Anticoagulants · Vitamin K antagonist
Warfarin
Dose
Start 5 mg OD (3 mg if elderly / liver disease); titrate to target INR
Mechanism
Inhibits VKORC1 → ↓ factors II, VII, IX, X and proteins C, S
Indications
- • Mechanical heart valve
- • Antiphospholipid syndrome
- • AF when DOAC contraindicated
Contraindications
- • Pregnancy (1st trimester, near delivery)
- • Active bleeding
Use
Many drug / food interactions; bridge with LMWH if rapid anticoagulation required.
Monitoring
INR — daily until stable then weekly → monthly. Target 2–3 (2.5–3.5 mechanical valve).
Side effects
- • Bleeding
- • Skin necrosis
- • Purple-toe syndrome
- • Teratogenic
Pregnancy safety
Avoid — use LMWH instead
Related in WardRound
Always confirm dose against your local formulary / BNF before prescribing.
