Fondaparinux
Arixtra
Synthetic indirect factor Xa inhibitor (pentasaccharide)
Binds antithrombin → selective, exclusive factor Xa inhibition (no IIa activity). Does NOT cause HIT — safe alternative in HIT patients.
Indications
- •VTE prophylaxis + treatment
- •HIT (off-label alternative anticoagulant)
Dosing
| Context | Adult | Pediatric |
|---|---|---|
| Prophylaxis | 2.5 mg SC daily | — |
| Treatment | 5–10 mg SC daily (weight-based: <50 kg =5, 50–100=7.5, >100=10) | — |
Pharmacokinetics
Onset ~2 h. Long half-life 17–21 h → once-daily. Renally cleared — contraindicated CrCl <30.
Side effects
- !Bleeding
- !No HIT
- !Accumulation in renal failure
Contraindications
- ×CrCl <30
- ×Body weight <50 kg (prophylaxis)
- ×Active bleeding
Reversal / antidote
No specific reversal; protamine INEFFECTIVE. Consider rFVIIa for life-threatening bleed.
Clinical pearls
- ★ASRA neuraxial: avoid if possible; if used, single atraumatic needle pass, no indwelling catheter, and 36–42 h hold — the strictest guidance among the parenterals.
- ★Does not cause HIT — useful when HIT suspected but a parenteral agent is needed.
- ★No effective reversal + long half-life = respect it in bleeding patients.
Other drugs in Coagulation Related
- Heparin (unfractionated)
Activates antithrombin → inactivates IIa (thrombin) and Xa.
- Tranexamic Acid (TXA)
Reversibly binds plasminogen, blocking conversion to plasmin → preserves fibrin clot.
- Protamine Sulfate
Strongly basic (positive-charge) protein binds to highly acidic (negative-charge) heparin → inactive ionic complex → renal excretion. 1 mg protamine neutralizes ~100 units heparin.
- DDAVP (Desmopressin)
Selective V2 agonist (renal water retention + Factor VIII/vWF release from endothelial Weibel-Palade bodies). NO V1 vasopressor activity at therapeutic dose.
- Warfarin
Inhibits vitamin K epoxide reductase (VKORC1) → depletes reduced vitamin K → ↓ synthesis of factors II, VII, IX, X and proteins C/S. Full effect takes days (waits for existing factor decay).
- Enoxaparin
Antithrombin-mediated inhibition, weighted toward factor Xa over IIa (~3.8:1). More predictable than UFH — no routine monitoring.
- Dalteparin
Antithrombin-mediated factor Xa > IIa inhibition. Similar profile to enoxaparin; preferred LMWH in cancer-associated VTE (CLOT trial).
- Tinzaparin
Antithrombin-mediated factor Xa > IIa inhibition; higher mean molecular weight than enoxaparin (anti-Xa:IIa ~1.9:1).
Browse all classes: /reference/drugs
Suggested reading
- •Miller's Anesthesia, 9e
- •FDA package insert
- •ASRA regional anesthesia in the anticoagulated patient guidelines, 2018
