This page shows what was measured, who it was measured in, and what that does not settle.
What Fondaparinux does in the body
Preventing and treating blood clots in the legs and lungs, given as a once-daily injection
Heparin is a long, ragged sugar chain, and only a short five-sugar stretch of it does the essential job: gripping a blood protein called antithrombin and forcing it into a shape that destroys the clotting enzyme factor Xa. Fondaparinux is that five-sugar stretch built from scratch in a factory, with none of the rest. Because it is too short to reach across and grab thrombin as well, it does one thing only, about 300 times faster than antithrombin manages alone. It is the same molecule in every vial, unlike the heparins, and it is cleared entirely by the kidneys.
What happened in people
Death or reinfarction at 30 days 9.7% against 11.2% in 12,092 ST-elevation myocardial infarction patients, with no benefit in the primary intervention subgroup
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
The recorded finding that sits closest to something a person would notice. Written into the record, not signed off, and it carries no population or interval.
Approved in the United States in December 2001 under NDA 021345, for venous thromboembolism only
Where it acts
Blood plasma, at the antithrombin III molecule circulating there — no cell is entered at any point
Kind of result
Living longer, or avoiding a major event
Supervision
RNAWiki has not recorded a supervision or regulatory status for this substance.
What the registries record it as
The substance registry classes this as chemical.
FDA substance registry · J177FOW5JL · read 2026-08-29
Where each sentence above came from
No recorded sentence describes the change this makes in a way that stands on its own. The page opens with what it is taken for instead, and the recorded explanation follows below.
Shown as the opening line on this page.
A limit recorded against this substance. Not signed off as a reviewed claim.
The four opening statements run to 142 words.
Words this page uses
Four words worth knowing first
Chosen from what this page shows, with each one explained before the word it depends on.
Comparator
A comparator is whatever the treatment was measured against.
A picture of it, and where the picture fails
It is like the other runner in a race.
Where that stops being true. A race has one winner. A study can show both arms improved.
What people get wrong. Results are read without asking what the other group got. Beating nothing is not beating a treatment.
The control condition against which the experimental intervention is assessed.
Randomisation
Randomisation means chance decides who gets which treatment.
A picture of it, and where the picture fails
It is like a coin toss deciding the groups.
Where that stops being true. A coin toss is fair once. Fairness here comes from doing it for everyone.
What people get wrong. It is thought to make groups identical. It makes them similar on average, including on things nobody measured.
Allocation of participants to arms by a chance process, so that unmeasured factors are balanced in expectation.
Absolute difference
An absolute difference is how many more people in a hundred were affected.
A picture of it, and where the picture fails
It is like counting heads in two rooms of a hundred.
Where that stops being true. Heads are easy to count. Study results carry a margin of error too.
What people get wrong. It is confused with a percentage change, which can look far larger.
The arithmetic difference in event rates between arms.
Confidence interval
A confidence interval is the range the true answer is likely to sit in.
A picture of it, and where the picture fails
It is like a weather forecast giving a range rather than one number.
Where that stops being true. A forecast range covers tomorrow. This one covers what the study could resolve.
What people get wrong. The middle number is read as the answer. A range crossing zero means no change is still possible.
An interval estimate that would contain the true parameter in a stated proportion of repeated studies.
What happened in people◇Read from sources, not yet reviewed
What happened in people
Each card is one study: the exact question it asked, who was in it, and whether it showed what it set out to show.
Venous thromboembolism to day 11 by mandatory bilateral venography or documented symptomatic event, fondaparinux 2.5 mg daily versus approved enoxaparin regimens
✓ The study showed what it set out to show
Who was studied
Orthopaedic surgery programme (4 randomised double-blind trials, pooled)
How many people
7344
Study design
Phase 3, four multicentre randomised double-blind trials analysed together
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
6.8% (182/2682) vs 13.7% (371/2703), common odds reduction 55.2% (95% CI 45.8% to 63.1%), p<0.001
Repeated elsewhere
Replicated
What this does not prove. Meeting one endpoint in one population does not carry to other goals or other people.
The limits of this study, and where it came from
Main limit. Major bleeding was significantly more frequent on fondaparinux (p=0.008), though bleeding causing death, reoperation or critical-organ involvement did not differ. Most primary events were asymptomatic venographic clots rather than clinical ones.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Subcutaneous injection from a single-dose prefilled syringe, once daily
Interval reported. 95% CI 45
Written into the record, not signed off as a reviewed claim.
Death, myocardial infarction or refractory ischaemia at nine days, fondaparinux versus enoxaparin in acute coronary syndromes
✓ The study showed what it set out to show
Who was studied
OASIS-5 (NCT00139815)
How many people
20078
Study design
Phase 3 randomised double-blind non-inferiority trial, mean 6 days of treatment
Compared against
Not recorded for this study
Kind of result
Living longer, or avoiding a major event
What was found
5.8% vs 5.7%, HR 1.01 (95% CI 0.90 to 1.13), meeting non-inferiority. Major bleeding 2.2% vs 4.1%, HR 0.52, p<0.001. Deaths at 30 days 295 vs 352, p=0.02
Repeated elsewhere
Unreplicated
What this does not prove. Meeting one endpoint in one population does not carry to other goals or other people.
The limits of this study, and where it came from
Main limit. Catheter thrombus during percutaneous coronary intervention 0.9% on fondaparinux against 0.4% on enoxaparin, requiring unfractionated heparin to be added back at the time of the procedure.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Subcutaneous injection from a single-dose prefilled syringe, once daily
Interval reported. 95% CI 0
Written into the record, not signed off as a reviewed claim.
