WARNING Metronidazole has been shown to be carcinogenic in mice and rats (see PRECAUTIONS). Unnecessary use of the drug should be avoided. Its use should be reserved for the conditions described in the INDICATIONS AND USAGE section below.
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Central and Peripheral Nervous System Effects Encephalopathy and peripheral neuropathy: Cases of encephalopathy and peripheral neuropathy (including optic neuropathy) have been reported with metronidazole. Encephalopathy has been reported in association with cerebellar toxicity characterized by ataxia, dizziness, and dysarthria. CNS lesions seen on MRI have been described in reports of encephalopathy. CNS symptoms are generally reversible within days to weeks upon discontinuation of metronidazole. CNS lesions seen on MRI have also been described as reversible. Peripheral neuropathy, mainly of sensory type has been reported and is characterized by numbness or paresthesia of an extremity. Convulsive seizures have been reported in patients treated with metronidazole. Aseptic meningitis: Cases of aseptic meningitis have been reported with metronidazole. Symptoms can occur within hours of dose administration and generally resolve after metronidazole therapy is discontinued. The appearance of abnormal neurologic signs and symptoms demands the prompt evaluation of the benefit/risk ratio of the continuation of therapy (see ADVERSE REACTIONS). Risk of Hepatotoxicity and Death in Patients with Cockayne Syndrome Cases of severe hepatotoxicity/acute hepatic failure, including cases with a fatal outcome with very rapid onset after treatment initiation in patients with Cockayne syndrome have been reported with products containing metronidazole for systemic use. In this population, metronidazole should therefore be used after careful benefit-risk assessment and only if no alternative treatment is available. Obtain liver function tests prior to the start of therapy, within the first 2-3 days after initiation of therapy, frequently during therapy and after end of treatment. Discontinue metronidazole if elevation of liver function tests occurs, and monitor liver function tests until the baseline values are reached. Advise patients with Cockayne syndrome to stop taking metronidazole immediately if they experience any symptoms of potential liver injury, such as abdominal pain, nausea, change in stool color or jaundice, and to contact their healthcare provider.