[Clinical Characteristics of Metronidazole-induced Encephalopathy: A Report of Two Cases and a Review of 32 Japanese Cases in the Literature].

Metronidazole is an antibiotic classically used against most anaerobic bacteria and protozoa. Because an intravenous form of metronidazole has recently entered the market, the use of this antibiotic is attracting renewed interest in many clinical settings in Japan. However, neurotoxicity is a major adverse event: in the central nervous system metronidazole-induced encephalopathy is a rare but serious condition. We performed a literature review of 34 cases including 2 of our cases, 25 from domestic conference abstracts, and 7 cases presented in full research papers. The mean patient age was 64.7 years. The conditions most commonly treated with metronidazole were brain abscess (35.3%), liver abscess (17.6%), and Clostridium difficile infection (14.7%). The most common predisposing conditions were liver dysfunction (26.5%), diabetes and other metabolic disorders (20.6%), and hematologic or solid organ malignancy (14.7%). The mean period of administration before the onset of encephalopathy symptoms was 61.3 days, and the mean total dose was 95.9g. The initial chief complaints were dysarthria (in 70.6% of the cases) and ataxia (61.8%); 82.4% of the cases were diagnosed on the basis of MRI (T2-weighted or FLAIR imaging). The key imaging finding was high intensity in the dentate nucleus bilaterally (82.4%). Stopping the metronidazole led to symptom remission within 8.5 days, but the MRI changes remained longer than the clinical symptoms. Two patients (6.0%) developed irreversible disturbance of consciousness. Although the mechanisms of this type of encephalopathy have not yet been elucidated, localized nerve-cell edema is likely caused by decreased metronidazole metabolism associated with liver and metabolic dysfunction. Careful observation for neurologic signs should be conducted during the treatment of brain abscesses associated with metronidazole administration, because patients with brain abscesses are naturally at high risk of metronidazole-induced encephalopathy.