Fondaparinux side effects: what 8,045 FDA adverse event reports show
Drug class
Factor xa inhibitor (anticoagulant)
Label matched
Fondaparinux Sodium (Fondaparinux Sodium)
Who reports
8,045 reports · 88% serious · 1,438 with death outcome · 57% female
Used for
Fondaparinux sodium injection is a Factor Xa inhibitor (anticoagulant) indicated for: • Prophylaxis of deep vein thrombosis (DVT) in adult patients undergoing hip fracture surgery (including extended prophylaxis), hip replacement surgery, knee replacement surgery, or abdominal surgery. ( 1.1 ) • Treatment of DVT or acute pulmonary embolism (PE) in adult patients when administered in conjunction with warfarin sodium.
What it is
Fondaparinux sodium injection, USP is a sterile solution containing fondaparinux sodium. It is a synthetic and specific inhibitor of activated Factor X (Xa). Fondaparinux sodium is methyl O -2.
Boxed warning
SPINAL/EPIDURAL HEMATOMAS Epidural or spinal hematomas may occur in patients who are anticoagulated with low molecular weight heparins (LMWH), heparinoids, or fondaparinux sodium and are receiving neuraxial anesthesia or undergoing spinal puncture. These hematomas may result in long-term or permanent paralysis.
Causality screen of the 40 strongest signals
What the badges mean
- Labeled — boxed warning The term (or its clinical synonym) appears in the FDA boxed warning: causality is regulator-recognised and considered serious.
- Labeled adverse reaction The exact term appears in the label's warnings or adverse-reactions sections: a known, expected effect. The FAERS signal confirms the label rather than discovering anything.
- Labeled (related wording) The label describes this effect under different wording (e.g. 'neutropenia' for 'neutrophil count decreased'). Treated as known.
- Reporting / coding artifact An administrative, monitoring or exposure term (product issue, off-label use, 'test normal', overdose...). Not a biological reaction; a high PRR here reflects how reports are coded.
- Lab value / disease marker A laboratory result, investigation or disease-activity marker (antibody positive, CRP abnormal, swollen joint count) not described in the label. These usually mirror the monitored disease or testing protocol rather than a drug effect; not screened further.
- Not in label — unassessed Not found in the label text, not an artifact pattern. This is a genuine candidate for a formal causality assessment (Bradford Hill / WHO-UMC); it has NOT had one here.
Strongest disproportionality signals
Flagged terms (PRR ≥ 2, χ² ≥ 4, n ≥ 10), ranked by PRR; infinite PRRs (no comparator reports) excluded. The EBGM column is a second, shrinkage-based estimate (MGPS) with its 5th percentile EB05 and the BCPNN IC025; a pair flagged by PRR alone is marked PRR-only and should be read as fragile. The strata column recomputes the PRR on serious reports only and flags pairs whose reports are unusually skewed by sex or come mostly from consumers rather than clinicians. 982 further terms are in the interactive explorer. Reaction links open the term's cross-drug page.