Death or reinfarction at 30 days, fondaparinux versus usual care in ST-elevation myocardial infarction
✓ The study showed what it set out to show
Who was studied
OASIS-6 (NCT00064428)
How many people
12092
Study design
Phase 3 randomised double-blind trial, up to 8 days of treatment, 30-day endpoint
Compared against
Not recorded for this study
Kind of result
Living longer, or avoiding a major event
What was found
9.7% (585/6036) vs 11.2% (677/6056), HR 0.86 (95% CI 0.77 to 0.96), p=0.008, absolute risk reduction 1.5 percentage points
Repeated elsewhere
Unreplicated
What this does not prove. Meeting one endpoint in one population does not carry to other goals or other people.
The limits of this study, and where it came from
Main limit. No benefit in patients undergoing primary percutaneous coronary intervention. The control arm differed between strata — placebo in one, unfractionated heparin for 48 hours in the other — so the trial compares fondaparinux against two different things at once.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Subcutaneous injection from a single-dose prefilled syringe, once daily
Interval reported. 95% CI 0
Written into the record, not signed off as a reviewed claim.
Composite of major bleeding, minor bleeding or major vascular access-site complications up to 48 hours after percutaneous coronary intervention, low-dose versus standard-dose unfractionated heparin in fondaparinux-treated patients
✗ The study did not show it
Who was studied
FUTURA/OASIS-8 (NCT00790907)
How many people
2026
Study design
Phase 4 randomised double-blind parallel-group trial nested in a cohort of 3,235
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
4.7% vs 5.8%, odds ratio 0.80 (95% CI 0.54 to 1.19), p=0.27
Repeated elsewhere
Unreplicated
What this does not prove. A study that did not show an effect does not show that no effect exists anywhere.
The limits of this study, and where it came from
Main limit. The key secondary outcome favoured the standard dose: 5.8% vs 3.9%, odds ratio 1.51 (95% CI 1.00 to 2.28), p=0.05; death, myocardial infarction or target vessel revascularisation 4.5% vs 2.9%, odds ratio 1.58 (0.98 to 2.53), p=0.06.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Subcutaneous injection from a single-dose prefilled syringe, once daily
Interval reported. 95% CI 0
Written into the record, not signed off as a reviewed claim.
Symptomatic recurrent pulmonary embolism or new or recurrent deep vein thrombosis at three months, fondaparinux versus intravenous unfractionated heparin
3.8% (42/1103) vs 5.0% (56/1110), absolute difference -1.2 percentage points (95% CI -3.0 to 0.5), meeting non-inferiority
Repeated elsewhere
Partially Replicated
What this does not prove. Meeting one endpoint in one population does not carry to other goals or other people.
The limits of this study, and where it came from
Main limit. Open-label design. Major bleeding 1.3% vs 1.1%. Haemodynamically unstable patients were excluded, so the result does not describe massive pulmonary embolism.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Subcutaneous injection from a single-dose prefilled syringe, once daily
Interval reported. 95% CI -3
Written into the record, not signed off as a reviewed claim.
RNAWiki holds 5 written-up human studies for this substance, each with the question it asked.
How we know it
Each card names the study, the number of people and what the study set out to measure.
What this does not prove
These summaries were written by a person and have not been signed off as reviewed claims.
Why it matters
A study that failed is as informative as one that worked, and both are here.
What we still do not know
No reviewed claim exists, so no exact population, effect size or interval is published yet.
What it changes in the body◇Read from sources, not yet reviewed
The path through the body
From what a person takes to what changes. A solid line is a step measured in people. A dashed line is a step nobody has measured that way.
Start
Fondaparinux
What a person takes: Subcutaneous injection from a single-dose prefilled syringe, once daily.
The measurement behind this step
Prefilled syringes with an automatic needle-guard system, injected once daily into subcutaneous tissue. Bioavailability is essentially complete and the 17 to 21 hour half-life supports a single daily dose with no coagulation monitoring. The needle guard contains dry natural rubber, which the label flags as a latex allergy risk. Neither the activated partial thromboplastin time nor the prothrombin time measures this drug; a fondaparinux-calibrated anti-factor Xa assay is required.
Getting in
One fixed injection, the same molecule in every vial
A single daily injection under the skin. Unlike heparin, which is a mixture of thousands of different chains, every dose of this is exactly the same compound.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
A fully synthetic methylated pentasaccharide, C31H53N3O49S8, 1508.30 g/mol as the free acid, dispensed as the sodium salt. Subcutaneous bioavailability is essentially complete and the elimination half-life is 17 to 21 hours, which is what permits once-daily dosing without monitoring.
It never enters a cell. It finds a protein already floating in the blood, antithrombin, and binds to one specific site on it.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
The pentasaccharide is the minimal high-affinity antithrombin-binding sequence isolated from heparin, with the sulfation pattern that binding requires. Every sugar and every sulfate in the molecule is there because the antithrombin site needs it; nothing in it is structural padding.
Antithrombin changes shape and speeds up about three hundred times
Binding forces antithrombin into an active shape. It then destroys the clotting enzyme factor Xa roughly three hundred times faster than it would on its own.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
The label states the potentiation directly: fondaparinux "potentiates (about 300 times) the innate neutralization of Factor Xa by ATIII". The conformational change expels antithrombin’s reactive centre loop, converting it from a slow substrate-like inhibitor into a fast one. Fondaparinux dissociates intact afterwards and catalyses again.
