Metronidazole Neurotoxicity in a Dog

The dog in the video below was treated for gastro-intestinal disease with metronidazole orally at 17 mg/kg BID. He developed rapidly progressive cerebellar-quality generalized ataxia and a mild, intermittent head tilt as well as positional nystagmus.

The MR study shown above revealed bilaterally symmetrical well-defined intra-axial lesions at the level of the dentate cerebellar nuclei. These lesions are homogeneous, T2W and FLAIR moderately hyperintense to gray matter, T1W isointense, and not associated with contrast enhancement or signal void. There is no perilesional edema or mass effect. These lesions are hyperintense on DWI and restrictive on ADC.

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In view of the history and MR findings, metronidazole neurotoxicosis was suspected and metronidazole was immediately discontinued. Oral diazepam was prescribed for one week; this treatment has been reported to hasten the recovery response time in such cases. The dog spontaneously improved over a few days.

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Metronidazole is commonly used to treat bacterial and protozoal infections in small animals. Its use can however sometimes cause neurotoxicity. The exact mechanism is unknown with the proposed mechanisms including inhibition of neuronal protein synthesis by binding to RNA and thiamine antagonism. The toxic dose is generally stated as >60 mg/kg/day; however, lower dosages have been reported to cause neurotoxicity even after a few days of administration suggesting a possible idiosyncratic effect.

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We a very grateful to the owner of this dog for allowing us to use this video for teaching purposes.

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Courtesy of Jonathan Bell and Laura Keyser at Swift Referrals, England