From the Guidelines
Metronidazole is an antibiotic that primarily covers anaerobic bacterial infections and certain protozoal infections, including Giardia lamblia, Entamoeba histolytica, Trichomonas vaginalis, and Clostridium difficile. It is effective against most anaerobic bacteria including Bacteroides fragilis, Clostridium species, Fusobacterium, Peptostreptococcus, and Prevotella 1. For protozoal infections, metronidazole treats Giardia lamblia, Entamoeba histolytica, and Trichomonas vaginalis, as well as being used for bacterial vaginosis caused by Gardnerella vaginalis and as part of combination therapy for Helicobacter pylori infections 1. Some common clinical applications include:
- Intra-abdominal infections
- Pelvic inflammatory disease
- Brain abscesses
- Diabetic foot infections
- Clostridium difficile colitis
- Dental infections Metronidazole works by entering bacterial cells and being reduced by bacterial enzymes into reactive compounds that damage bacterial DNA, making it particularly effective against organisms that thrive in low-oxygen environments 1. The drug cannot be used for aerobic infections as it requires the reducing environment found in anaerobic organisms to become activated. In the context of the provided guidelines, metronidazole is still acceptable treatment for nonsevere Clostridium difficile infection (CDI) in children and as a second-line agent for adults with nonsevere CDI 1. Additionally, metronidazole is used to treat trichomoniasis, with cure rates of approximately 95% in randomized clinical trials 1. It is also used to treat bacterial vaginosis, with recommended regimens including 500 mg orally twice daily for 7 days or metronidazole gel 0.75% intravaginally once daily for 5 days 1.
From the FDA Drug Label
Metronidazole tablets are indicated for the treatment of symptomatic trichomoniasis in females and males when the presence of the trichomonad has been confirmed by appropriate laboratory procedures Metronidazole tablets are indicated in the treatment of acute intestinal amebiasis (amebic dysentery) and amebic liver abscess Metronidazole tablets are indicated in the treatment of serious infections caused by susceptible anaerobic bacteria INTRA‑ABDOMINAL INFECTIONS, including peritonitis, intra‑abdominal abscess, and liver abscess, caused by Bacteroides species including the B. fragilis group SKIN AND SKIN STRUCTURE INFECTIONS caused by Bacteroides species including the B. fragilis group, Clostridium species, Peptococcus niger, Peptostreptococcus species, and Fusobacterium species GYNECOLOGIC INFECTIONS, including endometritis, endomyometritis, tubo‑ovarian abscess, and postsurgical vaginal cuff infection, caused by Bacteroides species including the B. fragilis group, Clostridium species, Peptococcusniger, and Peptostreptococcus species BACTERIAL SEPTICEMIA caused by Bacteroides species including the B. fragilis group, and Clostridium species BONE AND JOINT INFECTIONS, as adjunctive therapy, caused by Bacteroides species including the B. fragilis group CENTRAL NERVOUS SYSTEM (CNS) INFECTIONS, including meningitis and brain abscess, caused by Bacteroides species including the B. fragilis group LOWER RESPIRATORY TRACT INFECTIONS, including pneumonia, empyema, and lung abscess, caused by Bacteroides species including the B fragilis group ENDOCARDITIS caused by Bacteroides species including the B. fragilis group
Metronidazole covers infections caused by:
- Trichomoniasis
- Amebiasis (acute intestinal and liver abscess)
- Anaerobic bacterial infections, including:
- Intra-abdominal infections
- Skin and skin structure infections
- Gynecologic infections
- Bacterial septicemia
- Bone and joint infections
- Central nervous system infections
- Lower respiratory tract infections
- Endocarditis 2
From the Research
Metronidazole Coverage
Metronidazole is a 5-nitroimidazole that has selective activity against anaerobic microorganisms, including bacteria and protozoa 3. The spectrum of activity of metronidazole encompasses:
- Almost all anaerobic bacteria
- Some capnophilic organisms
- Protozoans like Entamoeba histolytica, Giardia lamblia, and Trichomonas vaginalis 4
- Anaerobic bowel flora, used for prophylaxis and treatment of patients with Crohn's disease 4
- Helicobacter pylori, usually with acid suppression medication plus bismuth and amoxicillin 4
- Clostridium difficile-induced pseudomembraneous colitis 4
- Bacteroides species, fusobacteria, and clostridia 5
- Gardnerella vaginalis 5
- Trichomoniasis, amoebiasis, and giardiasis 5
Infections Treated by Metronidazole
Metronidazole is used to treat various infections, including:
- Anaerobic bacterial infections
- Trichomonal vaginitis
- Bacterial vaginosis
- Amoebiasis
- Giardiasis
- Intraabdominal sepsis
- Pelvic suppuration
- Necrotizing soft tissue infections
- Anaerobic brain abscesses
- Vaginosis due to Gardnerella vaginalis
- Gastroduodenal ulcers caused by Helicobacter pylori 3, 4, 5, 6, 7
Resistance to Metronidazole
Rates of resistance to metronidazole are generally low, but several studies have reported decreased susceptibility among Bacteroides species, as well as different mechanisms of resistance 5. Metronidazole-resistant Helicobacter pylori strains have been described, but combination therapy is still recommended for eradication of this pathogen in patients with gastroduodenal ulcers 5.