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Synthetic factor Xa inhibitor Pregnancy: UK SPC §4.6, verbatim — Pregnancy: 'No clinical data on exposed pregnancies are available. Animal studies are insufficient with respect to effects on pregnancy, embryo/foetal development, parturition and postnatal development because of limited exposure. Fondaparinux should not be prescribed to pregnant women unless clearly necessary.' Breast-feeding: 'Fondaparinux is excreted in rat milk but it is not known whether fondaparinux is excreted in human milk. Breast-feeding is not recommended during treatment with fondaparinux. Oral absorption by the child is however unlikely.' Fertility: 'There are no data available on the effect of fondaparinux on human fertility. Animal studies do not show any effect on fertility.' US label §8.1 is less restrictive: 'Available data from published literature and postmarketing reports have not reported a clear association with fondaparinux sodium and adverse developmental outcomes. Fondaparinux sodium plasma concentrations obtained from four women treated with fondaparinux sodium injection during pregnancy and their newborn infants demonstrated low placental transfer of fondaparinux sodium... There are risks to the mother associated with untreated venous thromboembolism in pregnancy and a risk of haemorrhage in the mother and fetus associated with use of anticoagulants.' For UK practice follow the SPC wording.

Fondaparinux sodium

Brand names: Arixtra

Fondaparinux sodium is a synthetic selective factor Xa inhibitor given by subcutaneous injection for the prevention and treatment of venous thromboembolism and in certain acute coronary syndromes.

