Using warfarin for VTE (DVT/PE) - initiation, monitoring, duration and managing recurrence while anticoagulated
Overview
Warfarin (a vitamin K antagonist) is less commonly used first‑line than DOACs for many VTE patients, but correct initiation, overlap, monitoring, duration and response to recurrence remain core emergency‑medicine knowledge (NICE NG158). This section summarises practical, exam‑relevant actions and the NICE‑recommended process for suspected or confirmed recurrent VTE on warfarin.
Initiation and overlap with parenteral anticoagulation
- Start warfarin concurrently with a parenteral anticoagulant (therapeutic LMWH, fondaparinux or unfractionated heparin) when treating confirmed DVT or PE (NICE NG158).
- Continue the parenteral anticoagulant for at least 5 days and until the INR is ≥ 2.0 on two consecutive readings; only then stop the parenteral agent (NICE NG158).
- Initial warfarin dosing and early INR checks are determined by local anticoagulation service protocols.
- Monitor INR frequently during initiation (daily inpatient checks are typical until stable).
Therapeutic target and monitoring
- Therapeutic INR range for VTE treatment: 2.0-3.0 (commonly quoted midpoint 2.5). Follow local laboratory/anticoagulation targets where they differ (NICE NG158).
- Time in therapeutic range (TTR) matters: review recent INR history/TTR when assessing recurrence risk or treatment failure.
- In the ED: obtain an immediate INR, record recent INR results and dosing adherence before making management decisions.