Anticoagulant — Factor Xa Inhibitor (Indirect) Pregnancy: There are no adequate data from the use of fondaparinux in pregnant women and animal studies are insufficient. 'Fondaparinux should not be prescribed to pregnant women unless clearly necessary.' It is excreted in rat milk; it is not known whether it is excreted in human milk. Breastfeeding is not recommended during treatment, although oral absorption by the child is unlikely.

Fondaparinux (Surgical VTE Prophylaxis)

Brand names: Arixtra

Fondaparinux is a synthetic selective factor Xa inhibitor used for venous thromboembolism prophylaxis after major orthopaedic and other surgery, given by subcutaneous injection.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Patients undergoing major orthopaedic or abdominal surgery: 2.5 mg once daily administered post-operatively by subcutaneous injection. 'The initial dose should be given 6 hours following surgical closure provided that haemostasis has been established. Treatment should be continued until the risk of venous thrombo-embolism has diminished, usually until the patient is ambulant, at least 5 to 9 days after surgery.' In hip fracture surgery the risk of VTE continues beyond 9 days, and prolonged prophylaxis should be considered for up to an additional 24 days.

Route: Deep subcutaneous injection with the patient lying down, alternating sites between the left and right anterolateral and left and right posterolateral abdominal wall; insert the whole length of the needle perpendicularly into a skin fold held throughout the injection, and do not expel the air bubble from the pre-filled syringe. Must not be administered intramuscularly. (Intravenous administration applies only to the first dose in STEMI — through an existing line directly or in a 25 or 50 ml 0.9% saline minibag over 1 to 2 minutes, flushing the tubing afterwards.)

Frequency: Once daily.

Source product is Fondaparinux sodium 2.5 mg/0.5 ml solution for injection in pre-filled syringe. TIMING IN HIGHER-RISK SURGICAL PATIENTS (verbatim): 'In patients undergoing surgery, timing of the first fondaparinux injection requires strict adherence in patients >=75 years, and/or with body weight <50 kg and/or with renal impairment with creatinine clearance ranging between 20 to 50 ml/min. The first fondaparinux administration should be given not earlier than 6 hours following surgical closure. The injection should not be given unless haemostasis has been established.' OTHER INDICATIONS AT THE SAME 2.5 mg STRENGTH — Medical patients at high risk of thromboembolic complications: 2.5 mg once daily subcutaneously; a treatment duration of 6-14 days has been clinically studied. UA/NSTEMI: 2.5 mg once daily subcutaneously, started as soon as possible after diagnosis, for up to a maximum of 8 days or until hospital discharge if earlier; if PCI is undertaken, unfractionated heparin should be given during PCI per standard practice, and in the pivotal trial subcutaneous fondaparinux was restarted no earlier than 2 hours after sheath removal. STEMI: 2.5 mg once daily, first dose intravenously and subsequent doses subcutaneously, for up to a maximum of 8 days or until discharge; in the pivotal trial fondaparinux was restarted no earlier than 3 hours after sheath removal. CABG: 'In STEMI or UA/NSTEMI patients who are to undergo coronary artery bypass graft (CABG) surgery, fondaparinux where possible, should not be given during the 24 hours before surgery and may be restarted 48 hours post-operatively.' Superficial-vein thrombosis: 2.5 mg once daily subcutaneously for a minimum of 30 days and up to a maximum of 45 days in patients at high risk; if such patients are to undergo surgery or other invasive procedures, fondaparinux should where possible not be given during the 24 hours before surgery and may be restarted at least 6 hours post-operatively provided haemostasis has been achieved. LOW BODY WEIGHT: patients under 50 kg are at increased risk of bleeding (elimination decreases with weight) and fondaparinux should be used with caution; for superficial-vein thrombosis it is not recommended in this group. HEPATIC IMPAIRMENT: no dose adjustment in mild or moderate impairment; use with care in severe hepatic impairment (not studied), and not recommended in severe impairment for superficial-vein thrombosis. PCI: use of fondaparinux prior to and during primary PCI in STEMI, or in UA/NSTEMI patients requiring urgent revascularisation, is not recommended; it should not be the sole anticoagulant during non-primary PCI because of the risk of guiding catheter thrombus. PAEDIATRIC (verbatim): 'Fondaparinux is not recommended for use in children below 17 years of age due to a lack of data on safety and efficacy.' No paediatric dose is stated; verify against a children's formulary.

