Warfarin
Start low and adjust to INR (usually 2–3). Many interactions. Reverse with vitamin K and prothrombin complex for major bleeding.
On this page
Dose
- Start 5 mg daily (lower, e.g. 2–3 mg, in the elderly, low weight, liver disease or interacting drugs), adjusted by INR.
- Overlap with enoxaparin for VTE until INR is in range for at least 2 days.
INR targets
| Indication | Target INR |
|---|---|
| AF, DVT/PE | 2.5 (range 2–3) |
| Mechanical mitral valve | 3.0–3.5 (per cardiology) |
| Rheumatic mitral stenosis with AF | 2–3 |
Reversal
| Situation | Action |
|---|---|
| INR 5–8, no bleeding | Hold 1–2 doses; consider oral vitamin K 1–2.5 mg if high bleeding risk |
| INR above 8, no bleeding | Hold; oral vitamin K 1–5 mg |
| Major bleeding | Stop; vitamin K 5–10 mg IV plus prothrombin complex concentrate (or FFP) |
Cautions
- Many interactions: antibiotics (clarithromycin, metronidazole, ciprofloxacin, co-trimoxazole), amiodarone, NSAIDs, antiepileptics, herbal medicines.
- Avoid in pregnancy (teratogenic), especially weeks 6–12.
Frequently asked questions
What is the target INR for AF?
2.0 to 3.0, aiming for 2.5.
Used in these guides
Sources
Doses on this page are typical doses from the sources above. Always confirm with a current drug reference, the product leaflet and your hospital protocol, especially in children, pregnancy and kidney or liver disease.
For FCPS Part 1
Revising for FCPS Part 1? Warfarin is covered in our textbook chapter Anticoagulants and antiplatelets, with practice MCQs.