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Causality: well established
Causality assessment · Causality: well established
Natalizumab and Progressive multifocal leukoencephalopathy: 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.
Natalizumab ↔ Progressive multifocal leukoencephalopathy
n=2,127 co-reports · PRR 40.1 · ROR 40.6
Natalizumab carries a boxed warning for progressive multifocal leukoencephalopathy (PML), the best-known drug-associated JC-virus brain infection, with risk rising with longer exposure and prior immunosuppression; 2,127 co-reports give PRR 40.1. The label mandates risk stratification and monitoring.
Regulatory basis: natalizumab (Tysabri) prescribing information — boxed warning for PML; risk stratification and monitoring.
| Bradford Hill viewpoint | Status | Note |
|---|---|---|
| Temporality (necessary) | met | Months, risk rises with time |
| Strength | met | PRR 40.1, an extreme signal |
| Consistency | met | Reproduced across cohorts |
| Specificity | met | Fairly specific to natalizumab |
| Biological gradient | met | Duration/risk-factor related |
| Plausibility | met | Known JC-virus reactivation mechanism |
| Coherence | met | Fits natalizumab immunosuppression |
| Experiment | n/a | Too rare for trial detection |
| Analogy | met | Analogous to rituximab PML |
This table is this page's own qualitative read of the literature cited above, not an automated or citation-gated assessment — see the note at the bottom of this page.
✗ No ClinicalTrials.gov results-posting trial in the top search hits for natalizumab captured progressive multifocal leukoencephalopathy as a tracked adverse event in a usable structure. A rare opportunistic infection is not detectable in multiple-sclerosis trials.