Major bleeding: stop warfarin and give IV vitamin K plus four-factor prothrombin complex concentrate (not FFP if PCC is available). Manage a high INR by its level and whether there is bleeding.
Targets and indications
- AF and most VTE: INR 2.0 to 3.0
- Recurrent VTE on warfarin, or many mechanical valves: 2.5 to 3.5 (per cardiology)
- Document the indication, target range and intended duration
- A DOAC is now first-line for many of these (no valve, no severe renal impairment)
Interactions and counselling
- Many antibiotics (macrolides, metronidazole, ciprofloxacin), amiodarone and azoles raise the INR
- Enzyme inducers (rifampicin, carbamazepine) and vitamin K-rich diet changes lower it
- Advise consistent diet, caution with alcohol, and prompt INR checks after any new drug
- Give the patient a yellow anticoagulant book and alert card
Therapeutic INR
- Usually 2 to 3 (3.5 for mechanical valves)
- Continue, recheck per schedule
- Review interacting drugs
High INR, no bleeding
- 5 to 8: withhold 1 to 2 doses
- Over 8: withhold plus oral vitamin K
- Find the cause
Major bleeding
- Stop warfarin
- IV vitamin K plus prothrombin complex concentrate
- Resuscitate, senior help
Prescribing
1
1. Indication and target
Confirm and document the indication, target INR and duration.
Confirm and document the indication, target INR and duration.
↓
2
2. Loading and start
Use a local loading algorithm; cover with LMWH when immediate anticoagulation is needed (warfarin is initially prothrombotic).
Use a local loading algorithm; cover with LMWH when immediate anticoagulation is needed (warfarin is initially prothrombotic).
↓
3
3. Monitoring
Frequent INR until stable, then regular; recheck promptly after any interacting drug or illness.
Frequent INR until stable, then regular; recheck promptly after any interacting drug or illness.
↓
4
4. Procedures
Plan peri-operative interruption and bridging (if high thrombotic risk) per local policy.
Plan peri-operative interruption and bridging (if high thrombotic risk) per local policy.
High INR (no or minor bleeding)
- INR above 8, no or minor bleeding: stop warfarin, give oral vitamin K, recheck and restart when INR below 5
- INR 5 to 8, no bleeding: withhold 1 to 2 doses and reduce maintenance
- Minor bleeding with INR above 5: stop and give IV vitamin K
- Always find and address the cause of a high INR
Pitfalls
- Using FFP instead of PCC for major bleeding
- Starting warfarin without LMWH cover when immediate effect is needed
- Missing an interacting antibiotic
- Not rechecking INR after a drug or dietary change
MedPrep - www.medprep.uk - Educational revision aid only. Not clinical guidance. Doses are adult examples; check the BNF, current guidelines and local policy, and seek senior advice. Nov 2026