An injectable anticoagulant
Fondaparinux
An injectable blood thinner given under the skin to treat and prevent blood clots.
What is Fondaparinux?
Fondaparinux is an injectable anticoagulant ('blood thinner') that blocks clotting factor Xa to treat and prevent clots. It is given as a small injection under the skin. It is used around surgery, for certain heart conditions, and to treat clots in the veins.
Education and reference only. This is a plain-language guide to Fondaparinux — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Fondaparinux is a synthetic anticoagulant that works in a similar way to low-molecular-weight heparins. It is supplied as a ready-to-use injection given just under the skin.
How it works
Fondaparinux binds to the natural protein antithrombin and sharply increases its ability to switch off clotting factor Xa. This interrupts the clotting cascade, helping to stop clots forming and growing.
Company & origin
Originated / developed by: Originally developed by Sanofi..
Introduced in the early 2000s as a synthetic factor Xa inhibitor given by injection.
What it treats
Conditions Fondaparinux is used for
Practical use
How to take Fondaparinux
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Given as an injection just under the skin, usually into the fatty fold of the abdomen.
- Rotate injection sites and pinch a skin fold; do not rub afterwards.
- A nurse or pharmacist can show you or a carer how to inject if needed.
- Take it at around the same time each day as prescribed.
- Do not stop early without advice, as clot risk may return.
- Report unusual bruising or bleeding promptly.
Weighing it up
Advantages & disadvantages of Fondaparinux
Advantages
- Predictable effect, usually without routine blood-level testing.
- Fully synthetic and not derived from animal heparin.
- Given once a day, which is convenient for many people.
- An option when heparin has caused problems in the past.
Disadvantages
- Must be injected under the skin rather than taken as a tablet.
- Should be used with caution, or avoided, in significant kidney problems.
- There is no simple antidote to reverse it quickly if bleeding occurs.
- Carries a bleeding risk like all anticoagulants.
Practical use
Good to know
Because it is fully synthetic, it does not contain animal-derived heparin and is sometimes chosen when there has been a problem with heparin in the past. In particular, it is sometimes chosen when heparin has caused a serious drop in platelets (heparin-induced thrombocytopenia, HIT), because it does not usually cause the same reaction. It is given as a quick injection under the skin.
Who should not take it / use with caution
- People with active major bleeding or very high bleeding risk.
- Those with severe kidney problems (seek specialist advice).
- People with certain active infections of the heart valves (endocarditis).
- Anyone allergic to fondaparinux.
- If you are due to have a spinal or epidural injection or a lumbar puncture, tell your team — the timing of these injections must be carefully managed to avoid bleeding around the spine (a rare but serious risk that can affect the nerves).
Monitoring
- Kidney function is checked, as the drug is cleared by the kidneys.
- Watch for any signs of bleeding during treatment.
- Full blood count may be checked during longer courses.
Side effects
- Bleeding or easy bruising.
- Pain, bruising, or redness at the injection site.
- Anaemia (a drop in red blood cells) in some people.
- Rarely, low platelets or changes in liver blood tests.
Key interactions
- Other anticoagulants and antiplatelets (such as aspirin or clopidogrel) increase bleeding risk.
- NSAID painkillers add to bleeding risk.
- Tell your team about all your medicines before starting.
Available as: Pre-filled injection given under the skin.
Answers
Fondaparinux: frequently asked questions
How is fondaparinux different from heparin?
It is fully synthetic and targets clotting factor Xa specifically. It does not contain animal-derived heparin, so it can be an option when heparin has caused problems.
How is it given?
As a small injection just under the skin, usually into the tummy, typically once a day.
Can I use it with kidney problems?
It needs caution and may be avoided if kidney function is significantly reduced, because it is cleared by the kidneys. Your team will check this first.
Is there an antidote?
There is no simple quick reversal agent, so any serious bleeding is managed supportively under specialist care.
When should I get help?
Seek urgent advice for bleeding that will not stop, blood in urine or stool, or heavy unexplained bruising.
The wider class
About Heparins
Fondaparinux belongs to the heparins class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF
- NICE CKS
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