Dose adjustments

Renal

Prophylaxis of VTE: must not be used if creatinine clearance <20 ml/min (contraindicated); reduce the dose to 1.5 mg once daily if creatinine clearance is 20 to 50 ml/min; no reduction is required if creatinine clearance >50 ml/min. Treatment of UA/NSTEMI and STEMI: must not be used if creatinine clearance <20 ml/min; no dose reduction required above 20 ml/min. Treatment of superficial-vein thrombosis: must not be used if creatinine clearance <20 ml/min; reduce to 1.5 mg once daily if creatinine clearance is 20 to 50 ml/min ('The safety and efficacy of 1.5 mg has not been studied'). Note the US label instead contraindicates fondaparinux at creatinine clearance <30 mL/min.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to the active substance or to any of the excipients
Active clinically significant bleeding
Acute bacterial endocarditis
Severe renal impairment defined by creatinine clearance < 20 ml/min

Side effects

Bleeding complications at various sites — the most commonly reported serious adverse reactions; include post-operative haemorrhage, haematoma, purpura, epistaxis, gastrointestinal bleeding, haematuria, gingival bleeding, haemoptysis, bruising
Anaemia (common); rare: retroperitoneal, hepatic and intracranial/intracerebral bleeding
Uncommon: thrombocytopenia, thrombocythaemia, abnormal platelets, coagulation disorder
Common: nausea, vomiting; headache; post-operative wound infections
Uncommon: hypotension, dyspnoea, dizziness, confusion, somnolence, anxiety, vertigo; hypokalaemia
Allergic reaction, including very rare reports of angioedema and anaphylactoid/anaphylactic reaction

Interactions

(eMC §4.5 was not retrieved in this bundle — the following are from eMC §4.4)
For prevention of VTE, agents that may enhance the risk of haemorrhage should not be administered concomitantly: desirudin, fibrinolytic agents, GP IIb/IIIa receptor antagonists, heparin, heparinoids or low molecular weight heparin
Vitamin K antagonists — when required, concomitant therapy should be administered in accordance with §4.5
Other antiplatelet medicinal products (acetylsalicylic acid, dipyridamole, sulfinpyrazone, ticlopidine, clopidogrel) and NSAIDs — use with caution; if co-administration is essential, close monitoring is necessary
In treatment of UA/NSTEMI and STEMI, use with caution with other agents that increase bleeding risk (e.g. GP IIb/IIIa inhibitors or thrombolytics)
US labelling adds that concomitant warfarin, acetylsalicylic acid, piroxicam and digoxin did not significantly affect fondaparinux pharmacokinetics/pharmacodynamics

Clinical monograph

How it works

It binds antithrombin to selectively and indirectly inhibit factor Xa, interrupting the coagulation cascade without directly inhibiting thrombin.

Prescribing in practice

Bleeding is the principal risk and it is renally cleared with a long half-life and no specific reversal agent, so avoid in severe renal impairment and observe strict timing around neuraxial anaesthesia to reduce spinal haematoma risk.
The first postoperative dose timing matters because giving it too early increases surgical bleeding.
It is contraindicated in active major bleeding and in bacterial endocarditis; use caution in low body weight, where bleeding risk is increased.

Monitoring

Monitor renal function and for clinical signs of bleeding; routine coagulation monitoring is not required.

Counselling the patient

Report any unusual bleeding or bruising.
Tell the team about any planned spinal or epidural procedure.

Evidence & guidelines

Its use in surgical VTE prophylaxis is supported by NICE NG89 and pivotal orthopaedic surgery trials.

Reference: NICE NG89 (VTE Prophylaxis); PENTATHLON 2000 Trial (NEJM 2001); MHRA SPC Arixtra; ESC VTE Guidelines 2019; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways