Is meropenem (carbapenem antibiotic) effective for treating infections caused by Enterococcus faecium or Enterococcus faecalis?

Meropenem's Effectiveness Against Enterococcus faecium and Enterococcus faecalis

Meropenem is not effective against Enterococcus faecium or Enterococcus faecalis and should not be used as monotherapy for treating enterococcal infections. 1

Intrinsic Resistance of Enterococci to Carbapenems

• Enterococci have limited or no susceptibility to carbapenems, including meropenem, due to their intrinsic resistance mechanisms and low-affinity penicillin-binding proteins 1, 2
• While imipenem has some activity against enterococci, other carbapenems including meropenem have limited or no activity against these organisms 1
• Carbapenems (including meropenem) are specifically noted to lack activity against Enterococcus species in multiple guidelines 3, 1

Recommended Treatment Options for Enterococcal Infections

• For vancomycin-susceptible Enterococcus faecalis infections, ampicillin or penicillin G remains the drug of choice, often in combination with an aminoglycoside for synergistic effect 1
• For ampicillin-resistant enterococci that remain vancomycin-susceptible, vancomycin plus an aminoglycoside (if susceptible) is the recommended treatment 1
• For vancomycin-resistant enterococci (VRE), linezolid or tigecycline are recommended treatment options 1
• Tigecycline is specifically recommended as the drug of choice for intra-abdominal infections caused by vancomycin-resistant enterococci 1

Potential Combination Therapy Involving Meropenem

• Recent research suggests that meropenem plus ceftaroline may have activity against E. faecalis in vitro, but this is not yet supported by clinical guidelines 4
• This combination demonstrated significant kill against E. faecalis isolates in an in vitro pharmacodynamic model, comparable to the standard ampicillin plus ceftriaxone regimen 4
• However, this remains experimental and requires further clinical studies to determine efficacy in actual patients 4, 2

Clinical Implications and Recommendations

• When treating infections where enterococci are suspected or confirmed, avoid meropenem monotherapy as it will not provide adequate coverage 1
• For intra-abdominal infections where both Gram-negative bacteria and enterococci are concerns, combination therapy or alternative agents with broader spectrum should be considered 1
• The WHO Essential Medicines guidelines do not recommend carbapenems for empiric coverage of enterococci in intra-abdominal infections 1
• For serious enterococcal infections like endocarditis, follow established guidelines using ampicillin/penicillin plus aminoglycosides, or ampicillin plus ceftriaxone for aminoglycoside-resistant strains 1

Pitfalls and Caveats

• Relying on meropenem alone for infections where enterococci are likely pathogens may lead to treatment failure 1, 5
• Enterococcal resistance patterns vary geographically; local antibiograms should guide therapy 6, 2
• In polymicrobial infections involving both Gram-negative bacteria and enterococci, additional agents with enterococcal activity must be added if meropenem is used 1, 5
• The distinction between colonization and true infection with enterococci is important to avoid unnecessary treatment 1