Adult dose

Dose: VTE TREATMENT (acute DVT / PE) — UK SPC: 7.5 mg once daily by subcutaneous injection in patients with body weight ≥ 50 kg and ≤ 100 kg; 5 mg once daily if body weight is < 50 kg; 10 mg once daily if body weight is > 100 kg. Continue for at least 5 days and until adequate oral anticoagulation is established (INR 2 to 3), starting the oral anticoagulant as soon as possible and usually within 72 hours. VTE PROPHYLAXIS after hip fracture, hip replacement, knee replacement or abdominal surgery — US labelling only, because no UK prophylaxis licence is in this bundle: 2.5 mg subcutaneously once daily, the initial dose given no earlier than 6 to 8 hours after surgery and after haemostasis has been established, usual duration 5 to 9 days, with up to 24 additional days of extended prophylaxis after hip fracture surgery.
Route: Deep subcutaneous injection only. UK SPC §4.4: 'Fondaparinux is intended for subcutaneous use only. Do not administer intramuscularly.' §4.2: 'Fondaparinux is administered by deep subcutaneous injection while the patient is lying down. Sites of administration should alternate between the left and the right anterolateral and left and right posterolateral abdominal wall. To avoid the loss of medicinal product when using the pre-filled syringe do not expel the air bubble from the syringe before the injection. The whole length of the needle should be inserted perpendicularly into a skin fold held between the thumb and the forefinger; the skin fold should be held throughout the injection.'
Frequency: Once daily
SCOPE: this page lists VTE prophylaxis, VTE treatment AND unstable angina/NSTEMI. Two of the three are published above — the weight-banded VTE TREATMENT regimen from the UK SPC (the primary, UK-licensed figure) and the 2.5 mg surgical VTE PROPHYLAXIS regimen from the US label, explicitly marked as US labelling because no UK prophylaxis licence was fetched. THE UA/NSTEMI (AND STEMI) INDICATION IS NOT DOSED HERE: the acute coronary syndrome licence belongs to the 2.5 mg fondaparinux SPC, which is not in this bundle, and the US label in this bundle has no ACS indication at all. The UK SPC fetched here mentions ACS only in §4.8 as safety-database context ('10,057 patients undergoing treatment of UA or NSTEMI ACS (Arixtra 2.5 mg/0.5 ml)', '6,036 patients undergoing treatment of STEMI ACS'), which is not a posology statement. Fetch the 2.5 mg SPC before publishing any ACS dose on this page. DOSE VERBATIM (UK SPC §4.2): 'The recommended dose of fondaparinux is 7.5 mg (patients with body weight ≥ 50, ≤ 100kg) once daily administered by subcutaneous injection. For patients with body weight < 50 kg, the recommended dose is 5 mg. For patients with body weight > 100 kg, the recommended dose is 10 mg. Treatment should be continued for at least 5 days and until adequate oral anticoagulation is established (International Normalised Ratio 2 to 3). Concomitant oral anticoagulation treatment should be initiated as soon as possible and usually within 72 hours. The average duration of administration in clinical trials was 7 days and the clinical experience from treatment beyond 10 days is limited.' PROPHYLAXIS VERBATIM (US label §2.2 / §2.3, NOT UK): 'In patients undergoing hip fracture, hip replacement, or knee replacement surgery, the recommended dose of fondaparinux sodium injection is 2.5 mg administered by subcutaneous injection once daily after hemostasis has been established. Administer the initial dose no earlier than 6 to 8 hours after surgery. Administration of fondaparinux sodium injection earlier than 6 hours after surgery increases the risk of major bleeding. The usual duration of therapy is 5 to 9 days... In patients undergoing hip fracture surgery, an extended prophylaxis course of up to 24 additional days is recommended.' The abdominal-surgery dose in §2.3 is the same 2.5 mg once daily. NO MAXIMUM IS PUBLISHED: neither label states a maximum dose for fondaparinux. The 10 mg figure is the recommended dose for one weight band, not a ceiling, so maxDose is left empty rather than presenting 10 mg as a cap. ELDERLY (UK SPC §4.2): 'No dosing adjustment is necessary. In patients ≥75 years, fondaparinux should be used with care, as renal function decreases with age (see section 4.4).' LOW BODY WEIGHT (§4.4): 'Clinical experience is limited in patients with body weight <50 kg. Fondaparinux should be used with caution at a daily dose of 5 mg in this population.' RECENT SURGERY (§4.4): 'fondaparinux should be used with caution in patients who have undergone recent surgery (<3 days) and only once surgical haemostasis has been established.' DO NOT CO-ADMINISTER (§4.4): 'Agents that may enhance the risk of haemorrhage should not be administered concomitantly with fondaparinux. These agents include desirudin, fibrinolytic agents, GP IIb/IIIa receptor antagonists, heparin, heparinoids, or Low Molecular Weight Heparin (LMWH).' NEURAXIAL BLOCK (§4.4): 'In patients receiving fondaparinux for treatment of VTE rather than prophylaxis, spinal/epidural anaesthesia in case of surgical procedures should not be used.' UNSUPPORTED PAGE CLAIMS — nothing in this bundle says fondaparinux does not cause or does not cross-react in heparin-induced thrombocytopenia; on the contrary the US label §4 contraindicates it in 'Thrombocytopenia associated with a positive in vitro test for anti-platelet antibody in the presence of fondaparinux sodium', and §5.5 requires discontinuation below 100,000/mm3 platelets. Re-source or remove them; do not treat their absence here as verification. TRUNCATION: eMC §4.4 and §4.8, and US §2, §5, §6, §8.1 and §8.5, are all cut off at the source-fetch limit, so none of these lists is complete.

Paediatric dose

NO PAEDIATRIC DOSE. UK SPC §4.2, verbatim: 'Paediatric population - Fondaparinux is not recommended for use in children below 17 years of age due to limited data on safety and efficacy (see sections 5.1 and 5.2).' US label §8.4: 'Safety and effectiveness of fondaparinux sodium in pediatric patients have not been established. Because risk for bleeding during treatment with fondaparinux sodium is increased in adults who weigh <50 kg, bleeding may be a particular safety concern for use of fondaparinux sodium in the pediatric population.' dosePerKg is null and no weight-based calculation should be offered. If a child or adolescent needs anticoagulation, verify the agent and the dose against a children's formulary and take specialist haematology advice.

