From the Guidelines
For anaerobic and gas-producing infections, when already using vancomycin and piperacillin-tazobactam (Zosyn), consider adding metronidazole (Flagyl) 500 mg IV every 8 hours or clindamycin 600-900 mg IV every 8 hours. While Zosyn already provides good anaerobic coverage, adding metronidazole can enhance anaerobic activity, particularly for severe infections like necrotizing fasciitis or gas gangrene, as suggested by the guidelines for the diagnosis and management of skin and soft tissue infections 1. Clindamycin offers the additional benefit of toxin suppression in toxin-producing infections like those caused by Clostridium species. For severe infections, consider adding meropenem 1 gram IV every 8 hours instead, which provides excellent broad-spectrum coverage including anaerobes.
Some key points to consider when managing these infections include:
- The importance of prompt surgical consultation for patients with aggressive infections associated with signs of systemic toxicity or suspicion of necrotizing fasciitis or gas gangrene 1
- The need for empiric antibiotic treatment to be broad, covering both aerobes and anaerobes, as the etiology can be polymicrobial or monomicrobial 1
- The role of clindamycin in treating necrotizing fasciitis and/or streptococcal toxic shock syndrome caused by group A streptococci, due to its ability to suppress toxin production and modulate cytokine production 1
Duration of treatment typically ranges from 7-14 days depending on clinical response, with longer courses for deep tissue infections. It is essential to remember that surgical debridement remains crucial for gas-forming infections, as antibiotics alone are often insufficient. Monitoring for antibiotic-associated complications, including C. difficile infection, is also vital, especially when using multiple broad-spectrum agents.
From the FDA Drug Label
In the treatment of most serious anaerobic infections, the intravenous form of metronidazole is usually administered initially. The usual adult oral dosage is 7. 5 mg/kg every six hours (approx. 500 mg for a 70 kg adult). A maximum of 4 g should not be exceeded during a 24 hour period. The usual duration of therapy is 7 to 10 days; however, infections of the bone and joint, lower respiratory tract, and endocardium may require longer treatment
Metronidazole can be a good antibiotic choice to add to vancomycin and Zosyn (piperacillin/tazobactam) to cover for anaerobic and gas-producing infections.
- The recommended dosage is 7.5 mg/kg every six hours, approximately 500 mg for a 70 kg adult.
- The maximum dose should not exceed 4 g in a 24-hour period.
- The usual duration of therapy is 7 to 10 days, but may be longer for certain infections 2.
From the Research
Antibiotic Choices for Anaerobic and Gas Producing Infections
To cover for anaerobic and gas producing infections, the following antibiotics can be considered in addition to vancomycin (Vanc) and piperacillin-tazobactam (Zosyn):
- Metronidazole, as it has selective activity against anaerobic microorganisms, including bacteria and protozoa 3, 4, 5, 6
- Clindamycin, which may be necessary for serious infections, especially those involving Bacteroides fragilis 7
- Cefoxitin sodium, which is adequate for most anaerobic infections occurring outside the central nervous system 7
- Chloramphenicol, imipenem, or beta-lactam antibiotics combined with beta-lactamase inhibitors, which may be preferable for serious infections 7
Considerations for Treatment
When treating anaerobic infections, it is essential to:
- Include appropriate coverage for aerobic bacteria in the treatment regimen 3, 7
- Consider the site and severity of the infection, as well as the presence of any underlying conditions or predisposing factors 7
- Drain abscesses, decompress infected spaces, debride necrotic tissue, and remove foreign bodies as necessary 7