Is ceftazidime (a third-generation cephalosporin antibiotic) more broad-spectrum than ceftriaxone (a third-generation cephalosporin antibiotic)?

Comparison of Ceftazidime and Ceftriaxone Spectrum of Activity

Ceftazidime has a broader spectrum of activity than ceftriaxone specifically due to its superior activity against Pseudomonas aeruginosa, while ceftriaxone has better coverage against certain Gram-positive organisms and anaerobes. 1, 2

Spectrum of Activity Comparison

Ceftazidime

• Gram-negative coverage:

  • Excellent activity against Gram-negative bacteria including Enterobacteriaceae 3
  • Superior activity against Pseudomonas aeruginosa (approximately 4 times more active than ceftriaxone) 2
  • Active against beta-lactamase producing strains 4

• Gram-positive coverage:

  • Less active against Staphylococcus aureus compared to first and second generation cephalosporins 4
  • Limited activity against many Gram-positive organisms 1

• Anaerobic coverage:

  • Poor activity against Bacteroides fragilis group (MIC90 >128 mg/L) 2

Ceftriaxone

• Gram-negative coverage:

  • Good activity against Enterobacteriaceae 5
  • Some activity against Pseudomonas aeruginosa but insufficient for monotherapy 5
  • Active against Haemophilus influenzae and Neisseria meningitidis 6

• Gram-positive coverage:

  • Better activity against Gram-positive organisms than ceftazidime 5
  • Active against Streptococcus pneumoniae 6

• Anaerobic coverage:

  • Limited but better than ceftazidime against Bacteroides fragilis (MIC90 32 mg/L) 2

Clinical Applications Based on Spectrum Differences

When to Choose Ceftazidime

• Infections where Pseudomonas aeruginosa is suspected or confirmed 3, 1
• Empiric therapy for nosocomial infections in settings with high Pseudomonas prevalence 1
• Cystic fibrosis patients with respiratory infections 4
• Severe hospital-acquired pneumonia where Pseudomonas coverage is needed 3

When to Choose Ceftriaxone

• Community-acquired pneumonia 3
• Meningitis 6
• Intra-abdominal infections without suspected Pseudomonas 3
• Gonorrhea and other sexually transmitted infections 6
• Skin and soft tissue infections without Pseudomonas risk 6

Important Clinical Considerations

• Resistance concerns: Both antibiotics can select for resistant organisms with prolonged use 3
• Dosing advantage: Ceftriaxone has a longer half-life allowing once-daily dosing, while ceftazidime typically requires multiple daily doses 7
• Cost-effectiveness: The once-daily dosing of ceftriaxone often makes it more cost-effective than ceftazidime 7

Common Pitfalls to Avoid

1. Assuming broader spectrum means better: While ceftazidime has broader Gram-negative coverage due to its anti-pseudomonal activity, this doesn't make it the better choice for all infections. Choose based on the suspected pathogens.

2. Monotherapy for polymicrobial infections: For intra-abdominal infections, neither ceftazidime nor ceftriaxone provides adequate anaerobic coverage alone and should be combined with metronidazole 3.

3. Overusing broad-spectrum agents: Using ceftazidime when Pseudomonas is unlikely contributes to antimicrobial resistance. Reserve it for appropriate indications 3.

4. Inadequate dosing: For serious Pseudomonas infections, appropriate dosing of ceftazidime is critical for efficacy and to prevent resistance development 3.

In summary, while ceftazidime has broader Gram-negative coverage primarily due to its superior anti-pseudomonal activity, ceftriaxone has advantages in certain clinical scenarios due to its better Gram-positive coverage, once-daily dosing, and cost-effectiveness.