Ceftriaxone Has Broader Spectrum Coverage Than Cefazolin
Ceftriaxone (Rocephin) has significantly broader spectrum coverage compared to cefazolin (Ancef), particularly against gram-negative organisms, making it more suitable for empiric treatment of serious infections where extended coverage is needed. 1, 2
Comparative Antimicrobial Spectrum
Ceftriaxone (Third-Generation Cephalosporin)
- Provides excellent coverage against most gram-negative aerobic bacilli including Escherichia coli, Proteus species, Klebsiella species, Morganella morganii, and many Enterobacteriaceae 3
- Maintains good activity against common gram-positive organisms including Streptococcus pneumoniae and Staphylococcus aureus (methicillin-susceptible) 1
- Has outstanding bactericidal action against pneumococci, group B streptococci, meningococci, gonococci, and Haemophilus influenzae 3
- Effective against Neisseria meningitidis and many strains of Bacteroides fragilis 1
- Demonstrates activity against some anaerobic bacteria 2
Cefazolin (First-Generation Cephalosporin)
- Provides good coverage against gram-positive organisms including Staphylococcus aureus (including beta-lactamase-producing strains) and Streptococcus species 4
- Has limited activity against gram-negative organisms, primarily covering Escherichia coli and Proteus mirabilis 4
- Most strains of Enterobacter species, Morganella morganii, Providencia, Serratia, and Pseudomonas species are resistant to cefazolin 4
- Has no significant activity against anaerobes 4
Clinical Applications Reflecting Spectrum Differences
Ceftriaxone Preferred For:
- Meningitis (caused by H. influenzae, N. meningitidis, or S. pneumoniae) 1
- Intra-abdominal infections (as a second-choice option with metronidazole) 5
- Severe community-acquired infections 5
- Gonorrhea (including penicillinase-producing strains) 1
- Bacteremia/septicemia caused by susceptible gram-negative organisms 1
Cefazolin Preferred For:
- Surgical prophylaxis 4
- Skin and soft tissue infections caused by susceptible gram-positive organisms 4
- MSSA (methicillin-susceptible S. aureus) infections, where it is considered superior to ceftriaxone 6
Evidence-Based Comparison
- Ceftriaxone has retained potent activity against the most commonly encountered gram-positive and gram-negative pathogens despite widespread clinical use for over 15 years 7
- The Surgical Infection Society and Infectious Diseases Society of America guidelines list ceftriaxone (with metronidazole) as a recommended combination therapy for intra-abdominal infections, while cefazolin is listed as a narrower-spectrum option 5
- For mild to moderate intra-abdominal infections, cefazolin plus metronidazole is considered a reasonable option with narrower spectrum than ceftriaxone 5
- The Infectious Diseases Society of America recommends cefazolin over ceftriaxone specifically for MSSA infections 6
Clinical Implications
- Ceftriaxone's broader spectrum makes it more appropriate for empiric therapy of serious infections when the causative organism is unknown 2
- Ceftriaxone's long half-life (5.8-8.7 hours) allows for once-daily dosing, which is a significant advantage over cefazolin's shorter half-life (approximately 1.8 hours) 3, 4
- The broader spectrum of ceftriaxone comes with increased risk of promoting antimicrobial resistance and potential for collateral damage to normal flora 5
- Cefazolin should be preferred when narrower spectrum is adequate, particularly for MSSA infections 6
Common Pitfalls and Caveats
- Using ceftriaxone when narrower-spectrum agents would be sufficient may contribute to antimicrobial resistance 5
- Ceftriaxone should not be used as sole therapy for Pseudomonas aeruginosa infections despite having some activity against this organism 2
- Neither cefazolin nor ceftriaxone provides adequate coverage against methicillin-resistant Staphylococcus aureus (MRSA) 4, 1
- For MSSA infections, cefazolin is generally preferred over ceftriaxone despite ceftriaxone's broader overall spectrum 6