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Causality: well established
Causality assessment · Causality: well established
Ondansetron (5-HT3 antagonists) and QT prolongation / torsades: 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.
Ondansetron (5-HT3 antagonists) ↔ QT prolongation / torsades
n=1,167 co-reports · PRR 6.4 · ROR 6.5
Ondansetron, a widely used anti-nausea drug, can prolong the cardiac QT interval and has been linked to rare torsades de pointes, particularly with intravenous doses or in patients with electrolyte disturbance or other QT-prolonging drugs. This led regulators to lower the maximum single intravenous dose. The effect is genuine and dose-related rather than idiosyncratic, and it is the reason ECG caution is advised in at-risk patients. The 1,167 co-reports (PRR 6.4) reflect ondansetron's very wide use in surgery, cancer care, and pregnancy.
Regulatory basis: ondansetron prescribing information and FDA dose-limit change (2012) over QT prolongation.
| Bradford Hill viewpoint | Status | Note |
|---|---|---|
| Temporality (necessary) | met | QT prolongation is measured during treatment and resolves after the drug is cleared |
| Strength | met | PRR 6 on a large co-report count |
| Consistency | met | Reproduced across ECG studies and case series |
| Specificity | partial | A class effect of 5-HT3 antagonists, strongest for some agents |
| Biological gradient | partial | Dose-related, especially with intravenous use |
| Plausibility | met | hERG-channel blockade delays cardiac repolarisation |
| Coherence | met | Coheres with the regulatory dose-limit change and ECG cautions |
| Experiment | partial | Support from ECG studies; no randomized arrhythmia RCT |
| Analogy | met | Analogous to QT risk with other 5-HT3 antagonists and QT-prolonging drugs |
This page's own qualitative read, not an automated/citation-gated assessment.
✗ No ClinicalTrials.gov results-posting trial in the top search hits for ondansetron captured QT prolongation or torsades; the risk was characterised through ECG studies and the dose-limit regulatory action rather than a trial AE table.