From the Guidelines
Cefazolin and metronidazole (Flagyl) together provide adequate coverage for Group B Streptococcus (GBS), but cefazolin alone is sufficient for GBS treatment. Cefazolin, a first-generation cephalosporin, is highly effective against GBS as this organism remains universally susceptible to beta-lactam antibiotics 1. Metronidazole, while excellent for anaerobic coverage, does not contribute to GBS treatment specifically. For GBS infections, cefazolin alone at standard dosing (typically 1-2g IV every 8 hours for adults) is sufficient.
The key points to consider are:
- Cefazolin is recommended for women allergic to penicillin who are at low risk of anaphylaxis 1
- For women allergic to penicillin who are at high risk of anaphylaxis, clindamycin should be administered to those colonized with GBS that is known to be susceptible to clindamycin, or vancomycin for those with clindamycin-resistant GBS isolates 1
- The effectiveness of cefazolin against GBS is due to its mechanism of inhibiting cell wall synthesis in gram-positive bacteria
- Cefazolin and metronidazole combination is commonly used in surgical prophylaxis or intra-abdominal infections where both gram-positive coverage (including GBS) and anaerobic coverage are needed
It's worth noting that the most recent guidelines from 2020 recommend cefazolin for women allergic to penicillin who are at low risk of anaphylaxis, and clindamycin or vancomycin for those at high risk of anaphylaxis, depending on the susceptibility of the GBS isolate 1.
From the Research
Antibiotic Coverage for Group B Streptococcus
- Cefazolin is effective against Group B Streptococcus (GBS), as all isolates were susceptible to cefazolin in the studies 2, 3, 4, 5.
- Flagyl (metronidazole) is not typically used for GBS coverage, as it is not effective against this type of bacteria.
- The combination of cefazolin and Flagyl may not provide adequate coverage for GBS, as Flagyl is not effective against GBS.
- Alternative antibiotics, such as clindamycin or vancomycin, may be used in patients with penicillin allergy, but cefazolin is a suitable option for patients without anaphylaxis 6, 5.
- The use of cefazolin for GBS prophylaxis in women reporting a penicillin allergy without anaphylaxis is supported by studies 5.
- Antibiotic susceptibility testing is important to determine the effectiveness of antibiotics against GBS isolates 2, 6, 3, 4.
Group B Streptococcus Susceptibility
- GBS isolates are generally susceptible to penicillin, ampicillin, and cefazolin 2, 3, 4.
- Resistance to erythromycin and clindamycin has been reported, but cefazolin remains effective 2, 3, 4.
- The use of cefazolin and Flagyl may not be the best option for GBS coverage, as Flagyl is not effective against GBS.
Clinical Implications
- Cefazolin is a suitable option for GBS prophylaxis in patients without anaphylaxis 5.
- Antibiotic susceptibility testing is crucial to determine the effectiveness of antibiotics against GBS isolates 2, 6, 3, 4.
- The combination of cefazolin and Flagyl may not provide adequate coverage for GBS, and alternative antibiotics should be considered 6, 5.