Metronidazole has been shown to be active against most isolates of the following bacteria both in vitro and in clinical infections as described in the INDICATIONS AND USAGE section.
Bacteroides fragilis group (B. fragilis , B. distasonis , B. ovatus , B. thetaiotaomicron , B.vulgatus)
The following in vitro data are available, but their clinical significance is unknown:
Metronidazole exhibits in vitro minimal inhibitory concentrations (MIC’s) of 8 mcg/mL or less against most (≥ 90%) isolates of the following bacteria; however, the safety and effectiveness of metronidazole in treating clinical infections due to these bacteria have not been established in adequate and well-controlled clinical trials.
Bacteroides fragilis group (B. caccae , B. uniformis)
Prevotella species (P. bivia , P. buccae , P. disiens)
Susceptibility Tests: When available, the clinical microbiology laboratory should provide results of in vitro susceptibility test results for antimicrobial drug products used in resident hospitals to the physician as periodic reports that describe the susceptibility profile of nosocomial or community-acquired pathogens. These reports should aid the physician in selecting an antibacterial drug product for treatment.
Quantitative methods are used to determine antimicrobial inhibitory concentrations (MICs). These MICs provide estimates of the susceptibility of bacteria to antimicrobial compounds. For anaerobic bacteria, the susceptibility to metronidazole can be determined by the reference broth and/or agar method1,2.
The MIC values should be interpreted according to the criteria provided in the following Table
*Agar dilution method is recommended for all anaerobes
†Broth dilution method is recommended for testing of Bacteroides fragilis group only; for this group, MIC values by agar and broth dilution methods are considered equivalent
A report of Susceptible (S) indicates that the antimicrobial is likely to inhibit growth of the pathogen if the antimicrobial compound reaches the concentrations at the infection site necessary to inhibit growth of the pathogen. A report of Intermediate (I) implies that an infection due to the isolate may be appropriately treated in the body sites where the drugs are physiologically concentrated or when a high dosage of drug is used. A report of Resistant (R) indicates that the antimicrobial is not likely to inhibit growth of the pathogen if the antimicrobial compound reaches the concentration usually achievable at the infection site; other therapy should be selected.
Quality ControlStandardized susceptibility test procedures require the use of laboratory controls to monitor and ensure the accuracy and precision of supplies and reagents used in the assay, and the techniques of the individuals performing the test.1,2 Standard metronidazole powder should provide a value within the MIC ranges noted in the following table:
|Quality control strain||Minimum Inhibitory Concentration (mcg/mL)|
|Bacteroides fragilis ATCC 25285||0.25 to 1.0||0.25 to 2.0|
|Bacteroides thetaiotaomicron ATCC 29741||0.5 to 2.0||0.5 to 4.0|
|Clostridium difficile ATCC 700057||0.125 to 0.5||–|
|Eggerthella lenta ATCC 43055||–||0.125 to 0.5|
For protozoal parasites:
Standardized tests do not exist for use in clinical microbiology laboratories.
Symptomatic Trichomoniasis. Metronidazole tablets are indicated for the treatment of T. vaginalis infection in females and males when the presence of the trichomonad has been confirmed by appropriate laboratory procedures (wet smears and/or cultures).
Asymptomatic Trichomoniasis. Metronidazole tablets are indicated in the treatment of asymptomatic T. vaginalis infection in females when the organism is associated with endocervicitis, cervicitis, or cervical erosion. Since there is evidence that presence of the trichomonad can interfere with accurate assessment of abnormal cytological smears, additional smears should be performed after eradication of the parasite.
Treatment of Asymptomatic Sexual Partners. T. vaginalis infection is a venereal disease. Therefore, asymptomatic sexual partners of treated patients should be treated simultaneously if the organism has been found to be present, in order to prevent reinfection of the partner. The decision as to whether to treat an asymptomatic male partner who has a negative culture or one for whom no culture has been attempted is an individual one. In making this decision, it should be noted that there is evidence that a woman may become reinfected if her sexual partner is not treated. Also, since there can be considerable difficulty in isolating the organism from the asymptomatic male carrier, negative smears and cultures cannot be relied upon in this regard. In any event, the sexual partner should be treated with metronidazole tablets in cases of reinfection.
Amebiasis. Metronidazole tablets are indicated in the treatment of acute intestinal amebiasis (amebic dysentery) and amebic liver abscess.
In amebic liver abscess, Metronidazole tablets therapy does not obviate the need for aspiration or drainage of pus.
Anaerobic Bacterial Infections. Metronidazole tablets are indicated in the treatment of serious infections caused by susceptible anaerobic bacteria. Indicated surgical procedures should be performed in conjunction with metronidazole tablets therapy. In a mixed aerobic and anaerobic infection, antimicrobials appropriate for the treatment of the aerobic infection should be used in addition to metronidazole tablets.
INTRA-ABDOMINAL INFECTIONS, including peritonitis, intra-abdominal abscess, and liver abscess, caused by Bacteroides species including the B. fragilis group (B. fragilis , B. distasonis , B. ovatus , B. thetaiotaomicron , B. vulgatus), Clostridium species, Eubacterium species, Peptococcus species , and Peptostreptococcus species.
SKIN AND SKIN STRUCTURE INFECTIONS caused by Bacteroides species including the B. fragilis group, Clostridium species, Peptococcus species , 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, Peptococcus species , Peptostreptococcus species, and Fusobacterium 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.
To reduce the development of drug-resistant bacteria and maintain the effectiveness of metronidazole and other antibacterial drugs, metronidazole should be used only to treat or prevent infections that are proven or strongly suspected to be caused by susceptible bacteria. When culture and susceptibility information are available, they should be considered in selecting or modifying antibacterial therapy. In the absence of such data, local epidemiology and susceptibility patterns may contribute to the empiric selection of therapy.
All MedLibrary.org resources are included in as near-original form as possible, meaning that the information from the original provider has been rendered here with only typographical or stylistic modifications and not with any substantive alterations of content, meaning or intent.