From the Guidelines
Meropenem (Merrem) does not reliably cover Enterococcus faecalis and should not be used as monotherapy for infections caused by this organism. While meropenem has broad-spectrum activity against many gram-positive and gram-negative bacteria, Enterococcus faecalis has intrinsic resistance mechanisms that limit meropenem's effectiveness. For E. faecalis infections, ampicillin or penicillin is typically the first-line therapy for susceptible strains, often combined with an aminoglycoside like gentamicin for synergistic effect in serious infections such as endocarditis 1. For penicillin-allergic patients or resistant strains, vancomycin is commonly used. The reason for E. faecalis's reduced susceptibility to carbapenems like meropenem relates to the organism's altered penicillin-binding proteins, which have lower affinity for carbapenem antibiotics.
Some key points to consider when treating E. faecalis infections include:
- The importance of combination therapy, such as penicillin or ampicillin with gentamicin, for serious infections like endocarditis 1
- The need to consider vancomycin for penicillin-allergic patients or resistant strains 1
- The potential for emerging resistance to vancomycin and other antibiotics, highlighting the need for careful antibiotic selection and monitoring 1
- The role of infectious disease consultation in managing patients with enterococcal infections, particularly in cases of complicated or resistant infections 1
In terms of specific antibiotic recommendations, the most recent and highest-quality study 1 suggests that ampicillin or penicillin, often combined with an aminoglycoside, remains a first-line option for E. faecalis infections. However, it's essential to consider local resistance patterns and patient-specific factors when selecting an antibiotic regimen. In general, meropenem should not be relied upon as a sole agent for treating E. faecalis infections, and instead, antibiotics with proven activity against this organism should be chosen.
From the FDA Drug Label
Meropenem for injection is indicated for the treatment of complicated skin and skin structure infections (cSSSI) due to ... Enterococcus faecalis (vancomycin-susceptible isolates only)...
- Merrem (meropenem) covers Enterococcus faecalis, but only for vancomycin-susceptible isolates.
- The use of meropenem for injection is recommended for the treatment of infections caused by susceptible bacteria, including vancomycin-susceptible Enterococcus faecalis 2.
From the Research
Merrem Coverage for Enterococcus Faecalis
- Meropenem, also known as Merrem, has a broad spectrum of in vitro activity against Gram-positive and Gram-negative pathogens, including some Enterococcus species 3, 4.
- However, Enterococcus faecium is uniformly resistant to meropenem, while Enterococcus faecalis may be susceptible, but with higher MICs than some other pathogens 3.
- A study found that meropenem plus ceftaroline was active against Enterococcus faecalis in an in vitro pharmacodynamic model using humanized dosing simulations, and may provide an alternative regimen for treating severe E. faecalis infections 5.
- The MICs of meropenem for Enterococcus faecalis are not consistently reported, but one study found that meropenem MICs for penicillin-resistant Streptococcus pneumoniae were higher than for penicillin-susceptible strains, suggesting that meropenem may have reduced activity against some Gram-positive pathogens 3.
- Clinical susceptibility to meropenem is defined by MICs of ≤ 4 mg/L, and Enterococcus faecalis isolates with MICs above this threshold may be considered resistant 3.
Key Findings
- Meropenem has in vitro activity against Enterococcus faecalis, but the extent of this activity may vary depending on the specific isolate and the presence of resistance mechanisms 5, 3.
- Meropenem plus ceftaroline may be an effective alternative regimen for treating severe E. faecalis infections, but further studies are needed to confirm this finding 5.
- The use of meropenem against Enterococcus faecalis should be guided by susceptibility testing and clinical judgment, taking into account the potential for resistance and the availability of alternative treatment options 3, 4.