Thrombin is left completely alone — and that is the whole trade
Too short to reach thrombin, this drug does one job only. That is why it bleeds less, and also why clots can still form on a plastic catheter inside an artery.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
Inactivating thrombin requires a chain long enough to bridge antithrombin and thrombin in a ternary complex, roughly 18 saccharide units. A pentasaccharide cannot. The label confirms the consequences: no thrombin inactivation, no known effect on platelet function, no effect on fibrinolytic activity or bleeding time at recommended doses. Contact activation on a foreign surface generates thrombin directly, which is the mechanism behind the 0.9% catheter thrombus rate in OASIS-5.
Fewer clots, less bleeding, and only one way out of the body
Half the clots of enoxaparin after joint surgery and half the serious bleeding in heart attack care. It leaves only through the kidneys, and there is no antidote.
──Measured in people. Written by a person from the study named beside the step. Not signed off as a reviewed claim.
The measurement behind this step
Venous thromboembolism 6.8% against 13.7% on enoxaparin after major orthopaedic surgery; major bleeding 2.2% against 4.1% in acute coronary syndromes. Clearance is entirely renal as unchanged drug, so a creatinine clearance below 30 mL/min is a contraindication rather than a dose reduction, and body weight below 50 kg contraindicates adult venous thromboembolism prophylaxis. Protamine does not reverse it.
No suggested links are held for this record, so nothing is hidden from this path.
What we know
The record describes 5 steps from taking it to an effect in a person.
How we know it
Each step names the study behind it in the technical detail beside it.
What this does not prove
A change inside the body is a reason to look. It is not a result in a person.
Why it matters
A reader can see exactly where the chain stops being measured in people.
What we still do not know
No reviewed claim binds any of these steps to a named population.
What is missing or unclear◇Read from sources, not yet reviewed
Were people like you studied?
RNAWiki cannot tell whether a study fits you. It can show who was in it, and where the result stops carrying.
Who was studied
People similar to this profile were included.
Adults having hip fracture, hip replacement, knee replacement or abdominal surgery, adults being treated for a leg or lung clot, and children over 1 year and 10 kg with venous thromboembolism. It is also used off label as an anticoagulant in heparin-induced thrombocytopenia, which is not an approved indication in the United States.
Who is missing from the studies
Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
What the label states about particular groups
On pediatric, the label states: “Safety and effectiveness of fondaparinux sodium in pediatric patients have not been established.”
US prescribing information · 49e0d7bc-3f49-849b-c77c-98682d1c0d19 · read 2026-08-30
On older people, the label states: “In clinical trials the efficacy of fondaparinux sodium in the elderly (65 years or older) was similar to that seen in patients younger than 65 years; however, serious adverse events increased with age.”
US prescribing information · 49e0d7bc-3f49-849b-c77c-98682d1c0d19 · read 2026-08-30
On people who are pregnant, the label states: “Risk Summary Available data from published literature and postmarketing reports have not reported a clear association with fondaparinux sodium and adverse developmental outcomes.”
US prescribing information · 49e0d7bc-3f49-849b-c77c-98682d1c0d19 · read 2026-08-30
On people who are breastfeeding, the label states: “Risk Summary There are no data on the presence of fondaparinux sodium in human milk, or the effects on milk production.”
US prescribing information · 49e0d7bc-3f49-849b-c77c-98682d1c0d19 · read 2026-08-30
On people with reduced liver function, the label states: “Following a single, subcutaneous dose of 7.5 mg of fondaparinux sodium in patients with moderate hepatic impairment (Child-Pugh Category B) compared to subjects with normal liver function, changes from baseline in aPTT, PT/INR, and antithrombin III were similar in the two groups.”
US prescribing information · 49e0d7bc-3f49-849b-c77c-98682d1c0d19 · read 2026-08-30
On people with reduced kidney function, the label states: “Patients with impaired renal function are at increased risk of bleeding due to reduced clearance of fondaparinux sodium [see Contraindications (4) and Warnings and Precautions ( 5.3 ) ].”
US prescribing information · 49e0d7bc-3f49-849b-c77c-98682d1c0d19 · read 2026-08-30
Where the result stopped carrying
Catheter thrombosis during percutaneous coronary intervention, at more than twice the enoxaparin rate, requiring unfractionated heparin to be added back
Absence of any benefit in the primary percutaneous coronary intervention subgroup of OASIS-6
FUTURA/OASIS-8, which missed its primary endpoint (p=0.27) and produced a secondary signal favouring the higher heparin dose
Major bleeding against enoxaparin in the orthopaedic programme, p=0.008
This is a scope explorer, not a diagnosis engine.
It shows who was studied so you can see whether people similar to you were included.
RNAWiki cannot tell whether a study fits you. It can show who was in it.
What it would be like to take◇Read from sources, not yet reviewed
Why it might seem to do nothing
A real effect and a noticed effect are different things. These are the recorded reasons the two come apart.
It was studied in different people
The people in the studies were not much like the reader.
On this record: Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
The evidence may simply be wrong
Small early studies often do not hold up.
On this record: RNAWiki has not yet published a reviewed conclusion for this use.
Other reasons RNAWiki checked and found nothing for (11)
It was studied for a different goal
The studies measured something else entirely. Nothing in this record points to this reason.
A different form was studied
The studied form is not the form on the shelf. Nothing in this record points to this reason.
There was nothing to correct
Where a level is already normal, topping it up may change nothing. Nothing in this record points to this reason.
Something else had to happen too
In the studies it was paired with training, a diet or another treatment. Nothing in this record points to this reason.
