From the Guidelines
Flagyl (metronidazole) does not effectively cover enterococci. Metronidazole is primarily active against anaerobic bacteria and certain protozoal infections, but enterococci are facultative anaerobes that are intrinsically resistant to this medication 1. For enterococcal infections, more appropriate antibiotic choices would include ampicillin or penicillin (for susceptible strains), or vancomycin for resistant strains. Often, combination therapy with an aminoglycoside like gentamicin is used for serious enterococcal infections to achieve synergistic killing. The reason for metronidazole's ineffectiveness against enterococci relates to its mechanism of action, which requires reduction of its nitro group within anaerobic organisms to form toxic metabolites that damage bacterial DNA. Enterococci lack the necessary reductive enzymes to activate metronidazole, allowing them to remain unaffected by the drug.
Some key points to consider when treating enterococcal infections include:
- Enterococci are relatively resistant to penicillin, ampicillin, and vancomycin, and require synergistic action with an aminoglycoside to achieve bactericidal activity 1.
- High-level resistance to gentamicin is a concern, and susceptibility testing is necessary to predict synergistic interactions 1.
- Local susceptibility patterns for enterococci should be monitored, and empiric antimicrobial therapy should be guided by these patterns 1.
- Combination therapy with an aminoglycoside like gentamicin is often used for serious enterococcal infections to achieve synergistic killing 1.
When treating suspected or confirmed enterococcal infections, it's essential to select antibiotics with proven activity against these organisms rather than relying on metronidazole. The most recent and highest quality study 1 supports the use of ampicillin, penicillin, or vancomycin, often in combination with an aminoglycoside, for the treatment of enterococcal infections.
From the Research
Antibiotic Coverage for Enterococci
- Flagyl, also known as metronidazole, is an antibiotic with a limited spectrum of activity that encompasses various protozoans and most Gram-negative and Gram-positive anaerobic bacteria 2.
- The studies provided do not specifically mention Flagyl as an effective treatment for enterococci, which are Gram-positive cocci 3, 4.
- Enterococci are typically treated with antibiotics such as ampicillin, vancomycin, linezolid, daptomycin, and tigecycline, which have unique safety profiles and side effects 4.
- Metronidazole has been used to treat anaerobic-related infections, including those caused by Gram-positive anaerobes such as peptostreptococci and Clostridia spp., but its effectiveness against enterococci is not well-established 2, 5.
Mechanism of Action and Resistance
- Metronidazole works by inhibiting the synthesis of DNA in microbial cells, but its mechanism of action against enterococci is not well-understood 2.
- Enterococci have developed resistance to several antibiotics, including vancomycin, which is a concern in the treatment of enterococcal infections 3, 4, 6.
- The use of synergistic combinations of antibiotics may be warranted in complex infections caused by enterococci, but monotherapies are generally appropriate for uncomplicated infections 3.