Causality assessment · Causality: well established

Fondaparinux and Thrombocytopenia: is the FAERS signal real?

n=263 co-reports · PRR 6.2 · ROR 6.3

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.

Causality: well established

Fondaparinux ↔ Thrombocytopenia

n=263 co-reports · PRR 6.2 · ROR 6.3

Fondaparinux is a synthetic indirect factor-Xa inhibitor; thrombocytopenia is a recognised, if less common, effect (263 co-reports, PRR 6.2) and, in a minority, is associated with the same platelet-activating antibodies that cause heparin-induced thrombocytopenia. The label advises platelet counts at baseline and periodically, and the drug is contraindicated in active bleeding or severe renal impairment.

Regulatory basis: fondaparinux (Arixtra) prescribing information — thrombocytopenia; platelet monitoring.

Bradford Hill viewpoint	Status	Note
Temporality (necessary)	met	Platelet fall within days
Strength	met	PRR 6.2, moderate
Consistency	met	Recognised in case series
Specificity	partial	Shared with heparins
Biological gradient	not established	Not clearly dose-related
Plausibility	met	Immune-mediated platelet activation proposed
Coherence	met	Fits the anticoagulant picture
Experiment	n/a	Not tested as a trial endpoint
Analogy	met	Analogous to heparin-induced thrombocytopenia

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.

✓ Trial evidence found — EINSTEIN Junior: Oral Rivaroxaban in Children With Venous Thrombosis (NCT02234843)

Adverse event	Comparator Group (n=162) · Rivaroxaban Group (n=329)
Thrombocytopenia	0/162	2/329

Post-marketing signal terms appear in this trial's posted adverse-event tables; per-arm counts shown as affected/at-risk. View on ClinicalTrials.gov →