A factor Xa inhibitor reversal agent
Andexanet alfa
An emergency antidote that reverses the blood-thinners apixaban and rivaroxaban in life-threatening bleeding.
What is Andexanet alfa?
Andexanet alfa is a reversal agent for the blood-thinners apixaban and rivaroxaban, which belong to the factor Xa inhibitor group. It is given by injection in hospital when someone on one of these medicines has life-threatening or uncontrolled bleeding. It works as a decoy that mops up the blood thinner so normal clotting can resume. It is a specialist, hospital-only treatment, and because reversing a blood thinner restores the risk of clots, there is a recognised risk of clotting after it is given. Its brand name is Ondexxya.
Education and reference only. This is a plain-language guide to Andexanet alfa — 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
Andexanet alfa is an emergency reversal agent for certain blood thinners, specifically the factor Xa inhibitors apixaban and rivaroxaban. It is a specially made protein that acts as a decoy version of the body's clotting factor Xa. Given by injection into a vein in hospital, it is used when a person taking apixaban or rivaroxaban develops serious or uncontrolled bleeding. It is a specialist medicine given by trained teams and is not used at home.
How it works
Apixaban and rivaroxaban thin the blood by blocking factor Xa, a protein needed to form clots. Andexanet alfa is a modified, inactive copy of factor Xa that acts as a decoy: the blood thinner binds to it instead of to the body's real factor Xa. With the medicine soaked up, the person's own factor Xa is freed to work again and clotting can resume. The effect helps control bleeding, but it also means the person is no longer protected against clots.
Company & origin
Originated / developed by: Alexion / AstraZeneca.
A specialist reversal medicine used in UK hospitals to counter the blood-thinners apixaban and rivaroxaban in serious bleeding.
Practical use
How to take Andexanet alfa
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- It is given as an injection followed by an infusion into a vein by trained staff in hospital.
- It is used only in emergencies, for serious or uncontrolled bleeding while you are taking apixaban or rivaroxaban.
- Tell the team exactly which blood thinner you take and when you last took it, as this guides the right reversal.
- You will be monitored closely afterwards for any signs of a clot, as the risk of clotting returns.
- Your team will discuss when it is safe to restart a blood thinner once the bleeding is controlled.
Weighing it up
Advantages & disadvantages of Andexanet alfa
Advantages
- Reverses the effect of apixaban and rivaroxaban in life-threatening bleeding.
- Acts as a targeted decoy that frees the body's own clotting to resume.
- Provides a specific option for serious bleeding in people on these common blood thinners.
Disadvantages
- Carries a recognised risk of clots, such as heart attack, stroke or clots in the veins and lungs, after reversal.
- Only reverses apixaban and rivaroxaban, not dabigatran or warfarin.
- Is a specialist, hospital-only medicine, and the underlying clot risk returns once it is given.
Practical use
Good to know
Andexanet alfa is a specialist, hospital-only treatment reserved for life-threatening or uncontrolled bleeding in people taking apixaban or rivaroxaban. The most important caution is that reversing a blood thinner brings back the very clot risk the medicine was preventing, and andexanet itself is associated with a risk of clotting events such as heart attack, stroke or clots in the veins and lungs after it is given. Because of this, the team weighs the danger of the bleeding against the clot risk, and plans when it is safe to restart anticoagulation once the emergency has passed. It is used for apixaban and rivaroxaban; it is not the reversal agent for dabigatran, which has its own specific antidote.
Who should not take it / use with caution
- It is not used to reverse blood thinners other than the factor Xa inhibitors apixaban and rivaroxaban.
- Used with great care in people at very high risk of clotting, weighing this against the danger of the bleeding.
- Its use is limited to emergency, hospital settings under specialist supervision.
Monitoring
- Close watching for control of bleeding and the person's overall condition after it is given.
- Careful monitoring for signs of a clot, such as chest pain, breathlessness or limb swelling.
- Reviewing when it is safe to restart a blood thinner, as the underlying clot risk returns.
Side effects
- Clotting events such as heart attack, stroke, or clots in the veins or lungs after reversal.
- Infusion-related reactions such as flushing, feeling hot, or chills.
- The return of the underlying clot risk once the blood thinner is reversed.
Key interactions
- It is intended to reverse apixaban and rivaroxaban and acts on these factor Xa inhibitors.
- It can affect certain clotting tests, so results are interpreted with care by the team.
- Decisions about restarting anticoagulation afterwards are made by the specialist team to balance bleeding and clot risk.
Available as: Powder made into a solution for injection and infusion into a vein, given by healthcare professionals.
Answers
Andexanet alfa: frequently asked questions
What is andexanet alfa used for?
It is an emergency antidote that reverses the blood-thinners apixaban and rivaroxaban, used in hospital for life-threatening or uncontrolled bleeding in people taking these medicines.
How does it work?
It acts as a decoy copy of clotting factor Xa, so the blood thinner binds to it instead of to the body's own factor Xa, allowing normal clotting to resume.
Does it reverse all blood thinners?
No. It reverses apixaban and rivaroxaban, but not dabigatran (which has its own antidote) or warfarin.
Is there a risk after it is given?
Yes. Reversing a blood thinner brings back the risk of clots, and andexanet itself is linked to clotting events such as heart attack or stroke, so you are monitored closely.
Will I restart my blood thinner?
Often yes. The reason you were taking the blood thinner remains, so your team will plan when it is safe to restart anticoagulation after the bleeding is controlled.
Authoritative sources
- BNF
- NICE CKS
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