Anticoagulant — Selective Factor Xa Inhibitor (Synthetic Pentasaccharide) Pregnancy: There are no adequate data from use in pregnant women and animal studies are insufficient. Fondaparinux should not be prescribed to pregnant women unless clearly necessary. Breast-feeding is not recommended during treatment, although oral absorption by the child is unlikely.

Fondaparinux (Orthopaedic VTE Prophylaxis)

Brand names: Arixtra

Fondaparinux is a synthetic selective factor Xa inhibitor given subcutaneously for venous thromboembolism prophylaxis after major orthopaedic surgery, including hip fracture, hip and knee replacement.

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: 2.5 mg once daily

Route: Deep subcutaneous injection (patient lying down; alternate between left/right anterolateral and left/right posterolateral abdominal wall). Must NOT be administered intramuscularly.

Frequency: Once daily, administered post-operatively; the initial dose should be given 6 hours following surgical closure, provided that haemostasis has been established

Indication in the fetched SPC: 'Patients undergoing major orthopaedic or abdominal surgery'. Treatment should be continued until the risk of venous thromboembolism has diminished, usually until the patient is ambulant, at least 5 to 9 days after surgery. In patients undergoing hip fracture surgery the risk of VTE continues beyond 9 days, and prolonged prophylaxis with fondaparinux should be considered for up to an additional 24 days. Timing of the first injection requires strict adherence (not earlier than 6 hours following surgical closure, and not unless haemostasis has been established) in patients aged ≥75 years, and/or with body weight <50 kg, and/or with renal impairment with creatinine clearance between 20 and 50 ml/min. Patients with body weight <50 kg are at increased risk of bleeding — elimination decreases with weight, so use with caution. Hepatic impairment: no dose adjustment for mild or moderate impairment; use with care in severe hepatic impairment (not studied). Do not expel the air bubble from the pre-filled syringe before injection. PAEDIATRIC: the SPC states fondaparinux is not recommended for use in children below 17 years of age due to a lack of data on safety and efficacy. Source quote (§4.2): 'The recommended dose of fondaparinux is 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.'

Dose adjustments

Renal

Prophylaxis of VTE: should not be used if creatinine clearance <20 ml/min (contraindicated); the dose should be reduced to 1.5 mg once daily in patients with creatinine clearance 20–50 ml/min; no dosage reduction is required for creatinine clearance >50 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 (including rare intracranial/intracerebral and retroperitoneal bleeding)
Anaemia and post-operative haemorrhage (common)
Haematoma, purpura, epistaxis, gastrointestinal bleeding, haematuria, haemarthrosis, bruising (common)
Nausea and vomiting (common); abdominal pain, dyspepsia, gastritis (uncommon)
Post-operative wound infection (common); headache (common)
Thrombocytopenia, thrombocythaemia, coagulation disorder, hypokalaemia, hypotension, dizziness, confusion (uncommon)

Interactions

For prevention of VTE, agents that may enhance the risk of haemorrhage should not be given concomitantly: desirudin, fibrinolytic agents, GP IIb/IIIa receptor antagonists, heparin, heparinoids or low molecular weight heparin (UK SPC §4.4)
Other antiplatelet agents (acetylsalicylic acid, dipyridamole, sulfinpyrazone, ticlopidine, clopidogrel) and NSAIDs — use with caution; if co-administration is essential, close monitoring is necessary (UK SPC §4.4)
Concomitant vitamin K antagonist therapy, when required, should be given in accordance with UK SPC §4.5
In clinical studies, concomitant warfarin, acetylsalicylic acid, piroxicam and digoxin did not significantly affect the pharmacokinetics/pharmacodynamics of fondaparinux, and fondaparinux is not expected to interact significantly via CYP450 inhibition (US label §7)

Clinical monograph

How it works

It binds antithrombin to selectively and indirectly inhibit factor Xa, interrupting the coagulation cascade without direct activity against thrombin.

Prescribing in practice

Bleeding risk is increased and it is contraindicated in severe renal impairment because of accumulation; the first post-operative dose timing must respect haemostasis and any neuraxial catheter.
Contraindicated in active clinically significant bleeding and bacterial endocarditis.
Unlike heparins it does not usually cause heparin-induced thrombocytopenia, but there is no specific reversal agent in routine use.

Monitoring

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

Counselling the patient

Given as a once-daily injection under the skin after surgery.
Report any unusual or persistent bleeding or bruising.
Take care to give it at the recommended time in relation to your operation.

Evidence & guidelines

NICE NG89 lists fondaparinux among pharmacological options for VTE prophylaxis after major orthopaedic surgery.

Reference: PENTATHLON 2000 Trial (NEJM 2001); NICE NG89; SPC Arixtra; 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