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Weird and Wobbly – Maybe Metronidazole?

July 20, 2021

Written by Vivian Lei

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In a population of older adults, serious central and peripheral nervous system adverse events were associated with increased odds of metronidazole exposure relative to clindamycin.

Why does this matter?
Metronidazole is a common antibiotic that has anecdotally been reported to have an association with central and peripheral nervous system toxicity. This was the first large-scale study directed at investigating this association. Although the researchers found that overall toxicity is likely rare, the sheer number of prescriptions for metronidazole means a large number of patients may be at risk for serious complications.

Weird and wobbly? Maybe it was that antibiotic
In this population-based nested case-control study, researchers identified 1,212 adults ≥66 years of age in Ontario, Canada with new-onset encephalopathy, cerebellar dysfunction, or peripheral neuropathy within 100 days of a receiving a prescription for metronidazole or clindamycin. These cases were matched to 12,098 controls without any symptoms but who also received metronidazole or clindamycin within the preceding 100 days. Neurologic adverse events were significantly more likely to be associated with prior metronidazole exposure compared to clindamycin (OR 1.72, 95% CI 1.53–1.94). This association held after adjusting for demographics, healthcare utilization history, comorbidities, and other medications. In those receiving metronidazole, overall incidence of neurotoxicity at 100 days was 0.25%. CNS effects in this population were four times more common than peripheral neuropathy. The mechanism for metronidazole toxicity is not yet known, but prescribers and clinicians should be aware of these rare but potentially serious side effects.

Metronidazole-associated Neurologic Events: A Nested Case-control Study. Clin Infect Dis. 2021 Jun 15;72(12):2095-2100. doi: 10.1093/cid/ciaa395.

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