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Educational draft · awaiting clinical reviewUse Rapid for revision, not patient-care decisions. Check current national and local guidance and the BNF or BNFC before acting.

Warfarin monitoring and reversal

Haematology and transfusion · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

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Major warfarin-associated haemorrhage

Intracranial, retroperitoneal, pericardial, airway or ongoing haemodynamic bleeding requires immediate reversal even before the laboratory INR returns when warfarin exposure is known.

Action: Stop warfarin, resuscitate and control the source, send urgent INR, FBC, fibrinogen, renal, liver and group samples, give four-factor prothrombin complex concentrate with 5–10 mg slow intravenous phytomenadione under the major-haemorrhage protocol and recheck clinical haemostasis and INR.

Synopsis

Start and monitor warfarin safely, interpret INR in clinical context, manage interruptions and reverse excessive anticoagulation according to bleeding severity and urgency.

  • Warfarin inhibits vitamin-K recycling and lowers functional factors II, VII, IX and X; the delayed fall and recovery mean INR changes lag behind dose changes.
  • Use an indication-specific target, commonly target INR 2.5 with range 2.0–3.0 for VTE and AF; mechanical valve targets depend on valve type, position and additional embolic risks.
  • Monitor INR more frequently during initiation and after illness, interacting medicine, diet or alcohol change, missed doses or unstable control; stable patients can move to longer locally defined intervals.
  • Major bleeding: stop warfarin and give four-factor PCC plus 5–10 mg slow IV phytomenadione; vitamin K alone is too slow and plasma is not routine first-line replacement when PCC is available.
  • No bleeding with INR above 8: omit warfarin and give 1–5 mg oral phytomenadione, then recheck promptly and repeat if necessary according to the UK protocol and patient risk.
  • No bleeding with INR 5–8: omit one or two doses and investigate the cause; vitamin K is not routinely required unless individual bleeding risk is high.
  • PCC dosing is product and INR based: for Beriplex, 25, 35 or 50 IU factor IX/kg for INR 2–3.9, 4–6 or above 6 respectively, with stated maximum doses.
  • Bridge acute VTE with therapeutic heparin for at least 5 days and until the INR has been therapeutic for the protocol-defined period because early protein C depletion is not immediate protection.
  • Provide an anticoagulant record and consistent advice on missed doses, vitamin-K-containing food, alcohol, interacting medicines, pregnancy and when to seek urgent help.

Key red flags

New neurological deficit, severe headache, collapse or head injury while taking warfarin requires emergency intracranial imaging and reversal assessment irrespective of an apparently modest INR.

Haemodynamic instability, ongoing gastrointestinal bleeding, haemoptysis, haematuria with obstruction or a rapid haemoglobin fall requires major-haemorrhage escalation and source control.

An INR above 8, interacting antibiotic, acute liver or renal failure, inability to take nutrition or repeated dosing error predicts further INR rise even when bleeding is not yet visible.

Investigation priorities

01
First-line: urgent INR and FBCFirst stepFirst line

Quantify anticoagulant intensity and detect haemoglobin or platelet consequences.

Management branches

Major bleedingReverse immediately and control source

Bleeding is life-threatening, at a critical site, haemodynamically significant or uncontrolled.

  1. Stop warfarin, use ABCDE resuscitation, activate major-haemorrhage and obtain urgent INR, FBC, fibrinogen, renal, liver and group samples.
  2. Give four-factor PCC using the stocked product's INR and weight schedule plus 5–10 mg slow IV phytomenadione.
  3. Control the anatomical source, repeat INR and clinical assessment, then create a multidisciplinary anticoagulation restart plan.
Planned procedureMatch interruption to both risks

An invasive procedure is planned in a patient taking stable warfarin.

  1. Obtain procedure bleeding risk, indication, target INR, recent thrombosis and exact mechanical-valve details.
  2. Continue for supported low-risk procedures or stop at the locally specified interval and confirm pre-procedure INR; use bridging only when thrombotic risk justifies it.
  3. Restart when haemostasis permits, with a written timing and any bridging plan communicated across teams.

Key medicines

WarfarinUse a locally validated oral loading protocol and adjust the total weekly dose to the stated target INR; acute VTE additionally requires therapeutic heparin for at least 5 days and until INR is therapeutic for the locally defined interval.Check interacting medicines, liver function, nutrition, alcohol and adherence. Provide an anticoagulant record and close INR monitoring after change. It crosses the placenta and can cause embryopathy and fetal bleeding; pregnancy and conception require specialist planning.
PhytomenadioneFor major warfarin bleeding give 5–10 mg by slow intravenous injection with four-factor PCC; for INR above 8 without bleeding give 1–5 mg orally, then recheck and repeat only according to response and protocol.IV administration must be slow because severe anaphylactoid reactions have occurred. Oral treatment is slower and unsuitable as sole emergency therapy. Avoid unnecessarily large doses because prolonged warfarin resistance can complicate re-anticoagulation.
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Sources and review status5 sources · checked 27 Aug 2026 · clinical review pending+
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.

  • Specialist Pharmacy Service warfarin monitoringUK monitoring intervals, abnormal INR actions and safety review.
  • Beriplex Summary of Product CharacteristicsProduct-specific four-factor PCC reversal schedule and safety information.
  • Konakion MM phytomenadione Summary of Product CharacteristicsVitamin K administration and safety details.
  • Warfarin Summary of Product CharacteristicsLicensed dosing framework, contraindications, pregnancy and interactions.
  • NICE NG158 venous thromboembolic diseases recommendationsWarfarin bridging and VTE treatment pathway.

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

Authoring stateRapid draftClinical stateAwaiting reviewJurisdictionUnited Kingdom