Do Rocephin (Ceftriaxone) and Keflex (Cephalexin) cover the same spectrum of bacteria?

Rocephin (Ceftriaxone) and Keflex (Cephalexin) Antimicrobial Coverage Comparison

No, Rocephin (ceftriaxone) and Keflex (cephalexin) do not cover the same spectrum of bacteria. Ceftriaxone is a third-generation cephalosporin with broader gram-negative coverage, while cephalexin is a first-generation cephalosporin with better gram-positive but limited gram-negative coverage.

Key Differences in Antimicrobial Coverage

Ceftriaxone (Rocephin) Coverage

• Broader gram-negative coverage including:

  • Excellent activity against Haemophilus influenzae 1
  • Effective against Neisseria gonorrhoeae (including penicillinase-producing strains) 1
  • Active against many Enterobacteriaceae including E. coli, Klebsiella, Proteus species 2
  • Some activity against Pseudomonas aeruginosa (though not recommended as monotherapy) 2, 3
  • Effective against Moraxella catarrhalis 2

• Gram-positive coverage:

  • Active against Streptococcus pneumoniae including some penicillin-resistant strains 1
  • Less active against Staphylococcus aureus compared to first-generation cephalosporins 3

• Other characteristics:

  • Parenteral administration only (IV/IM) 2
  • Long half-life allowing once-daily dosing 2, 4
  • Penetrates CSF in the presence of inflamed meninges 2

Cephalexin (Keflex) Coverage

• Strong gram-positive coverage including:

  • Very effective against Staphylococcus aureus (including penicillinase-producing strains) 5, 6
  • Active against Streptococcus pneumoniae (penicillin-susceptible strains only) 5
  • Active against Streptococcus pyogenes 5

• Limited gram-negative coverage:

  • Active against some E. coli strains 5, 7
  • Some activity against Klebsiella pneumoniae 5, 7
  • Active against Proteus mirabilis 5
  • Limited activity against Haemophilus influenzae 5
  • No activity against Pseudomonas species 5

• Other characteristics:

  • Oral administration only 5, 6
  • Shorter half-life requiring multiple daily doses 6
  • Does not penetrate CSF effectively 6

Clinical Implications of Different Coverage

When to Use Ceftriaxone

• Severe infections requiring broader gram-negative coverage 1
• Meningitis due to its CSF penetration 2
• Gonorrhea treatment (single dose effective) 1
• Moderate to severe community-acquired infections 1
• Healthcare-associated infections when combined with other agents 1

When to Use Cephalexin

• Mild to moderate skin and soft tissue infections 1
• Uncomplicated urinary tract infections 6
• Upper respiratory tract infections caused by susceptible organisms 6
• Outpatient treatment of infections caused by susceptible gram-positive organisms 6

Common Pitfalls and Caveats

• Do not substitute cephalexin for ceftriaxone in severe infections requiring broad gram-negative coverage 1, 3
• Ceftriaxone requires parenteral administration while cephalexin is only available orally 2, 5
• Cross-reactivity in patients with penicillin allergy can occur with both agents 1
• Methicillin-resistant Staphylococcus aureus (MRSA) is resistant to both ceftriaxone and cephalexin 5
• Enterococcus faecalis is resistant to both agents 5
• Pseudomonas aeruginosa is not effectively covered by either agent as monotherapy 2, 5

Antimicrobial Stewardship Considerations

• Reserve ceftriaxone for more severe infections to prevent resistance development 1
• Use cephalexin for milder infections when gram-positive coverage is primarily needed 1, 6
• Consider local resistance patterns when selecting either agent 1
• Avoid unnecessary broad-spectrum coverage with ceftriaxone when narrower spectrum agents like cephalexin would be sufficient 1

In summary, these two cephalosporins have significantly different antimicrobial spectra, with ceftriaxone offering much broader gram-negative coverage while cephalexin provides good gram-positive coverage with more limited gram-negative activity.