The change is too small to feel
A real change can still sit below what a person notices. Nothing in this record points to this reason.
Day-to-day swing hides it
Sleep, food, stress and time of day move most numbers more than this would. Nothing in this record points to this reason.
Not enough time yet
The studies ran longer than the person has waited. Nothing in this record points to this reason.
It was not taken as studied
Missed days change the result, and studies count them. Nothing in this record points to this reason.
Something else changed at the same time
Two changes at once cannot be told apart afterwards. Nothing in this record points to this reason.
The product may not be what it says
Contents of a sold product are not always what the label states. Nothing in this record points to this reason.
No recorded reason
RNAWiki has nothing stored that would explain it. Nothing in this record points to this reason.
None of these is a reason to take more. Taking more is not a step this page ever suggests.
What it would be like to take◇Read from sources, not yet reviewed
What taking it involves
The recorded facts about getting hold of it and using it. Nothing here is a suggestion about what you should do.
How it is supplied
Given by a clinician
❝ Quoted from a source
Where this came from
Copied from a source RNAWiki stored, with the source named.
Read from the recorded approval status.
No source is stored against this line.
Form and route
Subcutaneous injection from a single-dose prefilled syringe, once daily
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
The form and route recorded on this substance.
No source is stored against this line.
Who oversees it
RNAWiki has not recorded a supervision or regulatory status for this substance.
❝ Quoted from a source
Where this came from
Copied from a source RNAWiki stored, with the source named.
No register row and no identity class settled the question.
No source is stored against this line.
What is in the pack
Prefilled syringes with an automatic needle-guard system, injected once daily into subcutaneous tissue. Bioavailability is essentially complete and the 17 to 21 hour half-life supports a single daily dose with no coagulation monitoring. The needle guard contains dry natural rubber, which the label flags as a latex allergy risk. Neither the activated partial thromboplastin time nor the prothrombin time measures this drug; a fondaparinux-calibrated anti-factor Xa assay is required.
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
Recorded notes on how this is sold and what that means for what is in the pack.
No source is stored against this line.
Where it is registered
Regulatory records are listed in the technical disclosure at the foot of this page.
# Counted from records
Where this came from
A count of rows RNAWiki holds. It describes our records, not your body.
Register entries are stored per jurisdiction and shown with their dates.
No source is stored against this line.
Why people stop
Not recorded.
∅ Nothing recorded
Where this came from
RNAWiki holds nothing here and says so rather than guessing.
No record of why people stopped taking it is stored for this substance.
No source is stored against this line.
What it would be like to take◇Read from sources, not yet reviewed
What can go wrong
Sorted by where each line came from. A regulator's label and a report somebody sent in are not the same kind of fact.
·Worth asking a clinician aboutWritten into the record from the studies named on this page
The United States label carries a boxed warning on spinal and epidural haematoma with neuraxial anaesthesia or spinal puncture, which can cause long-term or permanent paralysis. Contraindications are severe renal impairment below a creatinine clearance of 30 mL/min, active major bleeding, bacterial endocarditis, thrombocytopenia with a positive in vitro anti-platelet antibody test in the presence of fondaparinux, body weight below 50 kg for adult venous thromboembolism prophylaxis, and prior serious hypersensitivity. Clearance is entirely renal and there is no reversal agent — protamine does not work. Thrombocytopenia can occur, and periodic blood counts, serum creatinine and faecal occult blood testing are recommended.
Nobody counted how many people took this and were fine, so this cannot be turned into a rate.
Over a long time. No completed tested study window is recorded, so long-term effects are not established by the registry record.
Groups the studies covered thinly. Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
What is missing or unclear◇Read from sources, not yet reviewed
Does the exact form matter?
Evidence belongs to the exact thing that was tested. A different salt, a different mixture or a different preparation is a different question.
The form that was studied
Subcutaneous injection from a single-dose prefilled syringe, once daily
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
The form used in the studies cited on this page.
No source is stored against this line.
What is sold
Bioavailability is essentially complete and the 17 to 21 hour half-life supports a single daily dose with no coagulation monitoring. The needle guard contains dry natural rubber, which the label flags as a latex allergy risk. Neither the activated partial thromboplastin time nor the prothrombin time measures this drug; a fondaparinux-calibrated anti-factor Xa assay is required.
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
Recorded notes on which forms are sold and how they compare.
No source is stored against this line.
What is recorded as being sold
33 products list this as an active ingredient in the United States drug directory. 33 of them contain it and nothing else.
FDA National Drug Code directory · 0781-3454 · read 2026-08-29
They are sold as injection, injection, solution and powder, taken subcutaneous.
FDA National Drug Code directory · 0781-3454 · read 2026-08-29
The regulator's established pharmacologic class for it is factor xa inhibitor [epc] and factor xa inhibitors [moa].
FDA National Drug Code directory · 0781-3454 · read 2026-08-29
7 published labels name it as an active ingredient. 7 of them describe this substance alone, which is where its own label text on this page comes from.
US prescribing information · 49e0d7bc-3f49-849b-c77c-98682d1c0d19 · read 2026-08-29
Those labels are classed as human prescription drug.
US prescribing information · 49e0d7bc-3f49-849b-c77c-98682d1c0d19 · read 2026-08-29
Fondaparinux Sodium is subcutaneous at 3 DOSAGE FORMS AND STRENGTHS Single-dose, prefilled syringes containing either 2.5 mg, 5 mg, 7.5 mg, or 10 mg of fondaparinux sodium., recorded as fda label in effect 2021-09-10 in the United States.
US prescribing information · 49e0d7bc-3f49-849b-c77c-98682d1c0d19 · read 2026-08-30
Recorded price in US: 12.25578–55.3125 USD per one millilitre, across 22 priced products whose strengths and pack forms differ, as of 2026-08-26, paid by retail pharmacies buying the product, as surveyed by the Centers for Medicare & Medicaid Services. It is not a list price, an insurance price, or what anyone pays at a counter..
Recorded source · 2026-08-26 · read 2026-08-28
Evidence carries across two names for one substance. It does not carry across a salt, a mirror form or a mixture.
What it would be like to take◇Read from sources, not yet reviewed
What you could measure
This one is decided with a clinician, so this section holds questions to ask rather than a plan to run.
RNAWiki could not confidently classify this substance, so no self-experiment plan is offered.
Questions worth asking
Which of the trials of Fondaparinux studied people like me?
What was measured, and for how long?
Was the result a laboratory value or a health outcome?
What would we watch for, and when would we stop?
Tracking can show whether something changed for you. It cannot show what caused it.
RNAWiki records evidence. It does not say whether this substance is right for you.
What is missing or unclear◇Read from sources, not yet reviewed
Claims that go past the evidence
Things said about this substance that sound reasonable, and the exact step that is missing between the evidence and the claim.
✗Goes past the evidence
That halving venographic clots after joint surgery halves clinical harm — most events were asymptomatic screening findings and major bleeding rose
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
✗Goes past the evidence
That the mortality benefit in OASIS-5 is an anti-ischaemic effect — the ischaemic endpoint was a dead heat and the bleeding endpoint was not
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
✗Goes past the evidence
That fondaparinux is safe in heparin-induced thrombocytopenia — a sound structural argument supported by observational series, with no approved indication and no randomised trial
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
✗Goes past the evidence
That the United States label reflects the weight of evidence — the two largest positive trials are in an indication the label does not carry
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
What is missing or unclear◇Read from sources, not yet reviewed
What nobody knows yet
Open questions, each with why it is open and what would close it.
Missing populations
Which groups were under-represented in the studies has not been recorded.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Missing long-term data
No completed tested study window is recorded.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
No reviewed conclusion
RNAWiki has not yet published a reviewed conclusion for this use.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Missing interaction studies
No interaction was found in the registers checked. Not finding one is not the same as showing there is none.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Formulation uncertainty
Several salts, forms or products of Fondaparinux are recorded. Results from one form may not transfer to another.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Mechanism not reviewed
No reviewed mechanism story exists for this substance.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
What happened in people◇Read from sources, not yet reviewed
Check any of this yourself
Every line above traced back to the study it came from. This is the technical layer, and the vocabulary changes here.
Every line above can be traced to the study named beside it. Follow the link and read it.
Orthopaedic surgery: venous thromboembolism halved against enoxaparin in 7,344 patients
In plain words
Across four double-blind trials in hip and knee surgery, fondaparinux prevented about half the clots that enoxaparin allowed. The clots were looked for with imaging in everyone, not only in people with symptoms.
What was measured
Venous thromboembolism by day 11 on mandatory bilateral venography, and major bleeding
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
A meta-analysis of four multicentre randomised double-blind trials in 7,344 patients undergoing elective hip replacement, elective major knee surgery or hip fracture surgery compared fondaparinux 2.5 mg once daily started six hours after surgery with approved enoxaparin regimens. Venous thromboembolism by day 11 — defined as deep vein thrombosis on mandatory bilateral venography, or documented symptomatic deep vein thrombosis or pulmonary embolism — occurred in 182 of 2,682 fondaparinux patients (6.8%) against 371 of 2,703 enoxaparin patients (13.7%), a common odds reduction of 55.2% (95% CI 45.8% to 63.1%, p<0.001), consistent across all surgery types and subgroups. Major bleeding was significantly more frequent on fondaparinux (p=0.008), while bleeding that led to death or reoperation or occurred in a critical organ did not differ between the groups. The mandatory venography matters: most of these events were asymptomatic clots found because the protocol went looking, not clinical events.
Written into the record, not signed off as a reviewed claim
OASIS-5: half the major bleeding of enoxaparin, and fewer deaths, in 20,078 patients
In plain words
In the largest trial ever to compare two injected anticoagulants in heart attack care, the two prevented the same number of heart events, but fondaparinux caused half as many serious bleeds and fewer people died within a month.
What was measured
Major bleeding at nine days, 2.2% against 4.1%, and 30-day mortality, 295 deaths against 352
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
OASIS-5 (NCT00139815) randomised 20,078 acute coronary syndrome patients to fondaparinux 2.5 mg once daily or enoxaparin 1 mg/kg twice daily for a mean of six days. Death, myocardial infarction or refractory ischaemia at nine days occurred in 5.8% against 5.7% (hazard ratio 1.01, 95% CI 0.90 to 1.13), meeting non-inferiority. Major bleeding at nine days was 2.2% against 4.1% (hazard ratio 0.52, p<0.001). The composite of the primary outcome and major bleeding favoured fondaparinux, 7.3% against 9.0% (hazard ratio 0.81, p<0.001). Deaths at 30 days were 295 against 352 (p=0.02) and at 180 days 574 against 638 (p=0.05). The mortality difference is best read as a downstream consequence of the bleeding difference rather than as an anti-ischaemic effect, because the ischaemic endpoint itself was a dead heat.
