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.
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.
Investigation priorities
Quantify anticoagulant intensity and detect haemoglobin or platelet consequences.
Management branches
Bleeding is life-threatening, at a critical site, haemodynamically significant or uncontrolled.
- Stop warfarin, use ABCDE resuscitation, activate major-haemorrhage and obtain urgent INR, FBC, fibrinogen, renal, liver and group samples.
- Give four-factor PCC using the stocked product's INR and weight schedule plus 5–10 mg slow IV phytomenadione.
An invasive procedure is planned in a patient taking stable warfarin.
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.
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.