Dose adjustments

Renal

UK SPC §4.2, verbatim: 'Fondaparinux should be used with caution in patients with moderate renal impairment (see section 4.4). There is no experience in the subgroup of patients with both high body weight (>100 kg) and moderate renal impairment (creatinine clearance 30-50 ml/min). In this subgroup, after an initial 10 mg daily dose, a reduction of the daily dose to 7.5 mg may be considered, based on pharmacokinetic modelling (see section 4.4). Fondaparinux should not be used in patients with severe renal impairment (creatinine clearance < 30 ml/min) (See section 4.3).' §4.4 adds: 'The risk of bleeding increases with increasing renal impairment. Fondaparinux is known to be excreted mainly by the kidney.' US label §4 contraindicates 'Severe renal impairment (creatinine clearance [CrCl] <30 mL/min).' NO dose reduction other than the 10 mg → 7.5 mg high-body-weight/moderate-impairment consideration is given for the treatment indication in this bundle.

Hepatic

UK SPC §4.2, verbatim: 'No dosing adjustment is necessary in patients with either mild or moderate hepatic impairment. In patients with severe hepatic impairment, fondaparinux should be used with care as this patient group has not been studied (see sections 4.4 and 5.2).' US label §2.5 agrees: 'No dose adjustment is recommended in patients with mild to moderate hepatic impairment, based upon single-dose pharmacokinetic data. Pharmacokinetic data are not available for patients with severe hepatic impairment. Patients with hepatic impairment may be particularly vulnerable to bleeding during fondaparinux sodium therapy. Observe these patients closely for signs and symptoms of bleeding.'

Dose independently re-sourced from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • Hypersensitivity to the active substance or to any of the excipients listed in section 6.1 (UK SPC §4.3)
  • Active clinically significant bleeding (UK SPC §4.3)
  • Acute bacterial endocarditis (UK SPC §4.3)
  • Severe renal impairment defined by creatinine clearance < 30 ml/min (UK SPC §4.3). NOTE: this threshold belongs to the TREATMENT-strength licence fetched here. The UK 2.5 mg prophylaxis licence, which is not in this bundle, uses a different (lower) threshold, so do not apply < 30 ml/min to prophylaxis from this source.
  • US label §4 only: 'Thrombocytopenia associated with a positive in vitro test for anti-platelet antibody in the presence of fondaparinux sodium.'
  • US label §4 only: 'Body weight <50 kg (venous thromboembolism [VTE] prophylaxis only).' The UK treatment SPC does not contraindicate low body weight — §4.4 instead advises caution: 'Clinical experience is limited in patients with body weight <50 kg. Fondaparinux should be used with caution at a daily dose of 5 mg in this population.'
  • US label §4 only: 'History of serious hypersensitivity reaction (e.g., angioedema, anaphylactoid/anaphylactic reactions) to fondaparinux sodium.'

Side effects

  • Bleeding is the principal risk — UK SPC §4.8: 'The most commonly reported serious adverse reactions reported with fondaparinux are bleeding complications (various sites including rare cases of intracranial/ intracerebral and retroperitoneal bleedings).'
  • Common (≥ 1/100, <1/10), blood and lymphatic system: anaemia, post-operative haemorrhage
  • Uncommon (≥ 1/1,000, <1/100), bleeding at other sites: utero-vaginal haemorrhage, haemoptysis, haematuria, haematoma, gingival bleeding, purpura, epistaxis, gastrointestinal bleeding, haemarthrosis, ocular bleeding, bruise
  • Uncommon, platelet and coagulation: thrombocytopenia, thrombocythaemia, platelet abnormal, coagulation disorder
  • Rare (≥ 1/10,000, <1/1,000): retroperitoneal bleeding, hepatic bleeding, intracranial/intracerebral bleeding
  • Immune system: allergic reaction, including very rare reports of angioedema and anaphylactoid/anaphylactic reaction
  • Metabolism: hypokalaemia; non-protein-nitrogen (Npn) increased
  • Nervous system — common: headache; uncommon: anxiety, confusion, dizziness, somnolence, vertigo
  • Vascular: hypotension. Respiratory: dyspnoea (common), coughing (uncommon)
  • Gastrointestinal — common: nausea, vomiting; uncommon: abdominal pain, dyspepsia, gastritis, constipation, diarrhoea
  • Hepatobiliary: abnormal liver function tests, hepatic enzymes increased; bilirubinaemia
  • Skin: rash erythematous, pruritus
  • US label §5.1: 'Spinal or epidural hematomas, which may result in long-term or permanent paralysis, can occur.'
  • The UK §4.8 table is cut off at the source-fetch limit part-way through 'Skin and subcutaneous tissue disorders' / 'General ...' — the list above is not the complete adverse-reaction table.

Monitoring

  • Platelet count — US label §5.5: 'Thrombocytopenia can occur with the administration of fondaparinux sodium. Thrombocytopenia of any degree should be monitored closely. Discontinue fondaparinux sodium if the platelet count falls below 100,000/mm3.'
  • Renal function before and during treatment — US label §8.5: 'Fondaparinux sodium is substantially excreted by the kidney, and the risk of adverse reactions to fondaparinux sodium may be greater in patients with impaired renal function. Because elderly patients are more likely to have decreased renal function, assess renal function prior to fondaparinux sodium administration.'
  • Signs and symptoms of bleeding, with particular vigilance in the elderly — UK SPC §4.4: 'Incidences of bleeding events in patients receiving the recommended regimen in the treatment of DVT or PE and aged <65 years, 65-75 and >75 years were 3.0 %, 4.5 % and 6.5 %, respectively.'
  • Close monitoring if co-administration with antiplatelet agents or NSAIDs is unavoidable — UK SPC §4.4: 'Other antiplatelet medicinal products (acetylsalicylic acid, dipyridamole, sulfinpyrazone, ticlopidine or clopidogrel), and NSAIDs should be used with caution. If co-administration is essential, close monitoring is necessary.'
  • Neurological observation where neuraxial anaesthesia or puncture is involved — UK SPC §4.4: 'In patients receiving fondaparinux for treatment of VTE rather than prophylaxis, spinal/epidural anaesthesia in case of surgical procedures should not be used.'
  • No routine coagulation or anti-Xa monitoring requirement appears in any fetched section of either label (the page's 'anti-Xa levels ... available' line is not supported by this bundle).

Clinical monograph

How it works

It binds antithrombin and accelerates antithrombin-mediated inhibition of factor Xa, interrupting the coagulation cascade without directly inhibiting thrombin.

Prescribing in practice

  • It is largely renally cleared and accumulates in renal impairment, substantially increasing bleeding risk, so it is contraindicated or requires dose reduction depending on renal function and indication.
  • Bleeding is the principal hazard and there is no specific reversal agent, so it should be used cautiously around surgery and neuraxial procedures because of spinal or epidural haematoma risk.
  • Unlike heparin it does not usually cross-react in heparin-induced thrombocytopenia, but routine anti-Xa monitoring is not required.

Monitoring

Assess renal function and platelet count and watch for signs of bleeding rather than relying on routine coagulation monitoring.

Counselling the patient

  • This is a blood-thinning injection given under the skin.
  • Report unusual bruising, bleeding, black stools or blood in urine.
  • Tell any clinician planning surgery or a spinal procedure that you are using it.

Evidence & guidelines

Fondaparinux is supported by landmark venous thromboembolism prophylaxis and treatment trials and is recommended in NICE acute coronary syndrome and VTE guidance.

Reference: NICE NG89/NG185; ESC ACS guidelines; 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).

Related

Curated clinical cross-links plus same-class fallbacks.

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