Written into the record, not signed off as a reviewed claim
Catheter thrombosis: clots formed on the guiding catheter at more than twice the rate
In plain words
During coronary procedures, clots formed on the plastic catheter inside the artery in about 1 patient in 110 on fondaparinux, against 1 in 250 on enoxaparin. Giving ordinary heparin alongside it largely prevented this.
What was measured
Catheter thrombus during percutaneous coronary intervention, 0.9% on fondaparinux against 0.4% on enoxaparin
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
In the prospectively planned percutaneous coronary intervention analysis of OASIS-5, covering 12,715 patients catheterised and 6,238 who underwent intervention, catheter thrombus occurred in 0.9% of fondaparinux patients against 0.4% of those on enoxaparin alone. The same analysis showed fondaparinux more than halving major bleeding around the procedure — 2.4% against 5.1% at day 9, hazard ratio 0.46, p<0.00001 — with superior net clinical benefit (8.2% against 10.4%, hazard ratio 0.78, p=0.004). The mechanism is straightforward and is the mirror image of the drug’s selling point: fondaparinux does nothing to thrombin, and the contact activation that occurs on a foreign surface generates thrombin directly. Adding unfractionated heparin at the time of the procedure largely prevented the catheter thrombi without increasing bleeding. A drug whose defining virtue is that it does one thing only has a failure mode in the one situation where the other thing matters.
Written into the record, not signed off as a reviewed claim
OASIS-6: death or reinfarction fell in ST-elevation myocardial infarction, except in primary PCI
In plain words
In 12,092 heart attack patients, fondaparinux reduced death or repeat heart attack from 11.2% to 9.7%. The benefit was absent in the group taken straight for a stent.
What was measured
Death or reinfarction at 30 days overall, and the absence of benefit in the primary percutaneous coronary intervention subgroup
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
OASIS-6 (NCT00064428) randomised 12,092 ST-elevation myocardial infarction patients across 447 hospitals in 41 countries to fondaparinux 2.5 mg daily for up to eight days or to usual care — placebo where unfractionated heparin was not indicated (stratum 1), or unfractionated heparin for up to 48 hours followed by placebo (stratum 2). Death or reinfarction at 30 days fell from 677 of 6,056 (11.2%) to 585 of 6,036 (9.7%), hazard ratio 0.86 (95% CI 0.77 to 0.96, p=0.008), absolute risk reduction 1.5 percentage points. There was no heterogeneity between the two strata, and there were significantly fewer episodes of cardiac tamponade at nine days (28 against 48, p=0.02). But the abstract states plainly that "there was no benefit in those undergoing primary percutaneous coronary intervention", and the benefit was concentrated in those receiving thrombolysis (hazard ratio 0.79, p=0.003) or no reperfusion at all (0.80, p=0.03). The same procedural gap that produced the catheter thrombi in OASIS-5 appears here as an absent treatment effect.
Written into the record, not signed off as a reviewed claim
FUTURA/OASIS-8 tried to fix the catheter problem with a lower heparin dose, and did not
In plain words
Since heparin had to be added back during the procedure, a trial asked whether a lower dose of it would bleed less. It did not, and the low-dose group had a numerically worse rate of death and heart attacks.
What was measured
Composite of major bleeding, minor bleeding or major vascular access-site complications up to 48 hours after intervention
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
FUTURA/OASIS-8 (NCT00790907) randomised 2,026 patients undergoing percutaneous coronary intervention within 72 hours, nested in a cohort of 3,235 high-risk non-ST-elevation acute coronary syndrome patients initially treated with fondaparinux, to low-dose unfractionated heparin 50 U/kg or standard-dose 85 U/kg adjusted by blinded activated clotting time. The primary composite of major bleeding, minor bleeding or major vascular access-site complications up to 48 hours occurred in 4.7% against 5.8% (odds ratio 0.80, 95% CI 0.54 to 1.19, p=0.27) — a clear miss. Major bleeding did not differ; only minor bleeding fell, 0.7% against 1.7% (odds ratio 0.40, p=0.04). The key secondary outcome moved the wrong way: 5.8% against 3.9% (odds ratio 1.51, 95% CI 1.00 to 2.28, p=0.05), and death, myocardial infarction or target vessel revascularisation 4.5% against 2.9% (odds ratio 1.58, 95% CI 0.98 to 2.53, p=0.06). Catheter thrombus rates were low in both arms, 0.5% and 0.1% (p=0.15). So the workaround for fondaparinux’s procedural weakness could not itself be optimised downwards, and the trial that tried it produced a signal pointing the other way.
Written into the record, not signed off as a reviewed claim
It won two 12,000-plus-patient coronary trials and has no United States coronary indication
In plain words
The two largest trials this drug has ever been in were both in heart attack patients, and both were positive. Neither appears in the American label, which covers only leg and lung clots.
What was measured
That an approved label is a summary of a drug’s evidence — for fondaparinux the two largest positive trials sit entirely outside the United States indications
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The United States prescribing information for ARIXTRA lists four indications: deep vein thrombosis prophylaxis in hip fracture, hip replacement, knee replacement and abdominal surgery; treatment of deep vein thrombosis; treatment of acute pulmonary embolism with warfarin; and treatment of venous thromboembolism in paediatric patients aged 1 year or older weighing at least 10 kg. Acute coronary syndrome appears nowhere in it, despite OASIS-5 (20,078 patients, major bleeding halved against enoxaparin, 30-day mortality significantly lower) and OASIS-6 (12,092 patients, death or reinfarction reduced from 11.2% to 9.7%). European guidance took a different view and fondaparinux carries an acute coronary syndrome recommendation there. The point of this entry is not that either regulator was wrong; it is that a reader who assumes the label summarises the evidence will be missing the two largest trials this drug has.