| Reaction | Reports | PRR 95% CI · ROR · χ²/p | EBGM EB05 · IC025 | Label screen | Serious-only & strata | Trial cross-check |
|---|---|---|---|---|---|---|
| Ureteric compression | 12 | 489.7 264.2–907.5ROR 490.4 · χ² 4,514 / p <1e-300 | 248.8 EB05 151.7 · IC025 +3.6 3/3 methods agree | Not in label — unassessed | serious n=12 | no trial data cached |
| Sinobronchitis | 17 | 331.1 199.9–548.4ROR 331.8 · χ² 4,668 / p <1e-300 | 220.9 EB05 146.0 · IC025 +4.2 3/3 methods agree | Not in label — unassessed | serious n=17 | no trial data cached |
| Incision site haematoma | 25 | 315.0 208.1–477.0ROR 316.0 · χ² 6,695 / p <1e-300 | 231.3 EB05 164.7 · IC025 +4.8 3/3 methods agree | Not in label — unassessed | serious n=25 | no trial data cached |
| Hypersensitivity myocarditis | 11 | 259.4 139.6–482.1ROR 259.8 · χ² 2,343 / p <1e-300 | 167.7 EB05 99.9 · IC025 +3.4 3/3 methods agree | Not in label — unassessed | serious n=11 | no trial data cached |
| Muscle haemorrhage | 215 | 147.8 129.0–169.3ROR 151.8 · χ² 29,509 / p <1e-300 | 138.1 EB05 123.3 · IC025 +6.5 3/3 methods agree | Not in label — unassessed | serious n=215 | no trial data cached |
| Intra-abdominal haematoma | 64 | 141.5 110.1–181.8ROR 142.6 · χ² 8,329 / p <1e-300 | 129.1 EB05 104.6 · IC025 +5.6 3/3 methods agree | Not in label — unassessed | serious n=63 | no trial data cached |
| Breast haematoma | 10 | 118.5 62.9–223.2ROR 118.6 · χ² 1,004 / p 1e-220 | 93.6 EB05 54.3 · IC025 +3.1 3/3 methods agree | Not in label — unassessed | serious n=9 | no trial data cached |
| Incision site haemorrhage | 34 | 113.4 80.5–159.7ROR 113.8 · χ² 3,520 / p <1e-300 | 102.5 EB05 76.7 · IC025 +4.8 3/3 methods agree | Not in label — unassessed | serious n=34 | no trial data cached |
| Thrombocythaemia | 20 | 96.6 61.9–151.0ROR 96.9 · χ² 1,734 / p <1e-300 | 85.8 EB05 58.6 · IC025 +4.1 3/3 methods agree | Not in label — unassessed | serious n=20 | no trial data cached |
| Gastroduodenal ulcer | 15 | 96.6 57.7–161.8ROR 96.8 · χ² 1,278 / p 4e-280 | 83.6 EB05 53.8 · IC025 +3.7 3/3 methods agree | Not in label — unassessed | serious n=15 | no trial data cached |
| Post procedural haematoma | 59 | 93.9 72.5–121.6ROR 94.5 · χ² 5,141 / p <1e-300 | 88.1 EB05 70.8 · IC025 +5.3 3/3 methods agree | Reporting / coding artifact | serious n=58 · 95% clinician | no trial data cached |
| Retroperitoneal haematoma | 74 | 90.8 72.1–114.4ROR 91.7 · χ² 6,265 / p <1e-300 | 85.9 EB05 70.7 · IC025 +5.4 3/3 methods agree | Labeled (related wording) related wording | serious n=74 | no trial data cached |
| Abdominal wall haematoma | 60 | 82.9 64.2–107.1ROR 83.5 · χ² 4,624 / p <1e-300 | 78.4 EB05 63.1 · IC025 +5.2 3/3 methods agree | Labeled (related wording) related wording | serious n=59 | no trial data cached |
| Spontaneous haematoma | 21 | 75.7 49.1–116.8ROR 75.9 · χ² 1,432 / p <1e-300 | 69.1 EB05 47.7 · IC025 +4.0 3/3 methods agree | Not in label — unassessed | serious n=21 | no trial data cached |
| Prothrombin level decreased | 26 | 73.1 49.6–107.9ROR 73.4 · χ² 1,729 / p <1e-300 | 67.7 EB05 48.6 · IC025 +4.3 3/3 methods agree | Lab value / disease marker | serious n=26 | no trial data cached |
| Spinal cord haemorrhage | 11 | 72.9 40.0–132.7ROR 73.0 · χ² 690 / p 2e-152 | 63.5 EB05 37.8 · IC025 +3.1 3/3 methods agree | Labeled (related wording) related wording | serious n=11 | no trial data cached |
| Adrenal haemorrhage | 15 | 71.1 42.6–118.8ROR 71.3 · χ² 942 / p 3e-207 | 63.9 EB05 41.1 · IC025 +3.6 3/3 methods agree | Labeled (related wording) related wording | serious n=15 | no trial data cached |
| Operative haemorrhage | 12 | 71.1 40.1–126.1ROR 71.2 · χ² 740 / p 3e-163 | 62.6 EB05 38.2 · IC025 +3.2 3/3 methods agree | Labeled adverse reaction exact term | serious n=12 | no trial data cached |
| Traumatic haematoma | 27 | 66.9 45.7–97.9ROR 67.1 · χ² 1,644 / p <1e-300 | 62.5 EB05 45.1 · IC025 +4.3 3/3 methods agree | Labeled (related wording) related wording | serious n=27 | no trial data cached |
| Heparin-induced thrombocytopenia | 122 | 65.9 55.1–78.7ROR 66.9 · χ² 7,537 / p <1e-300 | 63.6 EB05 54.7 · IC025 +5.4 3/3 methods agree | Labeled adverse reaction exact term | serious n=120 | no trial data cached |
| Haematoma infection | 14 | 65.2 38.4–110.8ROR 65.3 · χ² 802 / p 1e-176 | 58.8 EB05 37.2 · IC025 +3.4 3/3 methods agree | Labeled (related wording) related wording | serious n=14 | no trial data cached |
| Subcutaneous haematoma | 30 | 62.4 43.5–89.6ROR 62.6 · χ² 1,710 / p <1e-300 | 58.8 EB05 43.2 · IC025 +4.3 3/3 methods agree | Labeled (related wording) related wording | serious n=30 · ♀ 77% (drug 57%) | no trial data cached |
| Intracranial haematoma | 13 | 61.4 35.5–106.4ROR 61.5 · χ² 697 / p 7e-154 | 55.4 EB05 34.5 · IC025 +3.3 3/3 methods agree | Labeled (related wording) related wording | serious n=13 | no trial data cached |
| Haematoma | 559 | 57.2 52.8–62.0ROR 61.4 · χ² 30,191 / p <1e-300 | 55.9 EB05 52.1 · IC025 +5.6 3/3 methods agree | Labeled — boxed warning exact term | serious PRR 37.8 | no trial data cached |
| Shock haemorrhagic | 174 | 57.0 49.1–66.1ROR 58.2 · χ² 9,315 / p <1e-300 | 55.5 EB05 48.9 · IC025 +5.3 3/3 methods agree | Not in label — unassessed | serious PRR 36.4 | no trial data cached |
| Peritoneal haemorrhage | 29 | 54.9 38.0–79.2ROR 55.1 · χ² 1,449 / p <1e-300 | 52.0 EB05 38.0 · IC025 +4.2 3/3 methods agree | Labeled (related wording) related wording | serious n=29 | no trial data cached |
| Haematoma muscle | 24 | 54.2 36.2–81.2ROR 54.4 · χ² 1,176 / p 4e-258 | 51.1 EB05 36.1 · IC025 +4.0 3/3 methods agree | Not in label — unassessed | serious n=24 · ♀ 26% (drug 57%) · 92% clinician | no trial data cached |
| Allergic sinusitis | 17 | 52.5 32.5–84.9ROR 52.6 · χ² 792 / p 1e-174 | 48.9 EB05 32.3 · IC025 +3.6 3/3 methods agree | Not in label — unassessed | serious n=17 | no trial data cached |
| Extradural haematoma | 26 | 52.0 35.3–76.6ROR 52.1 · χ² 1,225 / p 1e-268 | 49.2 EB05 35.3 · IC025 +4.1 3/3 methods agree | Not in label — unassessed | serious n=26 | no trial data cached |
| Urine colour abnormal | 10 | 46.1 24.7–86.1ROR 46.1 · χ² 390 / p 4e-87 | 41.9 EB05 24.3 · IC025 +2.8 3/3 methods agree | Lab value / disease marker | serious n=10 | no trial data cached |
| Pulpitis dental | 15 | 42.9 25.8–71.5ROR 43.0 · χ² 564 / p 6e-125 | 40.3 EB05 25.9 · IC025 +3.3 3/3 methods agree | Not in label — unassessed | serious n=15 | no trial data cached |
| Retroperitoneal haemorrhage | 39 | 41.8 30.5–57.3ROR 42.0 · χ² 1,488 / p <1e-300 | 40.4 EB05 30.8 · IC025 +4.2 3/3 methods agree | Labeled (related wording) related wording | serious n=39 | no trial data cached |
| Cerebral haematoma | 51 | 40.2 30.5–53.0ROR 40.5 · χ² 1,882 / p <1e-300 | 39.1 EB05 30.9 · IC025 +4.4 3/3 methods agree | Not in label — unassessed | serious n=52 | no trial data cached |
| Intra-abdominal haemorrhage | 36 | 39.8 28.7–55.3ROR 40.0 · χ² 1,305 / p 6e-286 | 38.5 EB05 29.1 · IC025 +4.1 3/3 methods agree | Not in label — unassessed | serious n=36 | no trial data cached |
| Pyelocaliectasis | 14 | 39.8 23.5–67.4ROR 39.8 · χ² 484 / p 2e-107 | 37.4 EB05 23.6 · IC025 +3.2 3/3 methods agree | Not in label — unassessed | serious n=14 | no trial data cached |
| Investigation | 46 | 38.3 28.6–51.2ROR 38.5 · χ² 1,609 / p <1e-300 | 37.2 EB05 29.0 · IC025 +4.3 3/3 methods agree | Lab value / disease marker | serious n=46 · 89% consumer | no trial data cached |
| Haemorrhagic anaemia | 63 | 37.3 29.1–47.8ROR 37.6 · χ² 2,161 / p <1e-300 | 36.4 EB05 29.5 · IC025 +4.4 3/3 methods agree | Labeled (related wording) related wording | serious n=63 | no trial data cached |
| Tooth erosion | 16 | 37.1 22.7–60.7ROR 37.2 · χ² 519 / p 4e-115 | 35.2 EB05 23.0 · IC025 +3.3 3/3 methods agree | Not in label — unassessed | serious n=16 | no trial data cached |
| Pupils unequal | 15 | 34.1 20.5–56.8ROR 34.2 · χ² 444 / p 8e-99 | 32.4 EB05 20.9 · IC025 +3.2 3/3 methods agree | Not in label — unassessed | serious n=15 | no trial data cached |
| Arterial haemorrhage | 14 | 32.1 19.0–54.4ROR 32.2 · χ² 387 / p 2e-86 | 30.6 EB05 19.3 · IC025 +3.0 3/3 methods agree | Labeled (related wording) related wording | serious n=14 | no trial data cached |
Trial evidence (ClinicalTrials.gov)
Most frequently reported reactions
By raw co-report count, regardless of disproportionality. Common terms here are often the illness itself or generic outcomes.
| Reaction | Reports | PRR 95% CI · ROR · χ²/p | EBGM EB05 · IC025 | Label screen | Serious-only & strata | Trial cross-check |
|---|---|---|---|---|---|---|
| Anaemia (low red blood cells) | 610 | 8.4 7.7–9.0ROR 9.0 · χ² 3,965 / p <1e-300 | 8.3 EB05 7.8 · IC025 +2.9 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 6.0 | no trial data cached |
| Haematoma | 559 | 57.2 52.8–62.0ROR 61.4 · χ² 30,191 / p <1e-300 | 55.9 EB05 52.1 · IC025 +5.6 3/3 methods agree | Labeled — boxed warning exact term | serious PRR 37.8 | no trial data cached |
| Pulmonary embolism (lung blood clot) | 448 | 12.3 11.2–13.4ROR 12.9 · χ² 4,631 / p <1e-300 | 12.2 EB05 11.3 · IC025 +3.4 3/3 methods agree | Likely indication confounding term in indications; also in warnings | serious PRR 8.0 | no trial data cached |
| Off label use (used outside approved label) | 371 | 1.1 1.0–1.2ROR 1.1 · χ² 4 / p 0.018 | 1.1 EB05 1.0 · IC025 -0.0 PRR-only: not supported by EBGM or IC | Reporting / coding artifact | serious PRR 1.3 | no trial data cached |
| Haemorrhage | 351 | 8.8 7.9–9.7ROR 9.1 · χ² 2,414 / p <1e-300 | 8.7 EB05 7.9 · IC025 +2.9 3/3 methods agree | Labeled — boxed warning exact term | serious PRR 6.9 | no trial data cached |
| Haemoglobin decreased | 339 | 8.6 7.8–9.6ROR 8.9 · χ² 2,276 / p <1e-300 | 8.5 EB05 7.8 · IC025 +2.9 3/3 methods agree | Labeled (related wording) related wording | serious PRR 6.0 | no trial data cached |
| Death | 297 | 0.9 0.8–1.0ROR 0.9 · χ² 3 / p 0.032 | 0.9 EB05 0.8 · IC025 -0.3 PRR-only: not supported by EBGM or IC | Outcome field, not a reaction | serious PRR 0.6 | no trial data cached |
| Deep vein thrombosis (leg blood clot) | 294 | 11.8 10.5–13.2ROR 12.2 · χ² 2,885 / p <1e-300 | 11.7 EB05 10.6 · IC025 +3.3 3/3 methods agree | Likely indication confounding term in indications; also in warnings | serious PRR 7.7 | no trial data cached |
| Dyspnoea (shortness of breath) | 271 | 1.2 1.1–1.4ROR 1.3 · χ² 14 / p 1e-4 | 1.2 EB05 1.1 · IC025 +0.1 | Not in label — unassessed | serious PRR 1.1 | no trial data cached |
| Thrombocytopenia (low platelets) | 263 | 6.2 5.5–6.9ROR 6.3 · χ² 1,135 / p 5e-249 | 6.1 EB05 5.5 · IC025 +2.4 3/3 methods agree | Labeled — boxed warning exact term | serious PRR 4.1 | no trial data cached |
| Drug ineffective (drug did not work) | 260 | 0.5 0.5–0.6ROR 0.5 · χ² 127 / p 1e-29 | 0.5 EB05 0.5 · IC025 -1.2 PRR-only: not supported by EBGM or IC | Reporting / coding artifact | serious PRR 0.9 | no trial data cached |
| Pyrexia (fever) | 240 | 1.8 1.6–2.0ROR 1.8 · χ² 87 / p 5e-21 | 1.8 EB05 1.6 · IC025 +0.6 | Not in label — unassessed | serious PRR 1.3 | no trial data cached |
| Nausea | 234 | 0.8 0.7–0.9ROR 0.8 · χ² 16 / p 3e-5 | 0.8 EB05 0.7 · IC025 -0.6 PRR-only: not supported by EBGM or IC | Not in label — unassessed | serious PRR 0.8 | no trial data cached |
| Thrombosis | 233 | 7.5 6.6–8.6ROR 7.7 · χ² 1,318 / p 9e-289 | 7.4 EB05 6.7 · IC025 +2.7 3/3 methods agree | Likely indication confounding term in indications; also in warnings | serious PRR 4.8 | no trial data cached |
| Vomiting | 231 | 1.3 1.1–1.5ROR 1.3 · χ² 15 / p 7e-5 | 1.3 EB05 1.2 · IC025 +0.1 | Not in label — unassessed | serious PRR 1.2 | no trial data cached |
Unlabeled candidate signals
These flagged terms were not found in the FDA label text and do not match an artifact pattern. They are the pairs that would merit a structured assessment (temporality, dose-response, biological plausibility, consistency across databases, trial or cohort evidence). The screen has not done that; string-matching misses label wording, and a strong PRR can still be stimulated reporting, co-medication, or the disease itself.
- Incision site haematoma — n=25, PRR 315.0
- Muscle haemorrhage — n=215, PRR 147.8
- Intra-abdominal haematoma — n=64, PRR 141.5
- Incision site haemorrhage — n=34, PRR 113.4
- Thrombocythaemia — n=20, PRR 96.6
- Spontaneous haematoma — n=21, PRR 75.7
- Shock haemorrhagic — n=174, PRR 57.0
- Haematoma muscle — n=24, PRR 54.2
- Extradural haematoma — n=26, PRR 52.0
- Cerebral haematoma — n=51, PRR 40.2
✓ A hand-written Bradford Hill causality assessment exists for this drug: Fondaparinux ↔ Thrombocytopenia.
Want to assess one of these properly? The runbook describes the Bradford Hill / trial-evidence workflow used on the assessment page, and handoff_top1000_signals.csv lists the strongest unassessed pairs across all drugs.
Common questions
What are the most reported side effects of Fondaparinux?
In FDA FAERS, the most frequently co-reported reaction terms for Fondaparinux are anaemia, haematoma, pulmonary embolism, haemorrhage, haemoglobin decreased, deep vein thrombosis. These are report counts, not rates: FAERS has no denominator, reporting is voluntary and uneven, and a term can be reported because of the illness being treated rather than the drug.
Does Fondaparinux have an FDA boxed warning?
Yes. The current FDA label carries a boxed warning: SPINAL/EPIDURAL HEMATOMAS Epidural or spinal hematomas may occur in patients who are anticoagulated with low molecular weight heparins (LMWH), heparinoids, or fondaparinux sodium and are receiving neuraxial anesthesia or undergoing spinal puncture. These hematomas may result in long-term or permanent paralysis.
Do FAERS signals prove that Fondaparinux causes these side effects?
No. A disproportionality signal (PRR, ROR) means a reaction is reported more often with this drug than with others in the database. That can reflect a real effect, but also the disease being treated, stimulated reporting after news or litigation, co-medications, or how reports are coded. Causality needs temporality, dose-response, biological plausibility, consistency across data sources and, ideally, trial or cohort evidence. This page screens each term against the FDA label and ClinicalTrials.gov results; it does not establish causation.
Sources & methods
- FDA label via openFDA (set ID 4b65f642-87f7-4da5-a9c9-02cd1f8d9d16, effective 20241215; matched on
openfda.generic_name.exact:"FONDAPARINUX SODIUM") - Bayesian shrinkage measures computed offline over all 1,317,300 cached pairs: BCPNN information component (IC, with Norén closed-form IC025) and MGPS empirical-Bayes geometric mean (EBGM, EB05) with a two-component gamma prior fitted by maximum marginal likelihood (α₁=0.57, β₁=0.02, α₂=1.42, β₂=0.70, w=0.17); unstratified
- FAERS pair statistics from the OpenPV build of 2026-09-14 (openFDA
count=aggregation, fieldpatient.drug.openfda.generic_name.exact, 1,022 reaction terms, min 3 co-reports); PRR/ROR with 95% CI, chi-square with Yates correction - Serious-only and stratified counts (serious:1, patient.patientsex, primarysource.qualification) from openFDA count queries; serious-only PRR uses the drug serious report total and the term global serious total (N_serious=11,882,979); strata shown only when n ≥ 20
- Seriousness and sex counts from openFDA
count=serious,patient.patientsex,seriousnessdeath
Page generated 2026-10-08. Label and PubChem text are retrieved automatically and may lag the current label; always check the current prescribing information. OpenPV is a beta research tool of the Open Source Medicine Foundation.