Indirect Factor Xa Inhibitor — VTE Prophylaxis / Treatment Pregnancy: Use with caution — limited data; crosses placenta minimally; use only if benefit outweighs risk

Fondaparinux

Brand names: Arixtra

Adult dose

Dose: Prophylaxis: 2.5 mg SC once daily; Treatment (DVT/PE): 5 mg (<50 kg), 7.5 mg (50–100 kg), 10 mg (>100 kg)

Route: Subcutaneous injection

Frequency: Once daily

Max: 10 mg/day (treatment)

Prophylaxis: start 6–8 hours post-surgery. Treatment: continue 5–10 days, then switch to oral anticoagulant. No dose adjustment needed for obesity. HIT: safe alternative — does not bind PF4 and is not associated with HIT. No antidote (protamine ineffective); andexanet alfa under investigation.

Paediatric dose

Route:

Seek specialist opinion — not licensed under 17 years

Dose adjustments

Renal

Contraindicated if CrCl <20 mL/min (prophylaxis) or <30 mL/min (treatment) — renally cleared

Hepatic

Use with caution in severe hepatic impairment — coagulopathy risk

Clinical pearls

Fondaparinux is a synthetic pentasaccharide — binds antithrombin and selectively inhibits Xa; unlike heparins, does not bind PF4 so HIT risk is essentially zero
No anti-IIa activity (does not inhibit thrombin directly)
Cannot be reversed with protamine — no licensed antidote available; andexanet alfa may partially reverse but not licensed for fondaparinux
Preferred anticoagulant in HIT patients requiring continued anticoagulation for VTE
Once-daily SC dosing with predictable pharmacokinetics — no routine monitoring required

Contraindications

CrCl <20 mL/min (prophylaxis) / <30 mL/min (treatment)
Active major bleeding
Bacterial endocarditis
Body weight <50 kg for surgical prophylaxis

Side effects

Bleeding (major and minor)
Thrombocytopaenia (rare — unlike heparins, not HIT-mediated)
Elevated LFTs
Injection site reactions
Anaemia

Interactions

Anticoagulants — additive bleeding risk
NSAIDs — increased bleeding risk
Antiplatelets — additive bleeding

Monitoring

Renal function before and during treatment
FBC
Signs of bleeding
Anti-Xa levels not routinely required but available

Reference: BNFc; BNF 90; NICE NG89 (VTE Prevention); MATISSE-DVT/PE Trials; ESC Guidelines 2019 PE. Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways