Carbapenems

Carbapenems: overview (quick reference table)

Carbapenems are a class of β-lactam antibiotics renowned for their broad spectrum of activity and their ability to combat many multi-drug resistant bacterial infections. Often considered the "last line of defense," these antibiotics are used in critical and severe infections where other treatments have failed.

Carbapenems work by inhibiting bacterial cell wall synthesis, making them highly effective against a wide range of Gram-positive, Gram-negative, and anaerobic bacteria. They are particularly valuable in treating hospital-acquired infections, including those caused by ESBL-producing organisms (extended-spectrum beta-lactamases), which are resistant to most other β-lactams.

1. Imipenem (not commonly used in clinical practice)

• Spectrum:
  • Gram-positive: MSSA, Streptococcus, Enterococcus faecalis (some activity)
  • Gram-negative: Broad, including Pseudomonas, Enterobacteriaceae
  • Anaerobes: Good anaerobic coverage
• Key Notes:
  • Used for mixed infections, including those with Pseudomonas and anaerobes.
  • Risk of seizures, especially in patients with renal impairment, due to higher neurotoxicity compared to other carbapenems.
  • Some activity against Enterococcus faecalis, but not VRE.

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2. Meropenem (commonly used in clinical practice)

• Spectrum:
  • Gram-positive: MSSA, Streptococcus, Enterococcus faecalis (limited)
  • Gram-negative: Broad, including Pseudomonas, Enterobacteriaceae
  • Anaerobes: Good anaerobic coverage
• Key Notes:
  • Similar to Imipenem, but with lower seizure risk, making it safer in patients with CNS disorders.
  • Commonly used empirically in severe infections, meningitis.
  • Reliable for Pseudomonas and Gram-negative organisms.

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3. Doripenem (less commonly used in clinical practice, copycat from Meropenem)

• Spectrum:
  • Gram-positive: MSSA, Streptococcus
  • Gram-negative: Broad, including Pseudomonas, Enterobacteriaceae
  • Anaerobes: Good anaerobic coverage
• Key Notes:
  • Has the strongest activity against Pseudomonas among the carbapenems.
  • Used in severe infections like hospital-acquired pneumonia and complicated intra-abdominal infections.
  • Not widely used due to competition with Meropenem and Imipenem, but useful in specific cases requiring strong Pseudomonas coverage.

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4. Ertapenem

• Spectrum:
  • Gram-positive: MSSA, Streptococcus
  • Gram-negative: Broad, but NO activity against Pseudomonas, Acinetobacter, or Enterococcus
  • Anaerobes: Good anaerobic coverage
• Key Notes:
  • Commonly used for ESBL infections 
  • Lacks Pseudomonas and Acinetobacter activity, making it less suitable for empirical use for severe or hospital-acquired infections.
  • Ideal for use in outpatient settings because of its once-daily dosing.

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Summary

• Imipenem: Broad-spectrum, covers Pseudomonas and anaerobes. Risk of seizures, especially in renal impairment. Some activity against Enterococcus faecalis.
• Meropenem: Broad-spectrum, lower seizure risk than Imipenem. Great for meningitis, sepsis, and intra-abdominal infections.
• Doripenem: Strongest Pseudomonas activity, excellent for severe infections like hospital-acquired pneumonia.
• Ertapenem: Lacks Pseudomonas, Acinetobacter, and Enterococcus coverage, but great for community-acquired infections with once-daily dosing.