Vitamin K antagonist (anticoagulant)
Warfarin sodium
Brand names: Coumadin, Marevan
Adult dose
Dose: Individualised; typical maintenance 1–9mg OD; load per local protocol
Route: Oral
Frequency: OD
Clinical pearls
- INR-guided dosing; target INR 2–3 (most indications) or 2.5–3.5 (mechanical heart valves)
- Bridging guidance per NICE NG185
- Reversal: vitamin K, PCC, FFP
Contraindications
- Active significant bleeding
- Pregnancy (especially 1st trimester and near term)
- Haemorrhagic stroke
- Severe hepatic impairment
- Hypersensitivity
Side effects
- Bleeding (major risk)
- Haematuria
- Skin necrosis (rare)
- Purple toe syndrome
- Hepatotoxicity (rare)
Interactions
- Extensive — antifungals, antibiotics, NSAIDs, antiplatelet agents, many CYP2C9 inhibitors/inducers, St John's wort, cranberry juice
- Consult BNF appendix
Monitoring
- INR (at least monthly when stable)
- Signs of bleeding
- Drug/food interactions at every review
Reference: BNF; NICE NG185; BSH; https://bnf.nice.org.uk/drugs/warfarin-sodium/. Verify against your local formulary and the latest BNF before prescribing.
Related
Curated clinical cross-links plus same-class fallbacks.
Calculators
- Warfarin Dose Adjustment Calculator · Anticoagulation
- HAS-BLED Score · Bleeding Risk
- CHADS₂ Score for AF Stroke Risk · Stroke Risk
- HEMORR₂HAGES Bleeding Risk Score · Prognosis
- ATRIA Bleeding Risk Score · Anticoagulation
- DOAC Score for Selecting Direct Oral Anticoagulant in Non-Valvular AF · Anticoagulation
Pathways
- Major Haemorrhage / Massive Transfusion · BCSH; RCOA; RCEM; RCS — BCSH Guidelines
- Anaemia Investigation · BSH / NICE
- Splenomegaly Workup · BSH; BMJ Best Practice
- Deep Vein Thrombosis Diagnosis and Treatment · NICE CG144 / NICE NG158
- Sickle Cell Crisis · BSH 2021 / BCSH
- Neutropenic Sepsis · NICE CG151 2012 / ESMO