Is cefazolin (Cefazolin) or cephalexin (Cephalexin) more broad-spectrum?

From the Guidelines

Cefazolin is more broad-spectrum than cephalexin due to its enhanced activity against certain gram-negative bacteria, including Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis, as supported by the Infectious Diseases Society of America guidelines 1.

Key Points

• Both cefazolin and cephalexin are first-generation cephalosporin antibiotics, but they differ in their antimicrobial coverage.
• Cefazolin has better coverage against gram-negative bacteria, making it more broad-spectrum than cephalexin.
• The Infectious Diseases Society of America guidelines recommend cefazolin for purulent skin and soft tissue infections, as well as for incisional surgical site infections after surgery of the trunk or an extremity away from axilla or perineum 1.

Clinical Applications

• Cefazolin is particularly useful for surgical prophylaxis and treatment of more complex infections due to its broader coverage.
• However, cefazolin is only available as an injectable formulation (IV or IM), while cephalexin is administered orally, which influences their clinical applications.
• Neither antibiotic is effective against extended-spectrum beta-lactamase (ESBL) producing organisms, Pseudomonas, Enterobacter, methicillin-resistant Staphylococcus aureus (MRSA), or anaerobes.

Mechanism of Action

• The broader spectrum of cefazolin comes from its molecular structure, which allows better penetration of the outer membrane of gram-negative bacteria and greater stability against certain beta-lactamases.
• This mechanism of action makes cefazolin a more effective option for treating infections caused by gram-negative bacteria, as supported by the study by Kilburn SA (2010) 1, which compared different interventions for cellulitis and found that cephalosporins, including cefazolin, were effective against gram-negative bacteria.

From the Research

Comparison of Cefazolin and Cephalexin

• Cefazolin and cephalexin are both cephalosporin antibiotics, but they have different spectrums of activity 2.
• Cephalexin has an antimicrobial spectrum that includes pathogens most frequently encountered in clinical practice, such as upper and lower respiratory tract, skin and soft tissue, and genitourinary tract infections 3.
• Cefazolin is more active against gram-negative pathogens, including Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis, compared to cephalexin 2.
• Cefazolin is also more potent against Staphylococcus aureus, with more than 90% of strains suppressed by cefazolin at concentrations of 3.13 μg/ml or less, compared to 49.1% for cephalexin 2.

Broad-Spectrum Activity

• Cefazolin has a broader spectrum of activity against gram-negative bacteria, making it a more broad-spectrum antibiotic compared to cephalexin 2.
• Cephalexin, on the other hand, is more effective against gram-positive bacteria and is commonly used to treat infections such as skin and soft tissue infections, and urinary tract infections 3, 4.
• The selection of cefazolin or cephalexin depends on the specific infection being treated and the suspected or confirmed causative pathogens 5, 4.

Clinical Use

• Cefazolin is often used as a first-line treatment for serious bacterial infections, including skin and soft tissue infections, and urinary tract infections 2, 5.
• Cephalexin is also commonly used to treat urinary tract infections, particularly in the era of "bad bugs, few drugs", where there are limited oral options against resistant Enterobacteriaceae 4.
• Both cefazolin and cephalexin can be effective treatment options, but the choice of antibiotic depends on the specific clinical scenario and the patient's individual needs 5, 4.