Fondaparinux
2.5 mg SC daily in NSTEMI/unstable angina when angiography is not immediate.
On this page
Dose
| Indication | Dose |
|---|---|
| NSTEMI/unstable angina | 2.5 mg SC once daily (up to 8 days or until discharge) |
| VTE prophylaxis | 2.5 mg SC once daily |
| VTE treatment | Under 50 kg 5 mg, 50–100 kg 7.5 mg, over 100 kg 10 mg SC once daily |
How it works
Fondaparinux is a synthetic pentasaccharide: the small sugar sequence in heparin that binds antithrombin. When bound, antithrombin inhibits factor Xa about 300 times faster, so less thrombin is made and clots stop growing. Unlike heparin, it has no direct effect on thrombin and hardly binds platelet factor 4, so heparin-induced thrombocytopenia (HIT) is very rare. Its long half-life (about 17 to 21 hours) allows once-daily dosing, but it is cleared by the kidneys and there is no specific reversal agent.
When it is used
- NSTEMI and unstable angina, as the anticoagulant of choice in many guidelines when angiography is not planned within 24 hours, given with dual antiplatelet therapy.
- VTE prophylaxis in medical and surgical patients, especially orthopaedic surgery.
- Treatment of DVT and PE, as an alternative to low molecular weight heparin, usually overlapping with warfarin or switching to a DOAC.
- A useful option in patients with a history of HIT (specialist advice).
It is not:
- The sole anticoagulant during PCI: catheter thrombosis occurs, so a bolus of unfractionated heparin is added in the cath lab.
- Recommended for STEMI treated with primary PCI.
- For patients with severe kidney impairment or high bleeding risk.
Cautions
- Avoid if creatinine clearance below 20 (below 30 for treatment doses).
- Bleeding.
Contraindications
- Active major bleeding, or a bleeding disorder.
- Acute bacterial endocarditis.
- Creatinine clearance below the limits above (use the kidney function calculator, which uses Cockcroft-Gault).
- Known allergy to fondaparinux.
Side effects
- Bleeding: injection-site bruising, GI, urinary and, rarely, intracranial bleeding. Spinal or epidural haematoma after neuraxial anaesthesia.
- Anaemia, low platelets (not HIT-related, but still check), raised liver enzymes, rash.
Interactions
Aspirin, clopidogrel, ticagrelor, NSAIDs, other anticoagulants and SSRIs all add to bleeding risk. Stop other anticoagulants before starting it, except during planned overlap with warfarin.
Monitoring
- Before starting: FBC (platelets, Hb), creatinine and eGFR, clotting screen, weight.
- During treatment: FBC and creatinine every few days in hospital, and if bleeding is suspected.
- Routine anti-Xa level monitoring is not needed. Normal clotting tests (APTT, INR) are not affected in a useful way.
- Watch for black stools, haematuria and haematoma, especially in older patients on dual antiplatelets.
Pregnancy and breastfeeding
Low molecular weight heparin is the anticoagulant of choice in pregnancy. Fondaparinux may be used on specialist advice, for example in women with heparin allergy or HIT. Small amounts may pass into breast milk; LMWH is preferred.
Practical tips
- Comes as pre-filled syringes. Inject deep SC into the abdominal wall, alternating sides; do not expel the air bubble.
- In NSTEMI, give the first dose as soon as the diagnosis is made, alongside aspirin and a P2Y12 inhibitor.
- For prophylaxis after surgery, the first dose is usually given at least 6 hours after the operation once bleeding is controlled.
- Spinal or epidural procedures need careful timing; follow your anaesthetic team's guidance.
- Check the indication on the drug chart; treatment and prophylaxis doses are very different.
If a patient on fondaparinux needs an urgent procedure or starts bleeding, there is no specific antidote. Stop it, get senior help and use supportive measures; the drug lasts about a day.
See Acute coronary syndrome, Calf pain and DVT and Pulmonary embolism. For exam pharmacology, read Anticoagulants and antiplatelets.
Frequently asked questions
Why is fondaparinux used in NSTEMI?
It reduces bleeding compared with enoxaparin while preventing ischaemic events (NICE).
Can fondaparinux be reversed?
There is no specific reversal agent. Protamine does not work. Because its effect lasts about a day, bleeding is managed by stopping the drug and supportive treatment, with specialist advice.
Does fondaparinux cause HIT?
Very rarely. It is so small that it does not form the antibody complexes that cause heparin-induced thrombocytopenia, which is why it is used in some patients with a history of HIT.
Can fondaparinux be used in kidney failure?
No. It is cleared by the kidneys and builds up. Avoid it below a creatinine clearance of 20 mL/min (30 for treatment doses).
Used in these guides
Sources
Doses on this page are typical doses from the sources above. Always confirm with a current drug reference, the product leaflet and your hospital protocol, especially in children, pregnancy and kidney or liver disease.
For FCPS Part 1
Revising for FCPS Part 1? Fondaparinux is covered in our textbook chapter Anticoagulants and antiplatelets, with practice MCQs.