The antibiotic must also have a bactericidal effect on the pathogen.
There have been advances in microbial definition of bacterial brain abscess. The identification of Bacteroides fragilis as a pathogen in certain brain abscesses has established a role for a newly available antibiotic, metronidazole. The study of the pathological distinction between cerebritis and frank abscess is clarifying two clinical characteristics of brain abscess: the limited success of antibiotic treatment and the increase in intracranial pressure 1).
The clinical effectiveness of tertiary-generation cephalosporin+vancomycin+metronidazole for bacterial brain abscess was 88%. Therefore, combined antibiotics in cases with no evidence of positive culture in brain abscess are strongly recommended 2).
IV antibiotics for 6-8 weeks (most commonly 6) may then D/C even if the CT abnormalities persist (neovascularity remains). NB: CT improvement may lag behind clinical improvement.Duration of treatment may be reduced if abscess and capsule entirely excised surgically. Oral antibiotics may be used following IV course.
Antimicrobial treatment for a brain abscess is generally long (6-8 wk) because of the prolonged time needed for brain tissue to repair and close abscess space. The United Kingdom treatment guidelines advocate 4-6 weeks if the abscess has been drained or removed and 6-8 weeks if drainage occurred 3).
The duration of therapy can be adjusted according to the patient’s condition, causative organism(s), number of abscesses and their size, and response to treatment. A shorter course (4-6 wk) may suffice for cerebritis and in patients who underwent surgical drainage 4).
A long course (>6 wk) is required for necrotic and/or encapsulated abscess with tissue necrosis, multiloculated abscess, abscesses in vital intracranial locations (ie, brain steam), and in immunocompromise.
The length of therapy is guided by continuous assessment of the clinical course and followup imaging studies. The antimicrobial therapy is continued until a clinical response occurs and CT or MRI findings show resolution. However, because the abscess site may show persistent enhancement for several months. This finding alone is not an indication to continue antimicrobial therapy or for surgical drainage 5).