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Causality: well established
Causality assessment · Causality: well established
Metronidazole and Peripheral neuropathy: is the FAERS signal real?
A written Bradford Hill assessment of one drug–event pair. The grade is a judgement about the signal, not a statement that this drug causes this event in any one person; FAERS counts are reports, not rates.
Metronidazole ↔ Peripheral neuropathy
n=899 co-reports · PRR 3.2 · ROR 3.2
Metronidazole can cause a dose- and duration-dependent peripheral neuropathy, typically a painful sensory disturbance of the feet that becomes more likely with prolonged courses or high cumulative doses. It is a genuine drug effect, resolves slowly after withdrawal in many patients, and is the reason long-term metronidazole therapy is closely watched. The 899 co-reports (PRR 3.2) reflect both the real association and metronidazole's very wide use across infection, dental, and gut indications.
Regulatory basis: metronidazole prescribing information (peripheral neuropathy warning, especially with prolonged therapy). Established metronidazole-neuropathy literature.
| Bradford Hill viewpoint | Status | Note |
|---|---|---|
| Temporality (necessary) | met | Neuropathy emerges during prolonged therapy and often improves slowly after withdrawal |
| Strength | partial | PRR 3 with a large co-report count — a modest but broad signal |
| Consistency | met | Reproduced across decades of metronidazole case series |
| Specificity | met | A recognised drug cause of peripheral neuropathy |
| Biological gradient | met | Cumulative-dose- and duration-related |
| Plausibility | met | Likely axonal injury from the drug's neurotoxic metabolites |
| Coherence | met | Coheres with the labelled warning and the practice of limiting long courses |
| Experiment | partial | Dechallenge (withdrawal) usually improves symptoms, though recovery can be slow; no randomized trial |
| Analogy | met | Analogous to neuropathy from other drugs (isoniazid, nitrofurantoin, chemotherapy) |
This page's own qualitative read, not an automated/citation-gated assessment.
✗ No ClinicalTrials.gov results-posting trial in the top search hits for metronidazole captured peripheral neuropathy; the effect requires prolonged exposure and is identified in clinical practice rather than a trial AE table.