metronidazole , a nitroimidazole antimicrobial agent is widely used in the treatment of anerobic and protozoal infections for more than three decades .
common side effects are nausea , vomiting , abdominal discomfort , headache , and metallic taste .
neurological effects such as ataxia , dizziness , peripheral neuropathy , and seizures were also reported .
we report a rare case of metronidazole - induced encephalopathy ( mie ) in order to create an awareness of this unusual entity among practitioners . a 39-year - old male without any comorbidities
was brought to the emergency department for acute onset of slurring of speech , generalized weakness , and unsteadiness .
he was unable to button his shirt , and turn a doorknob due to clumsiness of hands and fingers for the past 24 hours .
four days prior to this admission , he complained of numbness and tingling sensation of toes and dorsum of both feet .
recently , he was treated for amebic liver abscess with ultrasound - guided aspiration and was given tablet metronidazole 800 mg three times a day for 2 weeks . since repeat ultrasound revealed re - accumulation of liver abscess after 2 weeks
, he was advised to continue metronidazole 800 mg three times a day orally for 2 more weeks .
thus , he had taken 67.2 grams of tablet metronidazole over a period of 28 days .
neurologic examination revealed the patient was conscious but confused , with dysarthria , nystagmus , dysmetria on finger - to - nose test , positive romberg 's sign ; graded sensory loss to pain , temperature , touch , and proprioception over distal lower and upper extremities in a stocking and glove type , and impaired joint position and vibration sense .
clinical assessment of cranial nerve , muscular system , deep tendon reflexes , and gait was normal with absent babinski sign .
his hematological , metabolic panel , thyroid profile , cerebrospinal fluid ( csf ) analysis , viral markers , arterial blood gas , ammonia levels , vitamin b1 , b12 , and folate levels were within normal limits but for mild derangement of liver function .
his magnetic resonance imaging ( mri ) brain revealed symmetrical areas of altered signal intensity , appearing hyperintense on t2w and fluid - attenuated inversion recovery ( flair ) images , and involving the dentate nuclei and splenium of the corpus callosum .
there was an evidence of diffusion restriction on diffusion - weighted / apparent diffusion coefficient mapping without evidences of hemorrhage or infarct .
imaging findings were in favor of metronidazole toxicity , which was supported by the prolonged history of metronidazole intake .
moreover , his symptoms disappeared on third day after discontinuation of metronidazole , and mri 4 months later showed resolution of the earlier described signal changes .
mie usually occurs at doses exceeding a total of 50 grams / month or 1.5 to 2 grams / day .
although the exact mechanisms are unknown , the possible mechanisms with experimental evidences are furnished .
furthermore , cerebellum of rats has been shown to uptake carbon labeled metronidazole . in vitro ,
metronidazole incorporated into thiamine analogs , inhibits the phosphorylation of thiamine , thereby antagonizing vitamin b1 effect .
radiolabelled metronidazole binds ribonucleic acid ( rna ) in a significant manner , and inhibits neuronal protein synthesis and facilitates degeneration .
catecholamine neurotransmitters are oxidized by metronidazole derivatives to produce semiquinone and nito anion radicals which are neurotoxic .
the case is presented so as to facilitate practitioners to recognize the symptoms and signs of metronidazole toxicity , and consider them in their differential diagnosis .
it is worth to remember the potential neurological abnormalities and imaging findings of this entity , as this agent is frequently prescribed and used in clinical practice .
 encephalopathy associated with metronidazole administration is an uncommon but potentially reversible disease and depends on the cumulative metronidazole dose , and most patients with this condition recover rapidly after discontinuation of therapy . 
 we present a case as well as a review of the literature regarding this rare but serious adverse event . 