Meropenem Bacterial Coverage
Meropenem provides ultra-broad spectrum coverage against Gram-positive and Gram-negative aerobic bacteria plus anaerobes, with particular strength against multidrug-resistant Gram-negative pathogens including ESBL-producers, AmpC-hyperproducers, and Pseudomonas aeruginosa. 1, 2
Gram-Negative Coverage (Primary Strength)
Meropenem demonstrates exceptional activity against Gram-negative organisms, which represents its most clinically important spectrum:
Enterobacteriaceae
- Escherichia coli (including ESBL-producing strains) 3, 1
- Klebsiella pneumoniae (including ESBL-producing strains) 3, 1
- Proteus mirabilis 1
- Enterobacter cloacae (including AmpC-hyperproducers) 3, 4
- Serratia marcescens (including AmpC-hyperproducers) 5, 1
- Citrobacter species (including AmpC-hyperproducers) 5, 4
- Morganella morganii 1
- Proteus vulgaris 1
The Infectious Diseases Society of America specifically recommends meropenem for treating infections caused by Gram-negative bacilli that produce extended-spectrum β-lactamases or those that may hyperproduce lactamases (Enterobacter, Citrobacter, or Serratia species). 3
Non-Fermenting Gram-Negatives
- Pseudomonas aeruginosa (with maintained activity against many resistant strains) 5, 1, 4
- Acinetobacter baumannii 3
- Haemophilus influenzae 1, 4
- Moraxella catarrhalis 1
- Neisseria meningitidis 1
Meropenem demonstrates 4-fold to 32-fold lower MIC90 values against most Enterobacteriaceae and H. influenzae compared to other carbapenems, indicating superior potency. 4
Gram-Positive Coverage
Meropenem covers clinically important Gram-positive pathogens, though this is not its primary indication:
- Streptococcus pneumoniae (penicillin-susceptible isolates) 1
- Streptococcus pyogenes 1
- Streptococcus agalactiae 1
- Viridans group streptococci 1
- Enterococcus faecalis (vancomycin-susceptible isolates only) 1
- Staphylococcus aureus (methicillin-susceptible isolates only) 1, 6
Critical limitation: Meropenem has NO activity against methicillin-resistant Staphylococcus aureus (MRSA) or methicillin-resistant Staphylococcus epidermidis (MRSE). 1, 6
Anaerobic Coverage
Meropenem provides comprehensive anaerobic coverage, which distinguishes it from many other broad-spectrum agents and eliminates the need for metronidazole when carbapenems are used. 5
- Bacteroides fragilis 1
- Bacteroides thetaiotaomicron 1
- Peptostreptococcus species 1, 4
- Clostridium perfringens 1
- Clostridium difficile 1
- Fusobacterium species 1
- Prevotella species 1
- Propionibacterium acnes 1
Clinical Applications Based on Coverage
Preferred Scenarios for Meropenem
The IDSA recommends meropenem over piperacillin-tazobactam for high-risk scenarios including: 3
- Critically ill patients with sepsis or septic shock
- Known colonization with ESBL-producing Enterobacteriaceae
- Recent antibiotic exposure
- Healthcare-associated bloodstream infections
- Neutropenic patients
- ESBL-producing Klebsiella pneumoniae or Escherichia coli
- AmpC-hyperproducing organisms
- Any Gram-negative rod with documented resistance to third-generation cephalosporins
Hospital-Acquired and Ventilator-Associated Pneumonia
Meropenem is recommended for empiric therapy in patients with risk factors for multidrug-resistant pathogens, providing coverage against P. aeruginosa, Acinetobacter species, and ESBL-producing Enterobacteriaceae. 5
Intra-Abdominal Infections
Meropenem monotherapy provides adequate coverage for polymicrobial intra-abdominal infections without requiring additional anaerobic coverage, as it inherently covers both aerobic Gram-negatives and anaerobes. 5, 2
Febrile Neutropenia
Meropenem monotherapy is appropriate for high-risk febrile neutropenia, providing coverage against viridans group streptococci and Pseudomonas aeruginosa. 5, 2
Resistance Patterns and Limitations
Carbapenem Resistance
For carbapenem-resistant Gram-negative bacilli (CRGNB), standard meropenem is NOT effective. 3
- Newer formulations like meropenem-vaborbactam are recommended for severe infections due to carbapenem-resistant Enterobacteriaceae (CRE) if active in vitro 5, 3
- Meropenem-vaborbactam demonstrates activity against KPC-producing strains but retains no activity against OXA-48 producing strains 5
- For metallo-β-lactamase producers, alternative agents like cefiderocol or combination therapies are needed 3
Cross-Resistance Considerations
Imipenem shows high cross-resistance (87.9%) against meropenem-resistant P. aeruginosa, but meropenem shows lower cross-resistance (49.2%) against imipenem-resistant P. aeruginosa. 4
Common Pitfalls to Avoid
Relying on piperacillin-tazobactam for ESBL-producing organisms despite in vitro susceptibility can result in treatment failure rates of 20-40%, even when organisms appear susceptible. 3 This represents a critical clinical error that meropenem avoids.
Do not use meropenem empirically for suspected MRSA infections—vancomycin or alternative anti-MRSA agents must be added. 1
In settings with high carbapenem resistance rates, carbapenem-sparing strategies should be employed when appropriate to prevent further selection pressure for carbapenemase-producing strains. 5