is adequate for susceptibility to antibiotics in enterococcal infections, as the susceptible MIC for Enterococcus spp is ≤ 4. 1
From the Research
No, a concentration of less than 16 micrograms per milliliter (mcg/ml) is not adequate for susceptibility to antibiotics in enterococcal infections. The minimum inhibitory concentration (MIC) breakpoint for susceptibility to vancomycin, which is often the antibiotic of choice for serious enterococcal infections, is ≤4 mcg/ml, as noted in studies such as 2. For ampicillin, another commonly used antibiotic, the susceptibility breakpoint is ≤8 mcg/ml.
When treating enterococcal infections, it's crucial to achieve antibiotic concentrations well above these MIC values at the site of infection to ensure effective bacterial killing. This typically requires higher serum concentrations, often in the range of 15-20 mcg/ml for vancomycin trough levels in serious infections, as discussed in 3 and 4. Inadequate antibiotic concentrations can lead to treatment failure and the development of resistance.
Additionally, enterococci have intrinsic resistance to many antibiotics, including cephalosporins and aminoglycosides when used alone, making appropriate dosing of effective antibiotics particularly important, as highlighted in 5 and 6. For serious enterococcal infections like endocarditis or meningitis, combination therapy with a cell-wall active agent (like ampicillin or vancomycin) plus an aminoglycoside (like gentamicin) is often recommended to achieve synergistic killing.
Key points to consider include:
- The importance of achieving adequate antibiotic concentrations to prevent treatment failure and resistance development
- The role of combination therapy in serious enterococcal infections
- The need for careful selection of antibiotics based on susceptibility testing, as emphasized in 4
- The potential for ampicillin to be effective in certain cases, as shown in 6, despite resistance concerns.
Overall, the management of enterococcal infections requires careful consideration of antibiotic susceptibility, dosing, and potential combinations to ensure effective treatment and minimize the risk of resistance.