Written into the record, not signed off as a reviewed claim
Pulmonary embolism: a once-daily injection matched a monitored heparin infusion
In plain words
In 2,213 people with a clot in the lungs, a single daily injection worked as well as a continuous heparin drip with regular blood tests, and one in seven of them was treated partly at home.
What was measured
Symptomatic recurrent pulmonary embolism or new deep vein thrombosis at three months, and major bleeding
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The MATISSE-PE trial randomised 2,213 patients with acute symptomatic pulmonary embolism, open-label, to weight-banded subcutaneous fondaparinux once daily or to a continuous intravenous unfractionated heparin infusion adjusted to an activated partial thromboplastin time ratio of 1.5 to 2.5, both continued at least five days and until the international normalised ratio exceeded 2.0 on a vitamin K antagonist. Recurrent thromboembolic events at three months occurred in 42 of 1,103 fondaparinux patients (3.8%) against 56 of 1,110 heparin patients (5.0%), absolute difference -1.2 percentage points (95% CI -3.0 to 0.5). Major bleeding was 1.3% against 1.1% and three-month mortality was similar. 14.5% of fondaparinux patients received part of their treatment as outpatients, which was the practical point of the trial as much as the efficacy result was.
Written into the record, not signed off as a reviewed claim
Used routinely in heparin-induced thrombocytopenia, approved for it nowhere
In plain words
Because it is a synthetic fragment rather than a heparin, this drug is widely used when a patient has had the immune reaction to heparin. That use has never been approved and rests on small studies.
What was measured
That structural inability to form heparin–platelet factor 4 complexes establishes clinical safety in heparin-induced thrombocytopenia — a mechanistic argument supported by observational series, with no approved indication and no randomised outcome trial
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Fondaparinux is too short to form the heparin–platelet factor 4 complexes that the heparin-induced thrombocytopenia antibody recognises, which is a genuine structural argument and the reason for the practice. The United States label does not carry the indication, and the direct thrombin inhibitors argatroban and bivalirudin are the agents with approved or established roles there. The label’s own statement is narrower than the practice and is often misquoted: fondaparinux is contraindicated in "thrombocytopenia associated with a positive in vitro test for anti-platelet antibody in the presence of fondaparinux sodium" — that is, in the rare case where the antibody reacts to fondaparinux itself, not in heparin-induced thrombocytopenia generally. The evidence base for the off-label use is observational series and small comparisons, not a randomised outcome trial, and the absence of any reversal agent in a patient population already prone to bleeding is the reason that gap matters.
Source
ARIXTRA (fondaparinux sodium) injection, United States prescribing information, sections 1 and 4
Role in the trial
Not matched to a registered study
Identity check
no open identity hold
Audit mark
caution
Review state
Written into the record, not signed off as a reviewed claim
How many documents were read
7 documents were read for this substance.
RNAWiki source record
7 of them state the same bioavailability, and they agree.
RNAWiki source record
Where else this substance is registered
FDA substance identifier (UNII)
J177FOW5JL
CAS registry number
104993-28-4
PubChem compound
5282448
RxNorm concept
321208
EMA substance identifier
100000090128
DrugBank
DB00569
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Every public sentence names a source
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Trial roles classified for highlighted evidence
No registered study is classified as testing this substance.
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Safety mode resolved
No register row and no identity class settled the question.
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Canonical metadata present
slug and display name present
What is missing or unclear◇Read from sources, not yet reviewed
How this medicine reached us
Kept near the foot of the page. A historical event moves up only when it changes something about this substance today.
What the approval register records
7 approved applications cover products containing this substance. The earliest was NDA021345, approved 20011207 to MYLAN IRELAND LTD.
This order is fixed in code and does not count clicks or time on the page.
What is not here
7 questions this page could not answer
These sections were prepared and left out because there was nothing to put in them. They are listed rather than hidden, so the gaps in this record are visible.
What was measured, goal by goal — found nothing in the sources checked.
How close this is to real life — found nothing in the sources checked.
Felt, measured, or meaningful — found nothing in the sources checked.
How long anything takes — found nothing in the sources checked.
What it may clash with — found nothing in the sources checked.
Other ways to the same goal — found nothing in the sources checked.
What changed on this page — found nothing in the sources checked.
The record as stored
The full record, for auditing
Everything above is built from what is below. This layer keeps the technical vocabulary, record identifiers and every stored row, so a reader who wants to check the page can.
The older medicine-wide conclusion held in this record
Written for a clinical reader, and about the medicine as a whole rather than about one indication, population and set of trials. RNAWiki does not treat it as a programme conclusion and no reviewer has signed it off in that form. It is here word for word because it is what the record holds.
The synthetic five-sugar fragment of heparin, which cut venous thromboembolism after major orthopaedic surgery from 13.7% to 6.8% against enoxaparin in 7,344 patients and halved major bleeding against enoxaparin in 20,078 acute coronary syndrome patients — while causing catheter thrombosis during coronary intervention, and while never receiving a United States coronary indication at all.
Recorded evidence blocks (11)
Q1
On the Fondaparinux label: indicated for what?
"Fondaparinux sodium injection is a Factor Xa inhibitor (anticoagulant) indicated for: Prophylaxis of deep vein thrombosis (DVT) in patients undergoing hip fracture surgery (including extended prophylaxis), hip replacement surgery, knee replacement surgery, or abdominal surgery. ( 1.1 ) Treatment of DVT or acute…": indications and usage on Fondaparinux's label. DailyMed label · dffbf7c9-495e-4a33-ac76-57b52f014fc2 · 2025-10-28
Q2
60 registered trials of Fondaparinux — at which phases?
