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Factor Xa Inhibitor Reversal Pregnancy: There are no adequate and well-controlled studies of andexanet alfa in pregnant women to inform patients of associated risks, and animal reproductive and developmental studies have not been conducted. The safety and effectiveness during labour and delivery have not been evaluated.

Andexanet Alfa

Brand names: Ondexxya

Andexanet alfa is a recombinant modified factor Xa decoy protein used as a specific reversal agent for life-threatening or uncontrolled bleeding in patients taking a factor Xa inhibitor such as apixaban or rivaroxaban.

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: Two regimens. LOW DOSE: 400 mg initial intravenous bolus at a target rate of 30 mg/min, followed by a continuous intravenous infusion of 4 mg/min for 120 minutes (480 mg). HIGH DOSE: 800 mg initial intravenous bolus at a target rate of 30 mg/min, followed by a continuous intravenous infusion of 8 mg/min for 120 minutes (960 mg).
Route: For intravenous use only — bolus then continuous infusion, given through a 0.2 or 0.22 micron in-line polyethersulfone or equivalent low protein-binding filter
Frequency: Single treatment course. Start the continuous infusion within two minutes of completing the bolus and run it for 120 minutes. The safety and effectiveness of more than one dose have not been evaluated.
Max: The high-dose regimen (800 mg bolus plus 8 mg/min for 120 minutes, total 960 mg) is the highest regimen described; the safety and efficacy of an additional dose have not been established.
DOSE SELECTION — CRITICAL GAP: the regimen is chosen on the specific FXa inhibitor, the dose of that FXa inhibitor, and the time since the patient's last dose. The dose-selection table (Table 2) was captured INCOMPLETELY in this bundle — the fetched text contains only fragments reading 'FXa Inhibitor Last Dose 10 mg or Unknown: High Dose' and 'Apixaban: 5 mg or less, Low Dose; more than 5 mg or Unknown, High Dose', with the rivaroxaban rows and the entire time-since-last-dose column missing. Do NOT select low versus high dose from this draft — the clinician must read the complete Table 2 in the label. VIALS: low dose = 5 x 200 mg vials (2 for the bolus, 3 for the infusion); high dose = 9 x 200 mg vials (4 for the bolus, 5 for the infusion). Reconstituted concentration is 10 mg/mL (200 mg vial reconstituted with 20 mL Sterile Water for Injection); reconstituted product is stable at room temperature for up to eight hours, or up to 24 hours at 2 to 8 degrees C in vials. RESTARTING ANTICOAGULATION: reversing FXa inhibitor therapy exposes patients to the thrombotic risk of their underlying disease — resume anticoagulant therapy as soon as medically appropriate. PAEDIATRIC: safety and efficacy in the paediatric population have not been studied. SOURCE: no UK SPC was fetched in this bundle — this draft is distilled from the US ANDEXXA prescribing information and must be verified against the UK SPC (the UK product and its dosing tables may differ).

Dose auto-extracted from 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

  • None stated — the US label section 4 Contraindications reads 'None'

Side effects

  • Urinary tract infection — most common (at least 5%) in bleeding patients
  • Pneumonia — most common (at least 5%) in bleeding patients
  • Arterial and venous thromboembolic events, ischaemic events and cardiac events including sudden death — a thrombotic event occurred in 45 of 419 patients (10.7%) in ANNEXA-4, median time to first event 10 days
  • Unresponsiveness to unfractionated heparin following administration
  • Re-elevation or incomplete reversal of anticoagulant activity

Interactions

  • Unfractionated heparin — do not use following andexanet alfa administration; unresponsiveness has occurred, characterised by non-prolongation of activated clotting times and a requirement for increased heparin dosing
  • Anti-FXa activity assays — current commercial clinical assays are unsuitable for measuring FXa activity after andexanet alfa; high sample dilution dissociates the inhibitor and gives erroneously elevated anti-FXa levels, underestimating the reversal effect

Clinical monograph

How it works

It is a catalytically inactive factor Xa analogue that binds and sequesters factor Xa inhibitors, removing their anticoagulant effect and restoring endogenous thrombin generation.

Prescribing in practice

  • Thromboembolic events — including arterial and venous thrombosis, ischaemic stroke and cardiac arrest — have been reported after use, so it must be reserved for serious bleeding and resumption of anticoagulation considered once clinically appropriate.
  • It is given as a bolus followed by a continuous infusion, with the regimen selected according to the specific factor Xa inhibitor, its dose and the time since the last dose.
  • It is not indicated for reversal of direct thrombin inhibitors and has limited supporting data for agents other than apixaban and rivaroxaban.

Monitoring

Monitor for re-bleeding and for clinical signs of thromboembolism after administration, alongside standard haemodynamic observation.

Counselling the patient

  • This is an emergency hospital treatment used to stop serious bleeding.
  • The care team will weigh up the risk of new clots and restart anticoagulation when it is safe.
  • Routine clotting blood tests do not reliably reflect how well it is working.

Evidence & guidelines

Andexanet alfa is the licensed specific reversal agent for factor Xa inhibitors, supported by the ANNEXA-4 study and reviewed by NICE/MHRA.

Reference: ANNEXA-4 Trial (Connolly et al. NEJM 2019); NICE TA697; SPC Ondexxya; 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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