ClinCalc Pro
Menu
Calculators Drugs Pathways AI Dx Donate Get the App
Anticoagulant — Factor Xa Inhibitor (Indirect) Pregnancy: Avoid if possible — limited data; if required for HIT or severe heparin allergy, use under specialist supervision; does not cross placenta significantly

Fondaparinux (Surgical VTE Prophylaxis)

Brand names: Arixtra

Adult dose

Dose: Orthopaedic/abdominal surgery VTE prophylaxis: 2.5 mg SC once daily; start 6–8 hours post-surgery; continue for 5–9 days (abdominal) or 5–35 days (hip/knee replacement)
Route: Subcutaneous injection
Frequency: Once daily
Max: 2.5 mg/day (prophylaxis); 5–10 mg/day (treatment of DVT/PE)
Synthetic pentasaccharide — selectively inhibits factor Xa via antithrombin. No direct thrombin inhibition. Not reversible by protamine. NICE recommends fondaparinux for major orthopaedic surgery VTE prophylaxis (NICE NG89). Do not use within 6 hours post-surgery (bleeding risk).

Paediatric dose

Dose: Not licensed in children under 17 years N/A/kg
Route: N/A
Frequency: N/A
Max: N/A
Not licensed in paediatrics. Off-label use in specialist thrombosis centres only.

Dose adjustments

Renal

Contraindicated if eGFR <20 mL/min. eGFR 20–30 mL/min: use with caution — increased bleeding risk, no dose reduction guidance. eGFR >30 mL/min: standard dose.

Hepatic

No dose adjustment required.

Paediatric weight-based calculator

Not licensed in paediatrics. Off-label use in specialist thrombosis centres only.

Clinical pearls

  • PENTATHLON 2000 trial (NEJM 2001): fondaparinux 2.5 mg significantly reduced VTE after major knee surgery vs enoxaparin; EPHESUS trial (NEJM 2001): superiority in hip fracture surgery — fondaparinux became the benchmark for orthopaedic VTE prophylaxis
  • HIT advantage: fondaparinux does not cause HIT (cannot form PF4-fondaparinux antibody complex) — can be used as VTE prophylaxis in patients with prior HIT or strong HIT suspicion
  • No antidote: fondaparinux has no licensed reversal agent — protamine has no effect. In bleeding: supportive care, rFVIIa (off-label, last resort), or andexanet alfa (licensed for direct Xa inhibitors — off-label for fondaparinux)
  • First dose timing: critically important — NICE NG89 specifies 6–8 hours post-surgery; giving earlier significantly increases bleeding complications

Contraindications

  • eGFR <20 mL/min
  • Active major bleeding
  • Bacterial endocarditis
  • Body weight <50 kg (prophylaxis dose — higher bleeding risk)

Side effects

  • Bleeding (major and minor surgical site bleeding)
  • Thrombocytopenia (HIT type: rare — fondaparinux does not bind PF4 and very rarely causes HIT; can be used as HIT alternative)
  • Anaemia
  • Injection site bruising

Interactions

  • NSAIDs and antiplatelet agents (additive bleeding risk)
  • Direct oral anticoagulants (avoid overlap — increased bleeding)
  • Thrombolytics (increased haemorrhagic risk)

Monitoring

  • Anti-Xa levels (if renal impairment or body weight extremes)
  • Platelet count (baseline and day 5–8)
  • Renal function before starting
  • Signs of bleeding (wound, GI, neurological)

Reference: BNFc; BNF 90; NICE NG89 (VTE Prophylaxis); PENTATHLON 2000 Trial (NEJM 2001); MHRA SPC Arixtra; ESC VTE Guidelines 2019. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

Calculators
Pathways