From the FDA Drug Label
Metronidazole has been shown to have in vitro and clinical activity against the following organisms: Anaerobic gram negative bacilli, including: Bacteroides species, including the Bacteroides fragilis group (B. fragilis, B. distasonis, B. ovatus, B. thetaiotaomicron, B vulgatus) Fusobacterium species A bacterial isolate may be considered susceptible if the MIC value for metronidazole is not more than 16 mcg/mL.
The treatment of Fusobacterium with metronidazole may be considered when the bacteria is detected, as it is active against this organism. However, the decision to treat should be based on clinical judgment, considering the low microbial load and other factors such as symptoms and patient health. 1
From the Research
Treatment of fusobacterium infection detected at low microbial load on pharyngeal PCR is generally not recommended without clinical symptoms. Asymptomatic colonization of fusobacterium in the pharynx is common and often represents normal flora rather than pathogenic infection. If the patient has no symptoms such as sore throat, fever, or difficulty swallowing, watchful waiting is appropriate. However, if clinical symptoms are present alongside the PCR finding, treatment with amoxicillin-clavulanate (875/125 mg twice daily for 7-10 days) or, in penicillin-allergic patients, clindamycin (300-450 mg four times daily for 7-10 days) would be appropriate, as suggested by the most recent study 2. Metronidazole (500 mg three times daily for 7-10 days) is another alternative that targets anaerobes effectively. The decision to treat should be based on clinical presentation rather than PCR results alone, as unnecessary antibiotic use can lead to resistance and disruption of normal microbiota.
Some key points to consider:
- Fusobacterium species are anaerobic bacteria that normally inhabit the oral cavity and upper respiratory tract, and only become pathogenic when they invade tissues or when the host's immune system is compromised 3.
- The prevalence of F. necrophorum was similar to that of Streptococcus pyogenes in patients with pharyngitis in Japan, suggesting that F. necrophorum is an important causative agent of bacterial pharyngitis 4.
- A study from a Japanese university hospital found that all Fusobacterium isolates were sensitive to β-lactam/β-lactamase inhibitors, carbapenems, and metronidazole, which can guide empirical treatments 2.
- Another study found that delayed start of appropriate antimicrobial therapy did not impact the outcomes of patients with Fusobacterium bacteremia, but shock, lack of fever at presentation, and underlying diseases were independent risk factors for mortality 5.
Overall, the management of fusobacterium infection should prioritize the patient's clinical presentation and symptoms, rather than relying solely on PCR results, to minimize unnecessary antibiotic use and potential harm.