From the Guidelines
Augmentin does not reliably cover Bacteroides fragilis, and its use is not recommended for infections where coverage of this organism is necessary. According to the guidelines for the diagnosis and management of complicated intra-abdominal infection in adults and children, published in the Clinical Infectious Diseases journal 1, coverage for obligate anaerobic bacilli, including B. fragilis, should be provided for distal small bowel, appendiceal, and colon-derived infections. The guidelines also mention that cefotetan and clindamycin are not recommended for use because of increasing prevalence of resistance to these agents among the B. fragilis group (B-II) 1.
Some key points to consider when choosing an antibiotic for B. fragilis coverage include:
- The use of ticarcillin-clavulanate, cefoxitin, ertapenem, moxifloxacin, or tigecycline as single-agent therapy or combinations of metronidazole with cefazolin, cefuroxime, ceftriaxone, cefotaxime, levofloxacin, or ciprofloxacin are preferable to regimens with substantial anti-Pseudomonal activity 1
- Increasing antimicrobial resistance among B. fragilis isolates is of concern, and there are data indicating higher failure rates if these organisms are treated with an inactive agent 1
- Antimicrobial selection should be based on local microbiologic data, cost advantage, allergies, and formulary availability 1
For infections where B. fragilis coverage is needed, such as intra-abdominal infections, perforated appendicitis, or diabetic foot infections, more appropriate antibiotic choices would include metronidazole, carbapenems (like meropenem or ertapenem), or combination therapies, as recommended by the guidelines 1.
From the Research
Antibiotic Coverage of Bacteroides Fragilis
- Bacteroides fragilis is a common anaerobic bacteria that can cause infections, and it is highly resistant to many antibiotics 2.
- The antibiotic resistance pattern of B. fragilis has been studied, and it has been found that the bacteria is highly resistant to penicillin G, tetracycline, clindamycin, and cefoxitin 2.
- However, B. fragilis is susceptible to metronidazole, and this antibiotic is often used as a first-line treatment for infections caused by this bacteria 2.
- Amoxicillin/clavulanic acid (Augmentin) has been shown to be effective against B. fragilis in some studies, particularly in mixed infections with other bacteria such as Escherichia coli 3.
- The efficacy of Augmentin against B. fragilis has been demonstrated in experimental mixed infections, where it was able to prevent the development of infection and eliminate both B. fragilis and E. coli 3.
Susceptibility of Bacteroides Fragilis to Augmentin
- The susceptibility of B. fragilis to Augmentin has been evaluated in several studies, and the results have shown that the bacteria is generally susceptible to this antibiotic 3, 4, 5.
- However, the resistance rate of B. fragilis to Augmentin has been increasing over the years, and it is now around 10% in some European countries 4.
- Piperacillin/tazobactam has been shown to be more active than Augmentin against B. fragilis, with a lower resistance rate of around 3% 4.
- The susceptibility of B. fragilis to Augmentin can vary depending on the geographical location, with higher resistance rates observed in some Scandinavian countries 4.
Clinical Implications
- The use of Augmentin against B. fragilis infections should be guided by susceptibility testing and clinical experience 3, 4, 5.
- The increasing resistance rate of B. fragilis to Augmentin highlights the need for continued monitoring of susceptibility patterns and the development of new antibiotics 4.
- Metronidazole remains a highly effective antibiotic against B. fragilis, with no resistance detected in many studies 2, 5.