What bacteria do antibiotics such as amoxicillin-clavulanate (Augmentin), ceftriaxone (Rocephin), and levofloxacin (Levaquin) cover and not cover?

Antibiotic Coverage Comparison: Amoxicillin-Clavulanate, Ceftriaxone, and Levofloxacin

Amoxicillin-clavulanate (Augmentin), ceftriaxone (Rocephin), and levofloxacin (Levaquin) each have distinct antimicrobial coverage profiles, with levofloxacin offering the broadest spectrum of activity against both gram-positive and gram-negative pathogens including atypical organisms.

Amoxicillin-Clavulanate (Augmentin)

Covers:

• Gram-positive organisms:

  • Streptococcus pneumoniae (including many penicillin-resistant strains)
  • Streptococcus species
  • Staphylococcus aureus (methicillin-susceptible)
  • Enterococcus faecalis

• Gram-negative organisms:

  • Haemophilus influenzae (including β-lactamase producing strains)
  • Moraxella catarrhalis (including β-lactamase producing strains)
  • Escherichia coli
  • Klebsiella species
  • Proteus mirabilis

• Anaerobes:

  • Many Bacteroides species
  • Peptostreptococcus species
  • Clostridium species

Does not cover:

• Methicillin-resistant Staphylococcus aureus (MRSA)
• Pseudomonas aeruginosa
• Atypical pathogens (Mycoplasma, Chlamydophila, Legionella)
• Enterobacter species (often resistant)
• Extended-spectrum β-lactamase (ESBL) producing organisms
• Enterococcus faecium

Ceftriaxone (Rocephin)

Covers:

• Gram-positive organisms:

  • Streptococcus pneumoniae (including many penicillin-resistant strains)
  • Streptococcus species
  • Staphylococcus aureus (methicillin-susceptible)

• Gram-negative organisms:

  • Haemophilus influenzae
  • Moraxella catarrhalis
  • Escherichia coli
  • Klebsiella species
  • Proteus species
  • Serratia marcescens
  • Enterobacter species (variable)
  • Neisseria gonorrhoeae

• Limited anaerobic coverage

Does not cover:

• Methicillin-resistant Staphylococcus aureus (MRSA)
• Pseudomonas aeruginosa (limited activity)
• Atypical pathogens (Mycoplasma, Chlamydophila, Legionella)
• Enterococcus species
• ESBL-producing organisms
• Most anaerobes (particularly Bacteroides fragilis)

Levofloxacin (Levaquin)

Covers:

• Gram-positive organisms:

  • Streptococcus pneumoniae (including multi-drug resistant strains)
  • Staphylococcus aureus (methicillin-susceptible)
  • Staphylococcus epidermidis (methicillin-susceptible)
  • Streptococcus pyogenes
  • Enterococcus faecalis

• Gram-negative organisms:

  • Haemophilus influenzae
  • Haemophilus parainfluenzae
  • Moraxella catarrhalis
  • Escherichia coli
  • Klebsiella pneumoniae
  • Proteus mirabilis
  • Pseudomonas aeruginosa (variable)
  • Legionella pneumophila
  • Enterobacter cloacae
  • Serratia marcescens

• Atypical pathogens:

  • Chlamydophila pneumoniae
  • Mycoplasma pneumoniae

Does not cover:

• Methicillin-resistant Staphylococcus aureus (MRSA) - variable activity
• Most anaerobes (particularly Bacteroides fragilis)
• Some ESBL-producing organisms
• Enterococcus faecium (variable)

Key Clinical Considerations

1. For respiratory infections:

   • Levofloxacin provides the most comprehensive coverage including atypical pathogens 1, 2
   • Amoxicillin-clavulanate is effective against common respiratory pathogens but lacks atypical coverage 3
   • Ceftriaxone has good activity against S. pneumoniae but requires combination therapy for atypical coverage 4

2. For skin and soft tissue infections:

   • Amoxicillin-clavulanate is appropriate for mild-moderate infections 1
   • Ceftriaxone with metronidazole provides broader coverage for moderate-severe infections 1
   • Levofloxacin is effective but should be reserved due to resistance concerns 1

3. For intra-abdominal infections:

   • Amoxicillin-clavulanate is recommended for mild-moderate community-acquired infections 1
   • Ceftriaxone plus metronidazole is appropriate for severe infections 1
   • Levofloxacin plus metronidazole is a second-choice option 1

4. For diabetic foot infections:

   • Amoxicillin-clavulanate for mild infections without MRSA risk 1
   • Levofloxacin for moderate infections or when broader coverage is needed 1
   • Ceftriaxone for parenteral therapy in moderate-severe infections 1

Resistance Considerations

• Increasing prevalence of fluoroquinolone resistance limits empiric use of levofloxacin in some settings 1
• ESBL-producing organisms are resistant to amoxicillin-clavulanate and often to ceftriaxone 1
• Penicillin-resistant S. pneumoniae may require high-dose amoxicillin-clavulanate 3
• Local resistance patterns should guide empiric therapy choices

Common Pitfalls to Avoid

1. Using levofloxacin as first-line therapy for uncomplicated infections (increases resistance risk)
2. Failing to add anaerobic coverage (metronidazole) when using ceftriaxone for mixed infections
3. Relying on amoxicillin-clavulanate for suspected Pseudomonas infections
4. Using ceftriaxone alone for suspected MRSA infections
5. Not considering local resistance patterns when selecting empiric therapy

Remember that antibiotic selection should be guided by the suspected pathogens, site of infection, local resistance patterns, and patient-specific factors such as allergies and comorbidities.