Registered studies posting no result
35 of 60
60 registered studies of Fondaparinux: 18 phase3, 12 na or unstated, 10 phase4, 8 na, 8 phase2, 5 phase1, 1 early phase1. CLINICALTRIALS_SNAPSHOT · 2026-09-01
128 with a PubMed record
Show the evidence
phase3
18
na or unstated
12
phase4
10
na
8
phase2
8
phase1
5
7 more recorded rows
early phase1
1
completed
38
terminated
10
withdrawn
7
unknown
3
not yet recruiting
1
recruiting
1
recorded 2026-09-01 · last checked 2026-09-04
Q3
17 of Fondaparinux's trials stopped: accrual/recruitment, other?
17 to 21 hours; The elimination half-life is 17 to 21 hours.
bioavailabilitypharmacokinetics
100 %; Absorption: Fondaparinux sodium administered by subcutaneous injection is rapidly and completely absorbed (absolute bioavailability is 100%).
metabolismpharmacokinetics
Metabolism: In vivo metabolism of fondaparinux has not been investigated since the majority of the administered dose is eliminated unchanged in urine in individuals with normal kidney function.
recorded 2025-10-28 · last checked 2026-09-04
Q6
Which running trial of Fondaparinux could settle lifespan?
NCT06710184 measures Composite endpoint of mortality, new myocardial infarction, and clinical deterioration resulting in acute CAG, reading out 2029-07-01.
1 open trial; n 5076; "Treatment With Aspirin Alone Versus Aspirin in Combination With Fondaparinux Before Early Coronary Assessment in Patients With Non-ST-Elevation Myocardial Infarction"
Show the evidence
TrialNCT06710184
"Treatment With Aspirin Alone Versus Aspirin in Combination With Fondaparinux Before Early Coronary Assessment in Patients With Non-ST-Elevation Myocardial Infarction"; n 5076; "Composite endpoint of mortality, new myocardial infarction, and clinical deterioration resulting in acute CAG"; 2029-07-01
Q7
Which 19 trials of Fondaparinux posted no result?
Posted no result
19 of 19 completed trials
Registrations
NCT00038961, NCT00139815, NCT00333021, NCT00413504, NCT00436787 and NCT01444612, and 13 more
Completion dates
oldest 2004-10; newest 2023-12-01
Show the evidence
Trial
NCT00038961
2004-10
NCT00139815
2005-12
NCT00333021
2007-02
NCT00413504
2007-07
NCT00436787
2007-12
NCT01444612
2010-11
13 further recorded trials
NCT01406301
2011-07
NCT01390896
2013-01
NCT01121770
2013-02
NCT01267305
2013-08
NCT00894283
2013-09
NCT01390883
2013-10
NCT00476216
2013-12
NCT01691495
2014-08
NCT01428531
2015-06
NCT01428544
2015-06
NCT01727427
2017-12
NCT04368377
2020-04-23
NCT05001776
2023-12-01
Q8
At the median, Fondaparinux's trials enrolled 79 people — anything larger?
Median enrolment
79
Largest enrolment
20078
Registered trials counted
60
Q9
What do 1363 spontaneous reports say about Fondaparinux — and not say?
These are reports people sent to a regulator. They do not show the medicine caused the reaction. Nobody counted how many people took the medicine and reported nothing. The same event can be reported more than once, and many reports are incomplete. News coverage, lawsuits and new warnings change how often people report. A count is not a rate and not a risk.
Fondaparinux appears in spontaneous reports to regulators. Across the 10 most-reported reaction terms, 1363 reaction mentions were counted: haematoma 264; anaemia 245; haemoglobin decreased 164; pulmonary embolism 128. FAERS via Open Targets · CHEMBL1200644 · 2026-06-24
Show the evidence
haematoma
264
anaemia
245
haemoglobin decreased
164
pulmonary embolism
128
haemorrhage
121
deep vein thrombosis
99
4 more recorded rows
muscle haemorrhage
97
melaena
92
thrombocytopenia
82
post procedural haemorrhage
71
recorded 2026-06-24 · last checked 2026-09-04
Q10
Which 10 reactions does Fondaparinux's label not list?
[See Warnings and Precautions ( 5.2 ).] In an in vitro study in human liver microsomes, inhibition of CYP2A6 hydroxylation of coumarin by fondaparinux (200 micromolar i.e., 350 mg/L) was 17 to 28%.
drug_interactions
Since fondaparinux does not markedly inhibit CYP450s (CYP1A2, CYP2A6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, or CYP3A4) in vitro, fondaparinux sodium is not expected to significantly interact with other drugs in vivo by inhibition of metabolism mediated by these isozymes.
ChEMBL 37 — CC BY-SA 3.0 Unported · ClinicalTrials.gov — US Government work · Open Targets 26.06 — CC0 · mixed register set; per-register licences in docs/specs/corpus-20k-sources.md · openFDA / DailyMed — US Government work
✗ required summary fields resolved: 4 required field(s) not terminal: Why people use it, Best-supported result, Biggest unanswered question, Human evidence
✓ public claims reviewed: 0 reviewed claim(s); drafts are never rendered
✓ source coverage passed: 6 source rows
✓ no critical contamination: no quarantine open
✓ canonical metadata passed: slug and display name present
✓ no raw internal fields: enforced by the copy-contract test over the rendered page
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